Tire and Wheel Service

Transcription

1 CHAPTER 62 Tire and Wheel Service OBJECTIVES Upon completion of this chapter, you should be able to: Adjust tire pressures correctly for all cars. Rotate tires. Repair tire punctures in the correct manner. Determine causes of tire-related vibration. Understand and perform tire balancing. KEY TERMS lateral runout patch radial runout swaged tire plug tire rotation INTRODUCTION Tire service is a large area of automobile repair. The average owner can expect to replace at least one set of tires on his or her car. Tire life depends on tire quality, air pressure, vehicle weight, driving conditions, suspension condition, and wheel alignment. TIRE INFLATION Tire wear can be caused by incorrect inflation pressure (Figure 62.1). Tires can lose about 1 2 psi of pressure a month through permeation of the sidewall, and maybe more during hot weather. This is a normal occurrence. Think about a balloon you have found a few days after a birthday party. Like tires, balloons hold air they leak slowly. Maintaining correct air pressure is the most important factor in the safety, performance, and life expectancy of a tire. Underinflation is the most common cause of radial tire failures. Low tire pressure in a radial tire changes the normal defection of its sidewall. This raises the amount of heat generated within the tire s carcass. The following are results of low tire pressure: The temperature of the tire rises. The load-carrying capacity of the tire is lowered. Tire tread life is reduced. Fuel consumption increases. The outside edges of the tire wear excessively. A car will sometimes pull to the side that has a low tire, especially when it is a front tire. When an older car with bias tires had low air pressure, the driver would usually notice it in the handling of the vehicle because bias-type tires experience a strong pull to the side of a tire with lower inflation. However, a radial tire can often be run at a tire pressure that is below specifications without exhibiting handling symptoms. The following are results of high tire pressure: The center of the tread can wear excessively. A rough ride can result. The tire is actually the first part of the suspension and spring system. CHECKING AIR PRESSURE Vehicle owners should be encouraged to check tire air pressure at least once a month and prior to a long trip. The following items refer to the effect of temperature on tire pressure: As air within the tire expands with heat, pressure normally increases. Check air pressure when the tires are cold. It takes less than 3 minutes, or 1 mile of driving at moderate speeds, to make tires too hot to check accurately. According to Michelin Tires, this amount of driving can increase air pressure by 4 psi or more. Therefore, when adjusting pressure in a hot tire, add 4 psi to the maximum gauge reading desired. For instance, if the recommended cold pressure is 24 psi and the gauge reads 26 psi, fill the tire to 28 psi. Be sure to recheck the tire the next day when it is cold. 1145

2 1146 CHAPTER 62 Center tread wear Outside tread wear Overinflation Underinflation (a) Contact patch area (b) Contact patch area Figure 62.1 (a) Overinflation wears the center of the tread. (b) Underinflation results in excessive outer tread wear. NOTE: According to the Rubber Manufacturers Association (RMA), customers should be advised to check their tire pressures prior to driving while the tires are still cold. In the event they find a low tire, after a short drive to a service facility that has an air compressor, air can be added in the amount that the tire was underinflated. Air should not be let out of a tire when it is hot. Each change in outside temperature of 10 F will result in about 1 psi change in tire pressure. A hot tire with pressure that is lower than the recommended cold pressure is seriously underinflated. Cold tire pressure should never be higher than the maximum pressure molded into the tire sidewall. Tire inflation pressures should always be the same for both tires on one axle so ride and handling are not affected. An accurate air pressure gauge must be used to check tire pressures (Figure 62.2). A normally inflated Read pressure here Figure 62.2 A tire pressure gauge showing 34 psi.

3 Tire and Wheel Service 1147 radial tire has a bulging sidewall, and tire pressure must be dangerously low before there is a visible difference. Figure 62.3 compares two tires with a 10-pound difference in pressure. Older, bias-type tires had relatively stiff tire sidewalls, compared to modern radial tires. When they were low on pressure, there was a visible difference in the sidewall appearance. ADJUSTING TIRE PRESSURE All valve stems should be equipped with screw caps. They keep out dirt and moisture and provide a backup in case the valve core leaks. Before adding air to a tire, blow air through the air chuck to clear it so dirt is not forced into the valve core. A high-quality tire gauge should be used; inexpensive gauges are often inaccurate. One type of gauge is a part of the air chuck (Figure 62.4). When permanently installed on an air hose, these air gauges are often abused and become inaccurate. Tire pressure gauges are usually equipped with a pin that can be used to release air (Figure 62.5). Some tire air chucks and gauges have two sides that can be used to inflate and check tire pressures (Figure 62.6). The top side is handy to use when checking and inflating inner tires on trucks and motorhomes with dual wheels. Typical Tire Pressure Loss The U.S. government has mandated the installation of tire pressure monitoring systems (TPMS) on all new vehicles manufactured since This law was phased in before that time so many older vehicles are Gauge 30 psi Figure 62.4 This type of tire pressure gauge is rarely accurate. 20 psi Figure 62.3 The appearance of a radial tire sidewall changes very little with inflation pressure. Valve core To release air Figure 62.5 A pin on a typical tire pressure gauge used to deflate the tire after too much pressure is added.

4 1148 CHAPTER 62 This side is used for inner duals INFLATION PRESSURE Typical tire pressure loss due to leakage 20 June July Aug. Sep. Oct. Nov. Dec. MONTH Figure 62.6 Either side of this tool can be used for easier access to the valve stem. equipped with TPMS. Tire pressure monitoring came about because a significant number of vehicles on the road at any one time had one or more tires with dangerously low tire pressure. Consider these possible effects from not checking tire pressures regularly. If you fill your tires during the summer when the outside air temperature is 90 F and do not check them again for 6 months, the pressure will be considerably lower. A typical tire loses 1 psi in pressure each month. When combined with a 60 F temperature change in seasonal climates, the pressure change in the tire can be substantial. Figure 62.7 shows typical pressure changes under three conditions: loss from typical leakage, loss from temperature, and a combination of the two. TIRE WEAR According to the Goodyear Tire and Rubber Company, a 4 psi decrease in pressure below the recommended amount can result in a 10% loss of tread life. Additional losses of air pressure can result in even more wear and the possibility of serious damage to the tire. Underinflation can also cause the edges of the tire to wear (see Figure 14.2). Other than excessive wear resulting from an incorrect toe alignment setting, the fastest tire wear occurs during hard cornering, braking, and acceleration. Rough pavement can also contribute to accelerated tire wear. Slow-speed sharp cornering wears the front tires. High-speed cornering, on the other hand, will remove tread from the tires on the side of the vehicle where weight is transferred. When a tire wears to within 1 16" ( 2 32") of the bottom of its tread, wear bars begin to become more obvious INFLATION PRESSURE INFLATION PRESSURE TEMPERATURE Inflation loss from temperature only June July Aug. Sep. Oct. Nov. Dec. MONTH Total monthly and 22 temperature change 20 June July Aug. Sep. Oct. Nov. Dec. MONTH Figure 62.7 Changes in tire inflation due to time and variations in temperature. at regularly spaced areas around the tread circumference (see Figure 14.3). The wear bars are raised areas cast into the bottom of the tire tread area to indicate when the tread has become worn beyond its safe limit. The RMA recommends that tires with 1 16" of remaining tread depth be replaced. These tires are unsafe in wet weather and more apt to be damaged by road hazards. Federal regulations require vehicles in excess of 10,000 pounds gross vehicle weight (GVW) to have 4 32" minimum tread depth on front tires. The upper edge of

