In this issue: Sequoia power steering rack service Match-mounting wheels and tires Oxygen sensor circuit diagnosis
PHASE MATCHING Often referred to as match mounting, phase matching involves mounting the tire onto the wheel to align the tire s point of maximum dynamic runout (radial force variation, or RFV) with the wheel s point of minimum radial runout. Toyota tires and wheels are factory assembled to minimize MATCH-MOUNTING WHEELS/TIRES Chasing vibrational complaints the effects of RFV. All OEM wheel assemblies are phase matched to align the tire s point of maximum RFV to the wheel s point of minimum RFV. The tire s maximum RFV is generally indicated by a red dot on the tire sidewall. During mounting, this red dot should be aligned with the white dot on an OEM steel wheel (the white dot indicates the wheel s minimum radial runout point). On alloy wheels, the tire s red dot should be aligned with the valve stem, as the valve stem area is the Toyota wheel s point of minimum radial runout. Note that the tire may also feature a yellow dot, which indicates the tire s point of least weight. This dot may be referenced during balancing issues. Toyota emphasizes that even if dynamic wheel balance is correct, misalignment of the red dot may likely result in a vibration complaint. On Toyota OEM tires and wheels, always align the tire s red dot to the wheel s white dot (or valve stem, in the case of a Toyota alloy wheel). NOTE: If the vehicle has been fitted with aftermarket alloy wheels, it is possible that the valve stem location may not indicate the wheel s point of minimum radial runout. This is because some aftermarket alloy wheels may have been designed to locate the valve stem in a visually appealing location, instead of at the point of minimum runout. A red dot on the tire sidewall indicates the tire s point of maximum radial force variation. Always align a red dot on the tire with a white dot on the wheel, or with the wheel s valve position. RADIAL FORCE VARIATION (RFV) There are two types of radial runout runout deviation that can be measured statically and that which may only show itself 14 STAR Service News
under dynamic conditions when the tire runs with a load. Static runout, as we noted earlier, refers to a high spot on the tire, a physical characteristic that can be measured with no load placed on the tire. Radial force variation, however, refers to a runout condition that only occurs when the tire runs at speed, under load, due to variations in construction stiffness. When a tire s contact patch meets the road surface, its sidewall flexes, absorbing road forces, much like a spring. The rigidity of the tire s sidewall varies slightly along the tire s circumference. The variation in sidewall rigidity is caused by tire construction differences, material distribution and radial runout. All tires are manufactured with a degree of RFV, simply due to manufacturing tolerances, and in most cases, these slight variations don t cause a problem. However, excessive radial force variation will cause the axle s spindle to deflect upwards as the tire s stiffest area meets the road surface. This force results in a wheel tramp vibration. If excessive RFV is determined to be the problem (after verifying that the source of the vibration is not caused by wheel balance, tire, hub or axle runout, or suspension and steering component wear), the only solution is to replace the tire. Radial force variation is sonamed because the radius of the tire varies according to vehicle speed and load. Of course, any tire, because of its compliance, will slightly vary in radius at the load spot during operation. Although a radial force might be the result of a runout area that is pronounced enough to affect the tire s impact on the road, a radial force variation may occur if the tire has appreciably different soft spots and stiff spots in the carcass and/or tread or in the sidewall construction. Given the high quality control processes used by today s tire makers, it s rare that a force variation problem will occur, but when it does, it can be a tricky demon to chase. Even though no problems may be found as the tire rotates on the balancer, when the tire experiences a load, the transition of the harder and softer sections of the tire may create a series of harmonic vibrations as the tire contacts and leaves the road surface. Depending on conditions, this harmonic may occur once per revolution of the tire, or it may occur in a series of multiple vibrations per revolution. It s possible that this phenomenon may vary Valve stem according to changes in tire pressure, vehicle speed, individual tire load and the road surface conditions, all of which may serve to reduce and/or amplify the vibration problem. In other words, the vibration that the driver feels may not occur with any one rate of speed, or on any one road surface, because the problem may appear only under a specific combination of these variables. If a tire/wheel will not balance properly, or if a vibration exists after a successful balance job, don t automatically blame the tire. If you haven t checked the hub and wheel for runout, you may be jumping to conclusions. If, however, all balance, static runout and chassis parts variables have been exhausted, then it may be time to suspect a radial force variation problem. In order to check for and attempt to actually verify a dynamic radial runout condition, a spinbalancer with a built-in load roller is recommended. This type of balance machine places a load Valve stem The red dot on a tire sidewall (of an OEM tire) indicates the tire s position of maximum radial force variation. During tire mounting, this point can be aligned with the wheel s white dot (on steel wheels) or the valve stem location on alloy wheels. If a yellow dot is present on the tire, this indicates the tire s point of least weight. In order to minimize RFV, align the red dot to the wheel s white dot or to the valve stem. STAR Service News 15
