EDITED DEC 3 RD 2017 Below is a modified communication to an article I wrote in Brake and Front End Magazine in 2015 that can be viewed at http://www.brakeandfrontend.com/on-car-wheel-balancing-wheel-to-hubindexing/ Wheel-to-Hub Match Balancing David Scribner, AUTHOR Off-car wheel balancers do an excellent job of measuring dynamic unbalance static and couple and many also measure tire/wheel assembly non-uniformity, radial runout or what we will simply define as RFV to help eliminate vibration and verify the assembly is balanced and round when rolling. Two assumptions are made with off-car balancers that can become problematic: 1. The technician incorrectly assumes he has centered the wheel on the balancer. If the wheel is not centered, all of the measurements and attempts to repair the unbalance are compromised when it changes as it is placed on the axle hub. 2. The technician assumes that the centerline of the wheel remains unchanged from the balancer when it is placed on the axle hub. The purpose of this article is to address assumption No. 2, which is not controlled and unmeasurable. The assembly centerline does not remain unchanged from the balancer to the vehicle hub on virtually all wheels with hub bores and lug nuts and studs securing the wheel to the vehicle. On-car balancing solves many issues that off-car balancing cannot address because the wheel assembly is not perfectly centered on the vehicle due to small clearances that can make a big difference in radial force variation ride quality due to
eccentricity changes and static and couple unbalance error created at the interface between the off-car balanced wheel and when is attached to the axle hub. Standard clearances between the wheel hub bore and the vehicle hub are often at least +0.2 mm (+0.008 ) in order for the wheel to slide onto the vehicle hub. When the wheel is installed, gravity imperceptibly pulls it downward to induce a radial runout change of at least +0.016. The wheel is now off-center enough to add or subtract from the runout of the assembly and also add to the residual static unbalance in the wheel depending on the angle of the remaining Runout Force Vector. This fact is supported by numerous NVH tire company service engineers, and Ford and Jaguar have TSBs with service guideline recommendations written in 2005-2007 which address on-car cancellation of residual tire/wheel RFV by taking advantage of the wheel hub-bore-to-vehicle-hub clearance. Virtually every vehicle that is measured for RFV can benefit from using a hub-boreto-vehicle-hub clearance indexing to assist in canceling the remaining RFV or static force in the assembly during installation. Wheel Balancers Alone Do Not Solve All Tire & Wheel Related Vibration. Todays s tire and wheels are better quality than they were 20 years ago. Rims are virtually all aluminum and machined round. Tires are better quality and more uniform. It remains important to measure out of round due to tire mounting variation as tires beads are now much tighter and often insufficient lubrication is used. There are also items that can cause flat spotting and out of round to a tire after it leaves the factory. Wheel Balancers that measure out of round allow the balanced assembly allow the technician to mark the high point of the assembly quickly after it is balanced. This is all that s needed in most cases to assure a superior ride quality. RFV wheel balancers should be used index the high point of the tire-wheel assembly and place it on the vehicle at TDC on the vehicle hub before tightening the lug nuts
to cancel remaining eccentricity. This best practice will improve ride quality results and in most cases eliminate time-consuming match mounting. With this method there is likely no longer a need (on a majority of applications) to match mount. As an example, an assembly that measured 0.30 RFV (~40 lbs. of Road Force ) when indexed at TDC would drop down before tightening the lug nuts, and end up with approximately a 0.020 RFV that is within vehicle tolerances to ensure a smooth ride. In the past if that assembly had been randomly mounted a 20 lb. Road Force assembly and the high point had ended up randomly at BDC, the 20 lb. assembly would have ended up a 35 lb. assembly which is out of specification according to General Motors TSB guidelines for vehicle sensitivity limits. Many hub bore clearances are higher than the nominal 0.2 mm (0.008 ). Indexing the high point/stiff spot of the assembly and placing it at TDC before torqueing the lug nuts is a best practice that should be provided by every tire shop that wants to solve vibration and not just balance tires. Any shop that balances and wants to improve their quality of work tire should upgrade their balancer to include RFV measurement capability to be sure their wheel assemblies are balanced and also round when rolling when placed on the vehicle. Marking the high point after balancing and placing it on the vehicle at TDC takes virtually no extra time; ensures a significantly better balance and guarantees a happier customer every time!
Simple, Time Saving, Better Balance TDC Index Process: 1. With the wheel properly centered on the balancer, measure RFV and balance the tire assembly 2. Before removing the assembly from the balancer, rotate the high point to 12 o clock (TDC) using the prompts on the balancer screen. 3. With a tire crayon, mark the high point/stiff spot on the inside of the rim edge and tire inner sidewall. 4. Place the assembly on the vehicle hub with the index mark at TDC. 5. Install and torque the lug nuts/lug bolts per factory specification.
When indexing the tire/wheel assembly on the balancer, be sure to mark the inside rim edge with the tire sidewall. This is done so if the customer returns with a vibration, possible slippage between the rim and tire can be determined. This can be due to excessive lubrication used when mounting or due to a hard stop or fit issues between the flange and tire. On UHP vehicles, customers should be cautioned to avoid spirited driving for at least 500 miles after tire mounting service has been performed.