5 Tire and Wheel Service 1149 Wear bars Figure 62.8 Markers cast into the tire sidewall indicate the location of the wear bars in the base of the tread. the tire sidewall has triangles or manufacturer-specific markers that point to the locations of the wear bars (Figure 62.8). When a tire tread has scalloped or cupped wear, this is usually because the tire has been hopping up and down on the road. This movement, called wheel tramp (see Figure 62.61), results from bad shock absorbers, worn ball joints or control arm bushings, out-ofbalance tires, or too much tire and wheel runout. On some front-wheel-drive cars, the front tires develop abnormal tire wear. Some manufacturers specify tire rotation at very low mileage intervals to help compensate for this. Tire rotation is covered in more detail later in this chapter. Inspect the tire for physical damage. When a vehicle is driven on a tire that is flat or underinflated, damage to the tire can occur. Look for evidence of tread or sidewall separation. This might show up as an out-of-round tread or there may be visible deformities on the outside of the tire. However, sometimes damage from underinflation is not visible from the outside of the tire and can only be determined after the tire has been removed from the wheel. SIDEWALL CHECKS Sidewall cracks result from age and years of exposure to the sun and ozone (smog). Cracks on the exposed side of tire sidewalls are common with recreational vehicles (RVs). When an RV is parked in the same place for long periods and the tires have not been regularly rotated, the sidewalls on the side of the vehicle that have been exposed to daily sunlight will often be the only ones with cracks. Motorhome tires can be many years old before the tread wears out because RV driving tends to be seasonal and mostly on the highway, where wear is minimal. According to the RMA, a slight sidewall indentation (also known as sidewall undulation) is a normal characteristic of radial tire construction that does not affect the performance of the tire (Figure 62.9). The indentations are due to overlaps in the cord material of about 3 8". Although indentations are normal, if the tire bulges, there is no supporting cord and the tire must be replaced. If there is any question concerning the sidewall appearance, the tire should be removed from service and inspected by a tire dealer or manufacturer representative. Cuts or cracks in the sidewall that allow cords to be exposed are cause for replacement of the tire. RVs and light trucks with dual rear tires often experience uneven wear on the rear tires. Dual wheel tire diameter must be within ¼" of each other. TIRE ROTATION All vehicles experience the most wear on front tires. This is because they are used for steering and also because the weight of the vehicle transfers forward during a stop. Switching tires between positions on the vehicle is called tire rotation. Rotating tires on a regular basis will allow them to wear more evenly. Then they can be replaced four at a time. Most manufacturers specify regular rotation intervals. When there is no recommendation, rotation is recommended at 6,000 to 8,000 miles or before that if tire wear is evident. Figure 62.9 Slight indentations in the sidewall of a radial tire are normal. VINTAGE TIRES In the past, moving radial tires to the other side of the car was not recommended, but this is no longer true as long as there is not a specified rotation pattern to the tire. If one front tire shows uneven wear, it can be switched with the other front tire.

6 1150 CHAPTER 62 Front-wheel-drive cars experience far more wear on the front tires than the rear ones. A typical front-wheel drive rotation pattern calls for moving the front tires to the rear on the same side of the car. Then the rear tires are moved to the front, but to opposite corners of the vehicle. This is done to even out drive cornering scrub wear that occurs as the footprint of a radial tire squirms against the pavement (Figure 62.10). This results in a sawtooth heel-and-toe wear pattern on the tread (Figure 62.11) that is smoothed by rotating the tires to a different side of the vehicle. If sawtooth is allowed to develop, noise and vibration can result, along with accelerated tread wear. Figure shows typical generic rotation patterns for front-wheel drive (FWD) and rear-wheel-drive (RWD) vehicles. FWD vehicles use the same pattern as RWD vehicles. Cross the non-driving wheels to the drive wheels: with FWD, X-to-the-front and with RWD, X-to-the-rear. Front-wheel drive Rear-wheel drive Figure Typical tire rotation patterns. With frontwheel drive, X-to-the-front ; with rear-wheel drive, X-to-the-rear. SHOP TIP Remember: When rotating tires, Cross to the drive wheels. Footprint deforms here Figure Scrub wear that occurs as the footprint of a radial tire squirms against the pavement during cornering. Most cars are equipped with only an emergency compact spare, which is not rotated onto the vehicle. When a vehicle has a full-size spare tire, insert the spare into the rotation pattern at the right rear and reposition the tire that would normally have been installed on the right rear as the new spare. A few vehicles have front tires that are smaller than the rears. Do not rotate these tires to the rear. Some tires are designed to be mounted and run in only one direction. They are rotated from front to rear on the same side of the vehicle. To be cross-rotated, they are removed from the rim and remounted so they will still rotate in the designated direction. Exaggerated line Figure Sawtooth heel-and-toe wear pattern on radial tire tread. VINTAGE TIRES Paired tires should be of the same size designation, construction, and tread design. According to the RMA, if radial and non-radial tires are used on the same vehicle, put the radials on the rear. A new tire will sometimes cause the vehicle to pull to one side or the other because of tire conicity

7 Tire and Wheel Service 1151 SHOP TIP Remove lug nuts using the tightening pattern to avoid warping a hot rotor. Figure Tire conicity results in a pull. Do not loosen the lug nuts when the CAUTION wheel is on the ground. The car can fall down. Have someone hold the brakes applied while you loosen them with the wheel off the ground. VINTAGE TIRES Most lug nuts have right-hand threads that are loosened when turned counterclockwise. A few vehicles have left-hand threads on the lug nuts on one side of the car. These are labeled with an L on the end of the lug stud. or an off-center belt (Figure 62.13). These are problems resulting from errors made during manufacture. Building a tire requires much hand work. After a tire rotation, a vehicle will sometimes pull to one side or the other as well. This can happen if the offending tire was previously installed on the rear of the car. When the defective tire is moved from its position at a non-steering rear wheel, it can suddenly cause a problem when installed at the front, where it can affect steering. A defective tire with off-center belts can also result in outside shoulder wear on the tire. REMOVING AND TIGHTENING LUG NUTS Loosening and removing lug nuts is easiest when done with an impact wrench. When the wheel is in the air, it will not have to be held from turning. Just as with other fasteners, lug bolts are stretched when they are properly installed so that they maintain clamping force. Lug nuts that are loose allow the wheel to exert all of the weight of the vehicle on the lug bolts, rather than on the wheel. Lug nut torque specifications are available for all vehicles. Tighten evenly in a crisscross pattern. Use a torque wrench to avoid warping a disc brake rotor (Figure 62.14). Use a socket extension between the socket and the torque wrench as needed so your hand and the handle of the torque wrench will be able to clear the tire sidewall (Figure 62.15). Use a ½" drive extension only. Inaccurate torque readings can result from the use of excessively long or smaller 3 8" drive extensions. Lug nuts on steel wheels are tapered on the side that faces the wheel. Some aluminum wheels have Four-lug wheel Five-lug wheel Six-lug wheel Figure Torque sequences for various wheel lug configurations.

8 1152 CHAPTER 62 Locking lug nut Key Clearance 1 Extension 4 Torque wrench Figure Use a socket extension to provide clearance to the tire sidewall. Tapered end faces to wheel. Figure Lug nuts for steel wheels are tapered on the side that faces the wheel. tapered lug nuts as well. There are also lug nuts that are closed on one end and can only be installed in one direction (Figure 62.16). CASE HISTORY A customer complained of a clunking sound and poor vehicle handling. He asked a service advisor to inspect the vehicle. She was amazed to find all of the lug nuts on inside out. All of the holes in the rims were damaged so badly that new wheels were required. Antitheft lug nuts, popular with custom wheels, require a special key (Figure 62.17). This is a good thing, but what do you do if the customer loses the key or forgets to leave it at your shop when the vehicle is left for a tire or brake repair? Most shops that do tire and brake repair own a special tool kit 3 2 Open end Covered end Figure A wheel lock nut and key. to remove locking lug nuts when there is no key. It has several adapters that are wedged against the outside of the locking lug nut. The inside of each adapter is tapered (Figure 62.18a). A hammer is used to force the adapter onto the outside of the wheel lock (Figure 62.18b). To loosen the wheel lock, an impact wrench is used to hammer against the removal tool while it is held firmly against the wheel lock (Figure 62.18c). A special type of lug nut is used with aluminum wheels. It is usually equipped with an integral washer. The shank on the nut must not be too long or it can bottom out, causing a loose wheel (Figure 62.19). The lug nut must also be of a smaller diameter than the hole in the wheel to provide enough clearance to turn when tightening. SHOP TIP Apply antiseize lubricant to the outside of aluminum wheel lug nuts before installation. This will prevent electrolysis between the steel lug nuts and the aluminum wheel. REPAIRING WHEEL STUDS Sometimes a lug bolt will be stripped or broken. When only one or two of the first threads are damaged, they can be cleaned up with a thread chaser. A broken lug bolt can be replaced. VINTAGE WHEEL STUDS Some older drums and disc brakes rotors are fastened tight to the hub. The studs are swaged, which means that they are deformed to keep them tight (see Vintage Figure 58.2),. The swaged area can be cut off with a special tool to make them easier to remove. Drum brakes are no longer found on the fronts of newer vehicles.