(which attempts to simulate road load) onto the tire as it s spun, while monitoring and recording variances of runout. If load variation is found, this may be corrected to an acceptable state via balancing weights, or in extreme cases, it may verify that the tire should be replaced. THE DYNAMIC EFFECT OF RFV A minimum range of between.3 to.5 ounce (7-14 grams) of imbalance is usually enough for the average motorist to notice an imbalance-induced vibration. If a vehicle is sensitive enough to exhibit noticeable vibration at only.3 -.5 ounces of imbalance, that same amount of vibration may be present with as little as 10 to 15 pounds of radial force variation, which (although hard to believe) can be caused by as little as.010 inch -.015 inch of loaded radial runout. Using this as an example, it s easy to see how loaded runout Stiff spot The tire s flexible sidewall serves as the first, or initial, spring in the vehicle s suspension. Excessive variations in sidewall stiffness/flexibility can result in a vibration complaint as a result of dynamic radial runout, or radial force variation. A yellow dot on the tire indicates the tire s point of least weight. If no red dot is present, this yellow dot may be aligned with the wheel s white dot (if present) or with the wheel s valve stem, in order to minimize imbalance. can dramatically affect vibration. In other words, a little bit of loaded tire runout variance can result in a notable impact on operating smoothness or harshness. One method of phase matching is performed using a radar chart. The radar chart allows you to measure and plot the runout at 12 positions around the circumference of both the tire and the wheel. The method can be used to correct either lateral or radial runout. 1. Mount a dial indicator to measure either the radial or the lateral runout of the tire (whichever needs correction). 2. Divide the tire and wheel into 12 equal segments using tire chalk or masking tape. 3. Locate the wheel valve stem. The stem position will be considered as the 12 o clock position. Zero the dial indicator. 4. Place a mark under the 12 o clock position on the chart. This distance (from the outer edge of the chart) is the zero point. All other marks will be + (plus) or - (minus). 5. Rotate the tire clockwise to the 1 o clock position and note the indicated runout. 6. Plot this value under the 1 o clock position on the chart. Each box should represent 0.005 inch or 0.010 inch. If the indicated value is larger than zero, the mark should be above the zero line. If the indicated value is less than zero, the mark should be below the zero line. 7. Continue in this manner for the remaining 10 points around the tire circumference and connect the plotted points, forming the outer circle. 8. Perform the same steps for wheel runout, beginning again at the 12 o clock point. Plot the 16 STAR Service News
wheel values inside of the tire circle. 9. Connect each of the 12 plotted points between the tire and the wheel circles. 10. Measure the length of the connecting lines. The longest line indicates the point of maximum total runout and the shortest line indicates the point of minimum total runout. To reduce total runout, the tire must be dismounted from the wheel. Positioning the tire with the maximum tire runout, aligned with the point of minimum wheel runout should reduce the amount of total runout. After remounting, total runout at the tire must be re-measured to confirm that the runout has been reduced to within specification. If the runout is still excessive, and wheel runout itself is within specification, the tire should be replaced. Bear in mind that the above procedure, while allowing you This example shows a tire that features both red and yellow dots at the same location on the tire, which indicates that this tire s point of maximum RFV and its point of least weight share the same location. to minimize static radial runout, does not address dynamic radial force variation. The most efficient way to measure and to attempt to correct a radial force variation problem is to check the wheel/tire assembly on a balancing machine that is equipped with a road force feature. ORDERS OF VIBRATION A single vibrating force may generate more than one vibra- Tire Wheel The radar chart can be used to accomplish phase matching. Keep in mind that this addresses static runout, not dynamic radial force variation. STAR Service News 17
