Tires and Wheels match mounting

Tires and wheels 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.

Radial force variation is so named because the radius of the tire varies according to vehicle speed and load. Of course, any tire, because of its pliability, will vary slightly in radius at the load spot during operation. Although a "radial force" might be the result of a runout area pronounced enough to affect the tires 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 precise quality control processes used by todays tire makers, it's rare that a force variation problem will occur. But when it does, it can be a tricky demon to chase.

CUSTOM WHEELS HANDLING

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 run out. 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 run out 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 match mount 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 run out 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 minimize RFV

If you don't have access to a road wheel type of balancing machine, and you don't know where a wheel's lowest radial run out 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.