9 Tire and Wheel Service 1153 Washer Tapered areas Wheel lock Correct length (a) Too long (b) (a) Figure Lug nuts in cast aluminum wheels: (a) is correct, and (b) would allow the wheel to be loose. Tool Wheel hub Wheel lug nut (b) Washers Figure Installing a new lug stud. (c) Figure (a) The inside of the adapter is tapered. (b) A hammer is used to force the adapter over the lug nut. (c) The lug nut is removed using an impact wrench. When the rotor or drum separates easily from the hub, the lugs can usually be driven from the hub with a brass hammer or punch. If additional effort is needed, a tie-rod press can be used to force the lug bolt out of its hole. A new lug stud is installed using an inverted lug nut and washers as shown in Figure REMOVING AND MOUNTING TIRES ON RIMS Before attempting to remove and install tires on wheel rims, there are some important things to know. Tires can explode and fingers can be cut off if proper caution is not observed. Be sure the tire is of the specified size and construction for the rating of the wheel. Check that the rim diameter matches the diameter molded on the tire sidewall. Tire problems such as leaks and vibrations can sometimes be traced to improperly mounted tires.

10 1154 CHAPTER 62 Deflate the Tire Before removing the tire from the wheel, remove the valve core to deflate the tire completely. Figure shows a tool used to remove the valve core. If the tire is to be patched and reinstalled without rebalancing, be sure to mark the locations of the valve stem and any wheel weights with a marking crayon. If another tire is to be installed on the rim, remove any balance weights from the rim first (Figure 62.22). Tire Changers Earlier tire changers had a center post; the tire was lifted onto it from the top. This had a tendency to cause back injuries. The rim clamp changer was originally developed in Europe (Figure 62.23). It is has become the predominant tire changer in North America as well. It does not rub against the wheel rim and it is easier to lift tires on and off. Tire changing requirements for high-performance and specialty aftermarket wheels and tires have presented new challenges. A new tire changer design has emerged in response to these needs (Figure 62.24). It Figure A rim clamp tire changer. Fits on valve core Figure A tool for removing and replacing valve cores. Tool Wheel weight Figure Remove wheel weights from the rim. Figure A new tire changer design that can be used with low-profile, specialty, and performance tires and wheels.

11 Tire and Wheel Service 1155 is capable of mounting and dismounting low-profile tires on larger diameter wheel rims. The procedures for mounting and dismounting all types of tires are similar. Unseating the Beads Before a tire can be removed from a wheel, both of its beads must be unseated from the bead seats (Figure 62.25). This is called breaking the beads. First, lubricate the beads with rubber lube to reduce friction between the tire and wheel. This prevents damage to the tire and makes it easier to remove from the rim. NOTE: Many late-model vehicles have a tire pressure monitor in each valve stem (Figure 62.26). Be certain that it is rotated so it is on the opposite side of the wheel from the bead breaker before breaking the bead. More information on TPMS service is found later in the chapter. Do not attempt to unseat the beads of an inflated tire. NOTE Do not strike the tire or rim with a hammer. Something is wrong if you need a hammer. When removing a tire from a rim, never let go of the tire iron. It can flip up and hit you. SAFETY Removing a Tire from the Wheel The upper tire bead can be pulled over the edge of the rim only after the bead on the bottom side of the tire is forced into the wheel s drop center (Figure 62.27). A bar called a tire iron is used to remove the tire from the wheel (Figure 62.28). First, the upper bead is pulled over the outside of the rim, followed by the lower one. Do not try to remove both beads at the same time. NOTE: Be careful! If you tear the bead, the tire will be ruined. If the bead does not come off the rim without binding: Be sure enough rubber lube has been applied to the bead. Double-check to see that the lower bead is totally into the drop center of the wheel. Drop center Figure Breaking the bead using a tire changer. Figure Both beads are in the drop center of the wheel while the bead is pulled over the edge of the tire. Wheel rotation Rubber lube on bead Tire pressure monitor Bead is in drop center of wheel Tire iron Figure Before dismounting a tire from a wheel, be sure that the tire pressure monitor is moved to the opposite side of the wheel from the bead breaker. Figure A tire iron is used to pull the top bead over the edge of the rim. Be sure that the other side of the tire bead is in the drop center of the wheel.

12 1156 CHAPTER 62 INSPECTING THE TIRE AND WHEEL After the tire is removed from the rim, inspect its inside for cuts, carcass damage, penetrating objects, loose cords, dirt, and liquid. Inspect the condition of each bead by pulling out on it in several places around its circumference. If there is a sharp bend in the bead, do not mount the tire. The bead wire could be broken. It is not worth taking a chance with someone s safety. SAFETY Never mount a tire or wheel that is damaged. This could result in injury or NOTE death to the occupant(s) of the vehicle; in such a case, the shop may be held liable in court for negligence, and the technician can face criminal charges. (a) Inspect the condition of the wheel rim for sharp edges, dents, cracks, and other damage. Small dents in the rim flange can be straightened. When there is a larger dent in the wheel, it must be checked for radial and lateral runout before it can be used. Excessive runout can cause the car to shake at highway speeds. Many newer tire machines have an attachment for measuring runout. Checking runout can also be done with a dial indicator. Spinning the wheel while holding a screwdriver near it for reference will give a good preliminary indication of whether a wheel is bent. Rust can damage the bead seat on a wheel. If the rust is on the surface only, it can be removed with a wire brush. If the bead seat is not smooth, the tire will have a slow leak and the wheel will need to be replaced. (b) Figure (a) Cut the bottom of the old valve stem. (b) The new valve stem is installed with a special tool. VALVE STEM SERVICE TPMS valve stems are made of EPDM artificial rubber or aluminum and are not typically replaced unless damaged. Ordinary rubber valve stems are customarily replaced when new tires are installed. The valve stem can also be replaced without removing the tire from the rim. This is done when an old valve stem becomes old and cracked or starts to leak. Leaks can be found by prying the stem to side and observing any air leakage. To remove a valve stem, cut it off with a knife (Figure 62.29a), or force it through the hole in the rim using the valve stem installing tool. Remember to install the valve stem before installing the tire on the wheel rim. To install the new stem, thread it into the installation tool, lubricate it with rubber lube, and pull it into the hole (Figure 62.29b). Be sure it is pulled all of the way into place and is properly seated in the hole in the rim. SHOP TIP A new valve stem comes with a new valve core. Remove the valve core before attempting to inflate the tire. TPMS Tire Mounting and Dismounting Be careful not to damage a direct-type TPMS when dismounting and mounting tires on rims. Do not force the tire over the sensor or it can be broken or the tire bead can be damaged. If the sensor is part of the valve stem (see Figure 62.26), be sure that the bead breaker is positioned across the wheel from the valve stem. If the wheel has a banded sensor, it will be mounted in the drop center, 180 degrees from the valve stem. Position the bead breaker accordingly. Cars with run-flat tires have used direct tire pressure monitors for many years. These tires have extra-stiff sidewalls and can be especially difficult to work with.

13 Tire and Wheel Service 1157 RUBBER LUBRICANT Radial tire sidewalls are flexible and their tire beads are designed with a close tolerance for a tight fit to the rim. During inflation, the beads are not easily forced into position. If the beads are not seated properly, the tire can have an out-of-round condition when inflated that will make it difficult to balance. Lubricate both tire beads with an appropriate rubber lube (Figure 62.30). Good-quality rubber lube is slippery and fast drying. Lubricate the bead seats on the rim with rubber lube also. Using rubber lube provides the following advantages: Rubber lube reduces friction between the tire beads and the edge of the rim during mounting. Rubber lube helps to seal around the bead during initial inflation of the tire. Friction between the bead seats and the tire bead will be reduced when inflating the tire. This is important so that the beads will be all of the way seated and the tire tread will not be distorted. Remember: Safety glasses should always be worn when inflating a tire. The following are some cautions to observe regarding rubber lubricants: Do not use petroleum products, which will damage the rubber in the tire. Rubber lube should not be diluted with water, which can rust a steel wheel rim. Do not use silicone lubricants or liquid soaps, which will allow the tire to spin on the rim. Directional Tires Some tires are designed to be run in only one direction. These will have an arrow indicating the direction of Figure Some tires are directional and must be kept on the same side of the vehicle during tire rotation. Figure A tire s serial number is usually found on the inside of the tire. rotation (Figure 62.31). Check the tire sidewall to see if there are direction arrows. Be certain that the correct side of the tire is facing out. Some tires have whitewalls or special lettering. All tires have a serial number, which is on the back side of the tire (Figure 62.32). Figure Lubricate both tire beads with an appropriate rubber lubricant. INSTALL THE TIRE Clamp the wheel to the tire changer with the narrow bead ledge up. Install the inside bead of the tire over the flange of the rim (Figure 62.33). As more and more of the bead is passed over the edge of the rim flange, force the bead down into the drop center of the wheel. This is important! If one side of the bead is not in the drop center, the diagonal mounting distance will be excessive and the other side will not be