tion. For example, an out of balance tire can develop multiple vibrations due to the distortion of the tire as it rotates. The distortion of the tire is caused by centrifugal force as the tire rotates. As the tire rotates, the heavy spot on the tire causes an up-anddown motion as it contacts the road surface. This will induce a vibration into the suspension and steering system which will be felt by the driver. A vibration caused by a heavy spot is a first-order vibration. It occurs once per revolution of the tire. A first-order vibration can be the largest amplitude vibration caused by imbalance. Due to Radial runout Lateral runout Top view Radial runout appears as an eccentric or egg-shaped tire during operation, resulting in a vertical (up/down) movement as the wheel and tire assembly rotates. Lateral runout appears as horizontal movement (side-to-side) of the wheel/tire assembly, causing a shimmy condition. Imbalance First-order vibration once per revolution Imbalance Second-order vibration twice per revolution Tire distortion Imbalance Third-order vibration three times per revolution If an imbalance condition is present, the tire begins to change shape during rotation as a result of centrifugal force, causing the tire to distort and become out-of-round during operation. 18 STAR Service News
centrifugal force and the heavy spot, the tire changes shape, raising additional high spots on the tire. As these spots contact the road, they also cause an up/down motion that is induced into the suspension and steering systems. This second vibration is caused by a second bump in the tire as a result of the tire s change in shape. It is usually smaller in amplitude than the first-order vibration. This is called second-order vibration. Because there are two vibrations within one revolution of the tire, the second-order vibration will be approximately twice the frequency of the first order. The third vibration is caused by a third bump as a result of the tire s change in shape. It is generally smaller in amplitude than the second-order vibration. This vibration is called the third-order vibration. WHEEL PINPOINT DIAGNOSIS Body shake, steering flutter and steering shimmy complaints can be initially diagnosed by verifying bead seating, hub-to-wheel Inspect the assembly for proper bead seating. Improper bead seating can cause a radial runout condition of the tire. centering and wheel/tire runout. Check all four tires for brand, size and specifications. Be sure to check for proper inflation pressures. Inspect for damage, deformation and wear. Inspect the tires for Check for proper wheel-to-hub centering. A wheel that is mounted off-center (beyond specification) will cause a radial runout condition unusual wear patterns. Inspect the tire and wheel to confirm proper bead seating on both front and rear bead areas. Hub-to-wheel centering is important to ensure that the clearance is even and within the target value of 0.004 in. (0.1mm). If the clearance is beyond specification, the wheel can be rotated to minimize the difference. If the clearance is still out of specification, check the hub for runout to determine if the condition is caused by the wheel or the hub. Both radial and lateral runout can be checked. Radial runout is the change in the radius as the assembly rotates. This can be checked with a dial indicator that is mounted to a stationary position, parallel with the rotating plane. Slowly rotate the tire/ wheel assembly while mounted to the hub, through a complete 360 degree rotation. Lateral runout is the side-toside deviation of the rotating assembly. Position the dial indicator plunger at the wheel bead area and slowly rotate the assembly 360 degrees. The hub itself can be checked Vertical runout Lateral runout Radial runout (also called vertical runout) can cause a wheel tramping condition. Lateral runout can cause a shimmying condition. Radial runout Lateral runout When checking wheel radial runout, the dial indicator should be positioned vertically onto a horizontal area of the rim. For lateral runout, the indicator should contact the wheel s vertical surface, with the indicator placed at 90 degrees to the vertical wall of the rim. STAR Service News 19
The best method of determining a mounted tire s radial force variation is to run the assembly on a balancing machine that features a load-force road wheel. The example shown here is Hunter s GSP9700. for lateral runout using a dial indicator. The brake rotor can also be checked for lateral runout. With the rotor secured to the hub with at least three wheel nuts, a dial indicator can monitor the rotor surface as the rotor is slowly rotated 360 degrees. NOTE: When checking rotor runout, be sure to place the dial indicator plunger approximately 10mm or so from the rotor edge, to make sure that the indicator contacts the area of the rotor that is swept by the brake pads. While performing an inspection, the technician should be aware that a variety of steering and/or suspension components may contribute to vibration or shimmy complaints. Steering system component checks should include ball joint play, steering linkage play or damage, steering damper condition and condition of rubber bushings. Suspension system component checks should include suspension arms and bushings, springs, wheel bearing adjustment/condition and shock absorber condition. Bear in mind that while irregular tire wear may cause a vibration, any irregular tire wear is the result of another condition, such as incorrect wheel alignment or worn steering and/or suspension components. 20 STAR Service News