This should help
Match mounting involves positioning the tire onto the wheel to minimize or eliminate thefinal combination of radial force variation and/or imbalance (radial force variation is explained later in this article). One match mounting approach involves aligning the tire's point of maximum radial force variation (its high spot) to the wheel's radial low spot (where the wheel's radial runout is the lowest). This is called the Uniformity Method. The other approach involves simply aligning the tire's lightest balance point to the wheel's heaviest balance point, called the Weight Method.
OE tire suppliers are required to mark a tire's radial runout high point, and OE wheel makers are required to mark a wheel's radial runout low point. This makes it easy for the OEMs to match-mount tires to wheels from a radial force variation standpoint during production. In some cases, these marks are made with paint dots that help service technicians remount tires down the road. However, sometimes these marks are made using temporary stickers, which either fall off or are removed after mounting. This leaves no readily visible reference marks for the tire technician for future service.
If a tire does feature color dots on the sidewall, one or two dots may be used. A red dot indicates the tire's radial runout high point. A yellow dot indicates the tire's point of least weight, from a balance standpoint.
For decades, it was common practice in the aftermarket to mount a tire so its red dot aligned with the wheel's valve stem, since the valve stem area was normally assumed to be the wheel's lowest point of radial runout. Aligning the tires high point to the wheel's low point (theoretically) reduces or eliminates the chance of developing a radial force variation (RFV) in the tire/wheel assembly.' RFV (again, an issue of runout, not imbalance) can cause a vibration that might be mistakenly diagnosed as an imbalance problem.
Times change. With the advent of styled custom wheels, the valve stem location may no longer indicate the wheel's low radial runout spot. In other words, it may no longer be viable to assume that aligning a tire's.red dot to the wheel's valve stem will address any potential RFV issues.
Consequently, a procedure that was once easy has now become complicated. The only way to accurately matchmount a tire to a wheel is to actually measure tire and wheel runout. The end goal remains the same: to align the tire's high point to the wheel's low point. The wheel itself can be easily checked for radial runout by mounting it to a hub and slowly rotating it while monitoring the rim edge with a rigidly mounted dial gauge. However, the only acceptable method to check the assembled tire/wheel package for radial uniformity under load is to use a state-of-the-art wheel balancing machine that features a load-roller that applies road-simulated load to the inflated tire. Such a machine will not only check for dynamic balance but will also locate the tire's high spot. If this high spot doesn't correlate to the wheel's low spot, the machine will let you know where to relocate the tire on the wheel to minirnize RFV
If you don't have access to a roadwheel type of balancing machine, and you don't know where a wheel's lowest radial runout spot is located, you can default to using the Weight Method, which involves aligning the tire's yellow dot to the wheel's valve stem.
As you can see, tire/wheel match mounting isn't a cut-and-dried method. Your approach to match mounting will depend on several variables:
* whether the tire is runout- and weight-matched,
* whether the wheels low runout spot can be determined, and
* whether you have access to a loadapplying balancing machine.
Regardless of the specific approach you take, it's important to understand that "stacked-up" runout and imbalance conditions can be addressed. Of course, once tire matching has been accomplished, the mounted package must then be checked and corrected for dynamic balance.
There are two types of radial runout -static and dynamic. Static runout, as we noted earlier, refers to the high spot of the tire, a physical characteristic that can be measured with no load placed on the tire. Radial force variation, however, refers to a dynamic runout condition, which occurs only when the tire runs at speed, under load, due to variations in construction stiffness.
Some times "not knowing" is better!