14 1158 CHAPTER 62 Push here Narrow bead ledge Wheel rotation Wide bead ledge Figure The narrow bead ledge is up and the lower tire bead is in the drop center of the wheel. Bead is in drop center Figure As the bead is drawn over the edge of the wheel rim, it is important that the other side of the bead stays in the drop center. able to be stretched over the flange (Figure 62.34). Be careful not to damage a tire pressure monitor during bead installation. When the first bead is totally installed and positioned in the drop center of the wheel, install the other bead over the flange of the rim (Figure 62.35). Some tires have a colored dot on their sidewall to indicate the high or low side of force variation. Unfortunately, lining the valve stem up with the mark presents inconsistent results because some manufacturers use the mark to label the high point, whereas others use it to label the low point. Force variation measurement is covered later in this chapter. Inflating the Tire Most tire machines include a provision for safely inflating the tire. SAFETY Inflation can be the most dangerous part of tire installation, because tires can NOTE explode during inflation. If a machine is not equipped with a lock-down clamp to hold the wheel, inflate the tire in a safety cage. An extension hose is used with a clip-on air valve so the technician can stand away from the tire during inflation. Do not leave tools on the tire sidewall when inflating the tire. Seating the Beads Tubeless tires require a substantial volume of airflow for the beads to start to seat on the rim. It is sometimes difficult to get a tire to begin airing up. Narrow bead ledge Diagonal mounting distance Wide bead ledge Drop center Figure The bead must be all the way past the edge of the narrow bead ledge or the diagonal mounting distance will not be sufficient to allow the bead to pass over the edge of the wheel.

15 Tire and Wheel Service 1159 SHOP TIP If the valve core is removed from the valve stem when filling the tire, a greater volume of air can enter the tire. This is helpful in seating the beads. Most tire changers have a large inflation reservoir attached to a metal sealing ring (Figure 62.36). The sealing ring forces a high volume of air through jets into the area surrounding the lower bead (Figure 62.37). The air reservoir is required so that there will be a tremendous amount of airflow at once. If air was simply pumped through the normal shop air lines, the volume of air could not be maintained. Air jets Figure Air from these jets helps seat the lower bead during initial tire inflation. Apply rubber lubricant to both upper and lower beads CASE HISTORY A technician was attempting to use a recently purchased glass bead blaster. The pressure gauge showed 120 psi. When the pedal was first applied, the glass beads and air from the blast nozzle cleaned effectively for only about 1 second. Then the pressure would drop to about 60 psi. Further investigation showed that the machine had been fitted with a small regulator with 3 8" pipe nipples on its inlet and outlet sides. The supply line from the air compressor, however, was a ¾" pipe. The smaller regulator was acting as a restriction or orifice in the line. Installing a larger ¾" regulator solved the problem. This is an application of Pascal s law. When air is moving, the pressure reading after an orifice will be lower than the pressure on its front side. When trying to fill a tire with air from a remote air compressor, the air line acts like a similar orifice. This is why an inflation chamber is used. High pressure through tire valve required to ensure sufficient flow on difficult tires Lift tire up to assist seal on top side Air inflation jets Usually the last to pop is the top bead 40 psi max. Visually confirm bead seating WARNING Do not stand over tire during inflation Figure Hold the tire against the top bead seat and use the air jets to seal the bottom bead.

16 1160 CHAPTER 62 If the tire is pulled against the upper bead seat while inflating it, both beads will usually seat. It is more difficult to seat the beads on wide rims. When you cannot inflate the tire because the tire beads are not seating against the bead seats: You can try to use the bead breaking shovel to force the outer bead against the inner bead in an attempt to push it down over the safety hump. Another trick is to bounce the tire onto the floor so air trapped inside can force the beads outward. The top bead is usually the last bead to move into position on its bead seat. As each bead finally slips over the rim s safety hump on the inside of the bead seat, you can expect to hear a loud pop; this is normal. Most tire changers have an in-line dial indicator type tire gauge. Do not apply more than 40 psi (or the maximum pressure listed on the tire sidewall) when attempting to seat the beads. If 40 psi is not enough to completely seat the beads, break them back down again. Then thoroughly lubricate the tire and rim before attempting to seat the beads again. Be sure to reposition the tire on the rim as needed before filling it with air. SAFETY When inflating a conventional tire to a pressure higher than 40 psi, be NOTE sure it is in a safety cage. Be careful to have the valve stem pointing away, in case it shoots out of the wheel. Inflating a tire while it is clamped from the outside is dangerous. Run-flat tires often require higher pressures to seat the beads. When a tire is inflated in a safety cage, it can be inflated to a maximum of about 50 psi (3.5 bar) to seat the beads. For especially difficult tire inflations, such as with wider wheels, some tire specialty shops have a collection of rubber bead seating bladders. A different size bladder is needed for each rim diameter. Tire Changer Precautions Rim clamp tire changers are sometimes referred to as table top steel jaw tire changers. There are some potential problems to be aware of when using these machines. Custom rims can be damaged on the inside by steel jaw clamp teeth. This can be a problem because many wheel designs allow much of the inside of the rim to be visible. Also, the anticorrosion coating that was applied during manufacture can be damaged. Custom wheels should be clamped from the outside. If the wheel does not remain tight on the clamping table it can spin, resulting in scuffing to the outside of Figure The sidewall can be damaged if the bead breaker is positioned too far away from the edge of the wheel rim as shown here. the inner rim edge. This can happen during a difficult installation or when there is a problem with the tire changer. Other tire changer concerns include: If shop air pressure drops due to high air demand, the clamps can slip. With repeated use, jaws wear out and will no longer grip tightly. As parts of the apply assembly wear, clamping force can become uneven and the jaws on the clamping table will not all apply with the same force. Low-profile tires sometimes have sections of sidewall that extend beyond the flange of the rim to protect the rim from damage when it rubs against a curb (see Figure 61.21a). When using a shovel-type bead breaker, this is in an area where the shovel would normally be applied. If the shovel slips toward the wheel rim, it can scratch or chip the wheel. If the shovel is applied to the sidewall closer to the tread area, it can damage the tire sidewall (Figure 62.38). Some types of tire changers are designed to prevent this. MOUNTING HIGH-PERFORMANCE TIRES A vehicle can have many thousands of dollars invested in its tires and wheels. Aftermarket wheels can cost between $100 and $1,500 each, and speed-rated tires can cost up to $600 or more each. An incorrectly serviced tire can end up costing a business over $1,000. If not done correctly, removing and replacing a highperformance tire with a tighter tire bead can result in a tear to the bead or damage to the tire sidewall. NOTE: Tire service should not be performed without proper equipment. Tires with aspect ratios less than 60 will typically call for more sophisticated tire equipment.

17 Tire and Wheel Service 1161 Tires that require more than 40 psi to CAUTION inflate must always be installed in an inflation cage. When reinflating low-profile tires, psi could be required to seat the beads, so these tires must be installed in a safety cage during inflation. Low-profile tires are also more apt to suffer bead damage during removal from the rim. Always apply rubber lubricant to both beads during removal and installation of tires. BEAD ROLLER TIRE CHANGER High-performance, low-profile tires are removed and replaced using a tire changer that breaks the bead loose with rollers, instead of the typical shovel-type bead breaker used on conventional tire changers. It was developed for use with high-performance wheels and tires. It uses hydraulic bead rollers on the top and bottom to loosen the beads with a force of up to 4,000 lb (Figure 62.39). The tulip clamping system uses pads protected by rubber, which allows the wheel to shift without damaging its internal surface. The wheel is centered to its hub mount by a spring-loaded device. Almost any size wheel, from 5" to 23" in diameter and up to 19" wide, can be mounted in this changer. If the tire is incorrectly mounted and binding occurs, the mounting head will break. But this saves expensive tires and wheels from damage. Mounting heads for this tire changer are easy to replace and are inexpensive. Tire removal is similar to the rim clamp changer, except that the bead is automatically pushed into the drop center while the bead lever tool pulls the bead over the edge of the rim. Special tool blocks are used to assist in removing and installing extremely low-profile tires (Figure 62.40). Install the Valve Core Install the valve core. It can be torqued to 3 to 6 inchpounds using a special valve core installation tool for TPMS valve stems. The valve core should not extend above the top of the valve stem. If it does, the valve cap could contact the top of the valve core and let air out. A shorter valve core should be installed. After the valve core is installed, inflate the tire to the amount recommended on the vehicle placard. Then install the valve stem cap. (a) TIRE RUNOUT When a tire is not mounted correctly or the wheel is out-of-round, it will have runout. This means the tire is not round as it spins. Vibration and handling problems result if the tire is higher on one side than the other. (b) Figure Hydraulic bead rollers break the bead seat on the top (a) and bottom (b). Figure The tire is held in position using blocks.

18 1162 CHAPTER 62 Pirelli Tire recommends that tires be inflated initially to 40 psi in order to thoroughly seat the beads. Sometimes a tire is not seated evenly on the rim following inflation. The sidewall has centering ribs or locating rings (Figure 62.41). Inspect them to see that they are even with the edge of the rim flange all the way around the tire. If not, the beads will need to be broken down again and relubricated before reinflation to center the tire. Improvement is sometimes made by dismounting and remounting the tire on the rim 180 degrees from its original position. Sometimes there is excessive runout when a second-quality or blemished tire has been installed. Runout can be either lateral (sidewall wobble) or radial (up-and-down tread movement) (Figure 62.42). Runout can be checked with a dial indicator. TIRE REPAIR Tires are sometimes repaired, if they are still in good condition and damage to the tire has not occurred. Whether or not to repair a tire is both an economical and a practical decision. Checking for Leaks A tank full of water is used to check for leaks. Roll the inflated tire slowly around in the tank while looking for bubbles at the area where the tread meets the water (Figure 62.43). This an effective way to locate the very Water Figure Check for bubbles at the water line as you spin the tire slowly in the tank. Steel wheel rim Rusty bead seat Radial runout Lateral runout Tire locating ring Figure Following inflation, check the locating ring to see that the tire is evenly mounted. Figure Tire runout can be either radial or lateral. Figure A slow leak was caused by this rusty bead seat on a steel wheel. small bubbles from a slow leak. If there are no bubbles at the tread line, hold the valve stem under water as you push it from side to side. Check carefully where the tire bead meets the rim as well. On a steel wheel, a rusty wheel rim can cause a leak here (Figure 62.44). Before removing a nail or screw, mark its location (Figure 62.45). As you remove it, pay attention to its angle of entry. During the repair, the hole will be reamed at the same angle as the injury to the tire. Inspecting the Tire Before you can inspect damage to a tire, it needs to be removed from the wheel. Businesses that do tire repair use a bead spreader to hold the beads apart during the tire inspection and repair. The tire must be dry prior to inspection. The entire outside and inside of the tire are carefully checked using a bright light to see that

19 Tire and Wheel Service 1163 Figure Mark the location of the injury and remove the nail or screw. it is not damaged from having been run flat. Check the outside of the tire for anything that could allow moisture to enter. Look for weather checking, cracks, or tread separation. Tires that should not be repaired include those that: Smell of burned rubber or have bluish discolored rubber on the sidewall flex area Have evidence of loose cords Have an inner liner that has blisters, bubbles, cracks, or the casing cord pattern showing through Are worn beyond the wear bars REPAIRING A TIRE Puncture repairs are done using a rubber tire plug and a patch. A tire can be repaired when the puncture is between the shoulder of the tread area, called the crown (Figure 62.46) if the diameter of the puncture is less than ¼". According to RMA guidelines, the repair area is between the edges of the outermost tread rows and a patch or plug is not to be used except in combination with the other. Very few businesses perform repairs to tire sidewalls, and repairs to the bead area can never be safely done. NOTE: Off-road and farm tires are often very expensive. Repairs to holes in the sidewall area or holes larger than ¼" in the tread area can sometimes be made but only by a special full-service tire facility. These are not traditional retail tire outlets. The RMA publishes industry-approved guidelines for the repair of all types of tires. Tire repairs are sometimes done incorrectly. For instance, rubber plugs are sometimes installed when the tire has not been removed from the tire. This is a substandard repair because the tire should be removed from the wheel and carefully inspected to verify that it is in good condition internally. A serious accident can result from a repair to a tire that has been run flat, has a hole that is too large to be repaired, or has suffered damage from an impact or a nail. Figure shows two (a) Crown Sidewall Beads Sidewall Figure Repairs are usually made only to the crown area. (b) Figure (a) A rim bruise break is caused by impact against something like a curb or pothole. (b) This damage was caused by driving for a short distance on a severely underinflated tire. Rubber Manufacturers Association

20 1164 CHAPTER 62 Figure This puncture is outside the crown area. It should not be repaired. examples of tire damage that cannot be seen without removing the tire from the wheel. How can you help a customer decide whether or not a tire can, or should, be repaired? Opinions differ. When the cost of a safe repair is considered against the cost of a new tire, the correct decision is often to replace the tire with a new one. When a puncture appears to be in an acceptable area of the tread, here is a good way to tell if a tire can be repaired. When reaming the puncture during the first stage of the repair, if you cannot feel the resistance of the steel belts, a passenger car tire should be replaced. The puncture shown in Figure turned out to be outside of the tread area supported by the belts. Although the tire tread was relatively unworn, it was replaced with a new one. Each tire manufacturer publishes repairability standards to distribute to their dealers. Some manufacturers say that high-speed tires are not repairable, because these tires are used on powerful cars at high rates of speed. Others say that a high-speed tire will lose its speed rating if repaired. Repair procedures are sometimes supplied for high-speed tires. In any event, be certain that the repair procedure is industry sanctioned and that the tire is removed from the wheel before attempting a repair. An industry-sanctioned tire repair includes: Removing the tire from the wheel Inspecting the tire carefully Running a reamer or drill through the hole Installing a tire plug Smoothing the inside of the plug Installing a patch on the inside of the tire Figure Use rubber cleaning solvent and a scraper to clean the tire liner. of a patch unless the surface is properly prepared. Use rubber-cleaning solvent to clean the area where the new patch will be installed. Then use a scraper to clean the liner because this is a more effective method of removing oils, grease, or silicone (Figure 62.49). Plugging the Hole A radial tire with a puncture through a steel belt most likely has steel exposed to the elements. Moisture can cause damage to exposed areas of the belt. Therefore, it is advisable that the puncture be filled with a rubber plug, followed by further repair with a patch. Ream the Hole When an intruding force is of sufficient strength to penetrate the steel belts beneath the tire tread, sharp pieces of torn steel from the belt are likely to remain. These sharp edges will cut away at the new plug until it begins to leak if they are not smoothed off. Before the plug is installed into the hole, it must be reamed (Figure 62.50). PREPARING A TIRE FOR REPAIR Before repairing a tire puncture, the inside of the tire liner must be cleaned. The rough inner surface of a tire is covered with a material that will prevent the adhesion Figure Ream the hole to remove metal burrs from the belts.

21 Tire and Wheel Service 1165 Before reaming the puncture hole, probe it with an awl to determine the direction of the puncture. Then ream the hole from the same direction as the original injury. The motor that drives the drill or reamer should be turned at less than 5,000 rpm to avoid excess heat. Following reaming, vulcanizing cement is applied to a rubber plug before it is inserted into the hole until about ½" of the plug extends above the tread surface (Figure 62.51). Cut the plug flush with the tread surface on the outside of the tire but be careful not to stretch the plug while cutting it (Figure 62.52). Use a flexible knife to cut off the inside of the plug 1 8" to 1 16" above the inner liner. Then use a fine buffing stone and a low-speed buffer motor (less than 5,000 rpm) to buff the plug lightly until it is just above the surface of the inner liner (Figure 62.53). First, outline an area ½" around the outside of the patch with a marking crayon. Figure Buff the area where the patch will be installed. Tire plug Insertion tool Apply vulcanizing cement Figure Apply vulcanizing cement to the plug and install it in the hole. NOTE: Be careful not to buff through the liner into the casing plies. Just clean the surface of the rubber. If a portion of steel belt extends into the inside of the tire, grind it carefully away. Compressed air contains oil and moisture so it should not be used to remove dust from the interior of the tire. It must be vacuumed away. PATCHING THE TIRE After a plug has been cut flush with the inside of the tire liner, clean and scrape the area with rubber cleaning solvent and a scraper. When the cleaned area has dried, apply an even amount of vulcanizing cement to the buffed area where the patch is to be installed (Figure 62.54). When vulcanizing cement is in acceptable condition, it is liquid. If it has solidified or is like jelly, it should be discarded. Figure Cut the plug off flush with the tread surface. Figure Apply vulcanizing cement to the buffed area where the patch is to be installed.

22 1166 CHAPTER 62 Before applying the patch, allow the vulcanizing cement to completely dry. Drying time varies with temperature and humidity. SHOP TIP Moving the puncture to a higher position will allow the cement to dry quicker and more evenly because solvents are heavier than air. Install the Patch Carefully remove the covering from the adhesive side of the patch. Be careful not to touch the sticky adhesive. Center the patch over the hole, making sure that the bead arrows on the patch point to the beads of the tire. Then carefully apply it to the inner liner. Next, roll the patch into place, using a corrugated tire stitcher (Figure 62.55). Roll firmly from the center outward, using as much hand pressure as possible. After stitching is complete, remove the thin plastic covering from the top of the patch. Combination Plug/Patches Sometimes a plug is combined with a patch (Figure 62.56a). These can only be used when the hole goes straight into the tire. If the hole is slanted, use a plug with a separate patch. Some combination plug/patches are mushroom shaped and must be installed using a special plug installation tool (Figure 62.56b). Be sure to dip a blunt probe in vulcanizing cement and push it through the hole to thoroughly coat the walls of the hole. After reinstalling the tire on the wheel and inflating it, use water to double-check for bubbles to confirm that the leak has been fixed. Liquid Puncture Sealants. Liquid puncture sealants are sold in automotive stores. Although these products may be handy when a flat tire occurs, they will plug (a) (b) Figure (a) A combination plug/patch. (b) One type of combination plug/patch installed with an insertion tool. the sensing port on TPMS sensors, can cause imbalance problems, and are not recommended by tire manufacturers. SAFETY Some puncture sealants are flammable and can result in an explosion from a NOTE spark caused during an external plug repair. The spark results when drilling through the steel belts of the tire. Removing the tire from the wheel lessens the danger of an explosion. Figure Use the stitcher to seat the patch to the tire casing. TIRE AND WHEEL BALANCE Tire imbalance is one of several possible causes of vehicle vibration. Other possibilities include a bent axle or wheel rim, an out-of-phase driveshaft, a bad universal joint, or misaligned drivetrain components. Tire imbalance can result in cupped tire wear, traction loss, and premature wear to steering and suspension parts. Although tire imbalance is not always the cause of vehicle vibration, it is a major cause. Front tires are the most prone to exhibit symptoms from imbalance. Vibration from rear tire imbalance may not be as obvious, but tire wear can still result.

23 Tire and Wheel Service 1167 Imbalance results when the weight of a tire s materials is not equally distributed around the tire and one side of the tire is heavier than the other. This can be due to errors in manufacturing, or it can result from tire wear. A new tire will sometimes have a minor imbalance that is correctable by adding a small amount of weight to the wheel rim at specified points. When the addition of an excessive amount of weight is necessary to achieve balance, a defective tire could be the cause. It is also possible that the tire might be incorrectly seated on the wheel rim. NOTE: Out-of-round wheels and tires can be balanced but will still cause vibration from wheel tramp. Runout of less than 0.030" will not usually result in noticeable vibration. Runout of more than 0.125" calls for replacement of the tire or wheel. Although it is theoretically possible to balance a box, it will still be square. Wheel Weights To correct imbalance, wheel weights are attached to the rim (Figure 62.57). Clip-on wheel weights are attached to the rim using a wheel weight hammer (see Figure 62.22). Several styles of clip-on weights are available in increments of ¼ ounce. Different types of Weight clamp clips are available. Some have an extra long clip for fitting under wheel covers. Another style has a wider, larger clip to fit on pickup truck wheels. NOTE: Aluminum wheels that have a flange that will accept a clip-on weight require alloy or coated clips so they will not corrode the wheel. Tape weights are also available for aluminum wheels. These are lead strips that are cut to length (Figure 62.58). They are attached to the wheel with double-sided tape after cleaning a place on the inside of the wheel with sandpaper. Sometimes they are installed on the inside and outside of the wheel, but this is unsightly. Chrome weight strips are available also. NOTE: Be careful when working around aluminum wheels. They are easily scratched. Plastic shields are available that cover tire tools to prevent damage. Lead Wheel Weight Ban Lead wheel weights have been used on cars and trucks since the 1930s. The European Commission banned lead wheel weights in 2005 and they are now banned in several states in the United States as well. Alternative wheel weights are made of steel or zinc or a zinc alloy called ZAMA, which combines zinc, aluminum, and copper. Lead-free tape weights are also available. The level of lead in the environment has been estimated to be a thousand times greater than it was before the industrial age. Lead was banned for use in wheel weights because a substantial number of wheel weights fall off vehicles when they hit curbs or potholes or when making sharp turns. The lost weights are worn down by traffic and are thought to contribute to an increase in lead that enters storm drains, where it can have an adverse affect on water quality. A long list of health problems has been linked to lead exposure, with children being particularly affected. Light truck Aluminum wheel Adhesive backing Steel wheel Flush-mounted wheel covers Figure Wheel weights are installed on the wheel to counterbalance a tire. There are several styles for different applications. e a ght Tape a weight Figure Tape weights. Tape a weight

24 1168 CHAPTER 62 TYPES OF WHEEL BALANCE The two types of wheel-balancing are static and dynamic. Static means an object is stationary; static imbalance is measured with the wheel at rest. If a wheel with static imbalance were mounted on a spindle with the heavy spot at the top, the heavy spot would rotate to the lowest possible position on its own. If the wheel was in balance statically, it would not have a tendency to rotate by itself. Static imbalance subjects the wheel to vertical impacts that become worse with higher speed. These impacts occur when a tire has a heavy spot on one end of its tread (Figure 62.59). A small amount of imbalance when the wheel is at rest can amount to a great deal of pounding force when the wheel is spinning at highway speeds (Figure 62.60). For instance, if a 15" wheel is 1 ounce out of balance at rest, at 60 mph the pounding force will be 4.6 pounds. Static imbalance causes wear to mechanical parts. It also causes vibration and gouged tire tread wear, called cupping (see Figure 14.4). In severe cases, especially when accompanied by a bad shock absorber, a tire can hop so badly that it leaves the road surface. This is called wheel tramp (Figure 62.61). Imbalance During rotation imbalance force is outward away from rotation axis Rotation axis Figure When the heavy spot is rotated, force is directed out away from the center of the wheel. John Bean Company Tire hop Imbalance Figure Wheel tramp happens when speed and force to the imbalance become large enough to cause the tire to leave the road surface. The part of the tire in contact with the road is actually traveling at 0 mph. This is called static friction or static contact. During wheel tramp when the tire returns to the road, a small amount of its rubber is scrubbed off. This is because the tire was traveling at the same speed as the vehicle when it left the road surface. This scrubbing happens all around the tire, accounting for the cupped wear all around the entire circumference of the tread surface. Older, narrower bias tires were static-balanced. Static means an object is stationary. Although today s modern wheel balancers are capable of measuring the static imbalance of a spinning wheel, the name remains from when imbalance was measured with the wheel at rest on a bubble balancer. Static balancing, also called single-plane balancing, is done in a single plane where compensating weight is added on the opposite side of the wheel (Figure 62.62). If it were possible to put the compensating weight at exactly the same place on the opposite side of the tire, the amount of the weight would be exactly the same as the imbalance. Unfortunately, tires are sometimes heavier on one side of the tread than the other. Modern wheel balancers correct this imbalance. Static balancing is an option when using a computer wheel balancer. Although there are better ways of balancing aluminum wheels, this option might be used when John Bean Company Pounding force 3 oz. Imbalance Speed 2 oz. Imbalance Figure Pounding force increases as speed and the amount of imbalance increase. John Bean Company Imbalance Counter balance weight Figure To balance a tire in a single plane, compensating weight is added on the opposite side of the wheel. John Bean Company

25 Tire and Wheel Service 1169 Tape weight Axis of rotation Angle of imbalance compared to axis of wheel centerline Figure Location of weights for static balance. unsightly weights are not wanted on the outside of the wheel, When static-balancing an aluminum wheel, tape weights are fixed to the inside of the wheel at the center plane (Figure 62.63). COUPLE IMBALANCE When a tire is lopsided, with more of its weight on the outside or the inside of its tread, this is known as couple imbalance. Couple imbalance is only evident when the wheel is spinning. The wheel will have a tendency to shimmy, which also results in faster tire wear. A spinning heavy spot will seek the centerline of the tire (Figure 62.64). This is why the tire shim mies, Figure As the speed of the rotation increases, the imbalance moves toward the axis of rotation. or wobbles, from side to side. When the heavy spot is in the front, it pushes the wheel to one side. After the tire rotates one-half revolution, the heavy spot causes the wheel to try to turn in the opposite direction (Figure 62.65). This example shows what happens when there is an imbalance on only one side of the tire. However, there are usually imbalances on both sides of the tire, requiring counterbalancing weights to be installed on both sides of the wheel. When the imbalance is at the front, it steers the wheel left Direction of force at 180-degree intervals When the imbalance is at the rear, the wheel steers right John Bean Company Figure Action of dynamic or couple imbalance.

26 1170 CHAPTER 62 Control panel Safety hood Balance weight Balance weight Figure The amount of weight is split in half and put on both sides of the rim to avoid creating a couple imbalance. A wheel may be in static balance but not couple balance. If a tire has been statically balanced by adding all of the weight to one side of the offset wheel rim, that weight will be thrown side to side in a different direction as the tire spins, resulting in shimmy. The correct way to balance a wheel statically is to split the amount of weight in half, with an equal amount of weight installed on both sides of the wheel (Fig ure 62.66). Pirelli Tire recommends this procedure anytime the amount of weight to be added exceeds 20 grams (0.71 oz.). DYNAMIC BALANCE Dynamic imbalance is the combination of both static and couple imbalance. It is unlikely for a tire and wheel to have static imbalance and not have couple imbalance as well. Dynamic balance means balance in motion. It is also called two-plane balance because it measures side-to-side (lateral) force as well as up-anddown (axial/radial) force. Lateral forces are felt when a steering wheel moves back and forth. A dynamic wheel balancer spins the wheel and locates sources of vibration. The computer splits the tire into two halves and measures lateral and axial/ radial forces on each side of the tire s center. Weight is added to the proper side of the rim to correct the imbalance. A tire that is dynamically balanced will also be statically balanced. Dynamic balancing can be done with a computer balancer or with an on-the-car spin balancer. COMPUTER BALANCERS Computer wheel balancers (Figure 62.67) are very popular and easy to use for balancing tires in both the static and dynamic planes. Computer balancing is usually performed after a new tire has been installed on a wheel. The wheel is mounted on either a horizontal or Rim width calipers Centering cone Centering cone spring Figure A computer wheel balancer. a vertical threaded shaft using adapters that are supplied with the machine. Most balancers have a horizontal shaft because it is easier to lift the tire onto the balancer. When lifting a heavy truck tire, a special hydraulic tire jack is used. CENTERING THE WHEEL ON THE BALANCER One cause of imbalance is when a wheel was not installed correctly on the wheel balancer. According to the FMC Corporation, a 36-pound tire and wheel assembly that is off-center by only 0.006" will result in a ½-ounce imbalance error. The best method of centering a wheel on the wheel balancer is the method specified by the manufacturer. There are two ways that wheels are centered (see Chapter 61): Hub-centric this is when the hole at the center of the wheel locates the wheel on the wheel hub or axle (Figure 62.68). Lug-centric this is when the lug nuts center the wheel. SHOP TIP Weight storage tray To determine whether or not a wheel is hub-centric, see if the wheel fits the hub snugly with the lug nuts removed. If you can move the wheel up and down or side to side, the wheel is lug-centric. Preparation for Mounting the Wheel The backing plate and wheel lug flange must be clean and undamaged. Be sure that the wheel and tire have Hennessy Industries, Inc.

27 Tire and Wheel Service 1171 Centering feature Figure The center hole of a hub-centric wheel fits on the hub. This is a rear wheel and hub. accuracy in centering. This is because they expand when tightened, eliminating all clearance between the collet and the shaft. Mounting Lug-Centric Wheels To mount lug-centric wheels, use a special lugcentering adapter (Figure 62.70). The arms on the adapter are attached in different places, depending on the number of lug holes in the wheel. There are only five adapter arms. With six lug wheels, use three arms. With eight lug wheels, use four arms. After the arms are installed and tightened on the adapter, the adapter is held against the mounting flange on the wheel balancer while screws are installed and tightened (Figure 62.71). Special lug nuts hold the wheel against the adapter (Figure 62.72). Do not overtighten them. any rocks or foreign objects removed from them before attempting to balance a tire. When the wheel and tire assembly spins, look for signs of obvious runout. Double-check the mounting if the tire wobbles visibly. Mounting Hub-Centric Wheels Use a centering cone to mount a hub-centric stampedsteel wheel. The most accurate centering system is to install it from the back side of the wheel. This is because the center hole was originally stamped from the back. Figure shows the recommended mounting arrangement on the wheel balancer. It is important that the centering cone fit the shaft snugly. When new, it has about 0.001" clearance. Expandable collets are available that provide the most Figure A lug-centric adapter installed on a wheel balancer. It can be configured with three, four, or five adjustable arms. Faceplate Spring Cone Retaining drum Hub nut Figure Recommended computer balancer mounting arrangement for hub-centric wheels.

28 1172 CHAPTER 62 Program the Wheel Balancer After the wheel is mounted, three references are programmed into the balancer: The width of the rim, measured by a rim caliper (Figure 62.73) The location of the flange on the wheel, measured by a gauge (Figure 62.74) The diameter of the wheel (for instance: 13", 14", 15") After checking the tire pressure, the safety hood is lowered over the wheel to start the balancer. The wheel is spun for a short time and then stops. The balancer screen provides a readout telling how much weight to use and where it should be installed. After the weights have been put in place, the wheel is spun again to check for the accuracy of the balance Figure The lug-centric adapter is held against the balancer mounting flange while retaining screws are installed and tightened. Adapter lug nuts Rim width indication Take measurement from this area Figure Use a special caliper to measure the width of the rim. Apply its ends to the places on the inside and outside of the rim where wheel weights would be applied. Figure Special lug nuts hold the wheel against the lug-centric adapter. Measure to wheel weight location CASE HISTORY A man purchased a used Suburban that had aftermarket aluminum wheels and oversized tires. The tires appeared to be in good condition, with less than half of the tread worn. Unfortunately, they had been balanced incorrectly using adapters in the center hole instead of a lug-centric adapter. The tires had worn unevenly, developing cupped tread wear. They were now too far out of balance and had to be replaced. Distance number indication Figure This measurement tells the computer where the wheel is located on the balancer shaft.

29 Tire and Wheel Service 1173 and measured for imbalance. The heavy spot on the tire can be installed on the opposite of the heavy spot on the wheel to minimize the amount of weight that needs to be added. Figure Tape weights added to the inside of the wheel for cosmetic purposes. job. A reading of zero (or OK) on both sides of the wheel means that the wheel can be installed on the car. With tape weights, weights are often added in two places on the inside of the wheel (Figure 62.75). This is for cosmetic purposes. The balancer can be programmed so it knows where the innermost weight will be positioned. It makes its calculations for the amount of weight and position accordingly. SHOP TIP When balancing aluminum wheels with tape weights, use duct tape to temporarily attach the weights to the wheel during the initial balance. Install one weight on the wheel as near to the outside as possible. The other weights are installed on the inside edge of the wheel. NOTE: Be certain that there is enough clearance between the wheel weights and the disc brake caliper. MATCH MOUNTING Some computer balancers have an extra feature that matches the imbalance of a tire to the imbalance of a wheel. This procedure is used when a weight of more than 2 ounces is required on one side of a wheel. The tire is given an initial spin on the balancer to learn the location of the imbalance. Then it is deflated and broken down using a tire machine. The tire is rotated 180 degrees on the wheel. Then it is reinflated and rebalanced. The computer can now tell how much the wheel is out of balance and how much the tire is out of balance. If both the tire and wheel are within acceptable limits, the tire is once again rotated 180 degrees on the rim to complete the match mount. A wheel that is suspected of being out of balance can be installed on the tire balancer without a tire John Bean Company FORCE VARIATION Today s lighter vehicle designs are more sensitive to road feel. When a load is placed against a tire, there is a change in the stiffness of the sidewall and the tire s footprint. There can be stiffer or weaker areas of the tire when under load (Figure 62.76). Manufacturers have specifications and acceptable limits for this change, which is called force variation. A wheel and tire might be free of runout when measured with a dial indicator. Yet the tire might vibrate under load due to excessive force variation. Some tires come with a mark or a paint dot on their sidewall to indicate the high or low side of force variation. Unfortunately, this marking is not uniform among manufacturers; some manufacturers use the mark to label the high point, whereas others use it to label the low point. Also, it used to be that lining the valve stem up with the mark was all you needed to do. This is no longer applicable. On many of today s decorative wheels, the valve stem can be placed in various locations for cosmetic reasons. Lining up the mark with the valve stem could possibly result in an exaggeration of the problem. Measuring Force Variation Some tire balancers can measure force variation (Figure 62.77). The balancer identifies and locates tire and wheel problems caused by force variation, runout in the wheel (Figure 62.78), and the random position between the force variation and runout when the tire is mounted on the wheel. The balancer detects variations in wheel runout, and the computer recommends Figure There can be stiffer or weaker areas of the tire when under load. Hunter Engineering Company

30 1174 CHAPTER 62 Stiff spot on tire Matched Figure A tire balancer with a force roller. The force roller presses against the treads as the wheel spins. Low spot on wheel Figure Matching the high or stiff spot on the tire with the low spot on the wheel reduces vibration. Sensing roller Figure This wheel balancer detects wheel runout. a change in the tire and wheel positions to match the stiff or high spot on the tire with the low spot on the rim (Figure 62.79). This minimizes problems caused by force variation. INSTALLING THE WHEEL Before installing a wheel on a vehicle, double-check to see that the bolt holes in the wheel center are in good condition. You will occasionally find a steel wheel with worn bolt holes from a wheel that was loose, lug nuts that were installed upside down, or lug nuts that were overtightened. During wheel installation, finger-tighten the lug nuts to be sure they are not accidentally crossthreaded. Shake the wheel to align it with the centering area on the hub. Then cross-tighten the lug nuts to the correct specification using a torque wrench. Figure Torque sticks allow an impact wrench to tighten lug nuts to a specified torque setting within ±3% of their rated torque. Torque Sticks Some high-volume tire and brake shops use a tool called a torque stick, or torque socket (Figure 62.80) to initially tighten wheel lugs using an impact wrench. A torque stick is a special socket extension that fits between the impact wrench and the wheel lug socket. When the correct torque has been achieved, the shaft flexes in synchronization with the impact blows, preventing further torque increase beyond its rating. A torque stick used with a 400 ft.-lb impact wrench is said to be accurate to within 3% of its rated torque. Torque sticks come in different torque ratings. They are color coded and engraved with their footpound and Newton-meter rating.

31 Tire and Wheel Service 1175 Shop air pressure can change with CAUTION demands on the air compressor. This will change the tightening force of the torque stick. Before the vehicle leaves the shop, the final torque is always verified, using a torque wrench. TIRE PRESSURE MONITORING SYSTEM SERVICE When tires have been rotated or if a defective sensor is replaced, some TPMS require the computer to be reprogrammed with the unique sensor identification (ID) and its wheel position on the vehicle, front left, for instance. Many vehicles require a special electronic device for this. There are also some TPMS that are able to relearn without the aid of special tools. Some systems relearn simply by driving the car. Others relearn if the tire pressure is dropped very quickly. There were some systems before 2004 that used a magnet placed around the valve stem to trigger the TPMS sensor. Many shops use the electronic device to test the TPMS before working on a vehicle. When a tire has been broken down, a shop assumes liability; the vehicle cannot leave if the TPMS light is on. If the customer was informed beforehand that there is a TPMS problem, an estimate can be written and approved for the cost of the repair before beginning work on the vehicle. TPMS Tools Different types of TPMS measuring and resetting tools are available. Some are considerably more expensive than others, but higher volume shops consider them to be worth the extra cost. The sensor needs a means of displaying data. This can be onscreen or through a connection with a personal computer (PC). The device should be able to identify the correct TPMS and sensor and not become confused with signals from other TPMS sensors, key fobs, for instance. The technician needs to know whether the sensor has failed or if it has not been relearned by the system. Test results should show if the sensor s pressure port is blocked, whether temperature is too high, or if the battery is failing. A basic resetting tool, called a tire inflation positioning switch (TIPS), is an inexpensive alternative. It only does resetting and does not show tire pressure or temperature, sensor ID information, or condition of the battery. It is updatable through an Internet connection, using an interface module, USB cable, and PC. A mid-range, more advanced TPMS tool has no display but can show data when connected to a PC Figure A tire pressure monitor resetting and diagnosis tool with an integral display screen. and can print a report showing vehicle data. In addition to its resetting capability, it can show the sensor manufacturer and ID. It can also read the condition of the sensor battery as well as tire pressure and temperature. The most advanced TPMS tools have a display screen (Figure 62.81). They are menu-driven, listing all of the necessary steps for the technician to follow. Some of them also display testing information that would otherwise need to be located in a separate book. Some tools have more features than others. One manufacturer s tool might display pressure but not temperature or sensor battery condition, for instance. Rechargeable batteries are a good idea because the tool can discharge regular cells quickly. A service guide for TPMS will include service requirements, procedures for resetting monitors, all torque specifications, and instructions for dismounting and remounting tires (Figure 62.82). TPMS Service The TPMS sensor is replaced if it fails mechanically or electrically. It can have a problem with a low battery or a blocked pressure port. A common reason for replacement is when the sensor is damaged during tire removal from a wheel. Tire sealant can block the pressure inlet to the sensor. If there is evidence of tire sealant, the sensor should be replaced. There are special procedures to follow when replacing or reprogramming a tire pressure sensor. Automotive manufacturers typically use TPMS sensors made by at least two different vendors. Be sure you are replacing a sensor with one from the same vendor. When servicing a TPMS sensor, replace the grommet, nut, valve cap, and valve core. Do not use a brass valve core or unplated brass valve cap with an aluminum sensor stem. This can cause galvanic corrosion, resulting in a leaking tire. If the TPMS valve stem The TECH400 PLUS, by Bartec

32 1176 CHAPTER 62 Figure A service guide for tire pressure monitoring systems. is aluminum, a special nickel-plated valve core that resists electrolysis must be used. The torque range for the sensor retaining nut is 30 to 90 inch-pounds. There are special tools available for this, or you can use an inch-pound torque wrench. Mitchell Repair Information Co. The Mitchell1 name is used herein by permission from Mitchell International which has no ownership interests in Mitchell1. Figure The valve core is torqued using a special tool. The valve core must also be torqued correctly; torque range is only 3 to 5 inch-pounds. Special tools are available for this (Figure 62.83). If the wheel has a banded sensor, the TPMS tool is held on the tire, 180 degrees from the valve stem before activating it. If the TPMS is integral with the valve stem, the tool is held on the tire next to the valve stem before activation. Some systems automatically reprogram. Acura service information, for instance, says that the system relearns when the vehicle is driven for 40 seconds at a speed above 15 mph. When replacing a tire pressure sensor on these vehicles, be sure the vehicle is at least 10 feet from any pressure sensor not installed on the vehicle. Aftermarket Tire Pressure Monitor Systems Tire pressure monitors can be installed on vehicles that did not have them as original equipment (OE). They work in the same way as OE systems. Some of the direct systems have sensors that are integral with the valve stem and others are banded. The tires need to be dismounted to install the sensors. A module/display is mounted inside the vehicle to complete the job. REVIEW QUESTIONS 1. What kind of tire has a bulging sidewall when properly inflated, radial or bias? 2. What is the approximate amount of tire pressure increase as a tire warms up during driving? 3. At what tread depth do wear bars show up around the tire tread? 4. What is the name for the up-and-down action of a tire that causes scalloped tread wear? 5. What is applied to the tire bead before installing a tire on a rim? 6. Should the valve core be in or out of the valve stem when filling a tire on a tire changer with air to seat its beads? 7. A hole in the tire tread area is repaired using a patch and a. 8. A hole in the tire tread area of a steel-belted tire must be or before a plug can be installed. 9. What is the name of the tool used to clean the inside of a tire liner before installing a patch? 10. What type of wheel balance is measured with the wheel stationary? 11. If a 15" wheel is 1 ounce out of balance, when the wheel rotates at 60 mph, the pounding force will be pounds. 12. How fast is the part of the tire in contact with the road traveling?