What Is Match Mounting?

dding performance vehicle owners to your cus- tomer list can give a huge boost to your shop’s bot- tom line. These owners may be demanding—even picky—but they’ll pay well to get the jobA done exactly the way they want it. Some of the most common types of work done on performance vehicles in- volve the wheels and/or tires. The wheels are one of the most visible parts of a vehicle, so any work done on them must be top-notch—meaning clean, pretty and accurate. Custom wheel service can be broken down into two primary topics, essential- ly—tire match mounting and custom wheel handling. Since you’ll never mount a wheel without a tire, we’ll cov- er the ins and outs of tire match mounting first. What Is Match Mounting? Match mounting involves positioning the tire onto the wheel to minimize or eliminate the final 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 techni- cian 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 Mavrigian Mike Photos: 38 April 2008 runout high point. A yellow dot indicates the tire’s point of least weight, from a balance standpoint. For decades, it was common practice TIRETIRE MATCHMATCH in the aftermarket to mount a tire so its red dot aligned with the wheel’s valve stem, since the valve stem area was nor- mally assumed to be the wheel’s lowest point of radial runout. Aligning the tire’s high point to the wheel’s low point (the- oretically) reduces or eliminates the MOUNTINGMOUNTING 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 && CUSTOMCUSTOM styled custom wheels, the valve stem lo- cation may no longer indicate the wheel’s low radial runout spot. In other words, it may no longer be viable to as- sume that aligning a tire’s red dot to the wheel’s valve stem will address any po- tential RFV issues. WHEELWHEEL 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 HANDLING high point to the wheel’s low point. The HANDLING wheel itself can be easily checked for ra- BBYY MMIKEIKE MMAVRIGIANAVRIGIAN dial runout by mounting it to a hub and slowly rotating it while monitoring the Some of the most common types rim edge with a rigidly mounted dial Some of the most common types gauge. However, the only acceptable ofof workwork donedone onon performanceperformance method to check the assembled tire/wheel package for radial uniformity vehiclesvehicles involveinvolve thethe wheelswheels andand under load is to use a state-of-the-art wheel balancing machine that features a tires.tires. ThisThis overviewoverview ofof tiretire andand load-roller that applies road-simulated load to the inflated tire. Such a machine wheel-handlingwheel-handling proceduresprocedures will not only check for dynamic balance provides information but will also locate the tire’s high spot. If provides information this high spot doesn’t correlate to the you’llyou’ll needneed toto keepkeep wheel’s low spot, the machine will let you know where to relocate the tire on youryour customerscustomers the wheel to minimize RFV. If you don’t have access to a road- rollingrolling smoothsmooth wheel type of balancing machine, and you don’t know where a wheel’s lowest andand straight.straight. 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. April 2008 39 TIRE MATCH MOUNTING Your approach to match mounting will transition of the harder and softer sec- depend on several variables: tions of the tire may create a series of •whether the tire is runout- and harmonic vibrations as the various sec- weight-matched, tions of the tire contact and leave the •whether the wheel’s low runout spot road surface. Depending on conditions, can be determined, and this harmonic may occur once per tire •whether you have access to a load- revolution, or in a series of multiple vi- applying balancing machine. brations per revolution. It’s possible that Regardless of the specific approach this phenomenon may vary according to you take, it’s important to understand changes in tire pressure, vehicle speed, that “stacked-up” runout and imbalance individual tire load and road surface conditions can be addressed. Of course, conditions, all of which may serve to re- once tire matching has been accom- duce and/or amplify the vibration prob- plished, the mounted package must lem. In other words, the vibration the then be checked and corrected for dy- driver feels may not occur at any one namic balance. rate of speed, or on any particular road There are two types of radial runout A red dot on the tire indicates the surface, because the problem may ap- —static and dynamic. Static runout, as tire’s maximum point of radial runout. pear only under a specific combination we noted earlier, refers to the high A yellow dot indicates the tire’s point of these variables. spot of the tire, a physical characteris- of least weight. The conventional If a tire/wheel will not balance prop- tic that can be measured with no load thinking was that the tire’s red dot erly, or if a vibration exists after a suc- placed on the tire. Radial force varia- should be aligned to the wheel’s valve cessful balance job, don’t automatically tion, however, refers to a dynamic stem, since this should be the wheel’s blame the tire. If you haven’t checked runout condition, which occurs only point of minimum radial runout. How- the hub and wheel for runout, you may when the tire runs at speed, under ever, since some of today’s custom be jumping to conclusions. If, however, wheels feature the valve stem in a po- load, due to variations in construction sition that addresses appearance all balance, static runout and chassis stiffness. rather than runout or balance, it’s parts variables have been exhausted, Radial force variation is so named best to check for installed radial then it may be time to suspect a radial because the radius of the tire varies ac- runout on a wheel balancer that fea- force variation problem. cording to vehicle speed and load. Of tures a “road” wheel that exerts load- To check for and attempt to actually course, any tire, because of its pliability, ing pressure on the tire. verify a dynamic radial runout condi- will vary slightly in radius at the load tion, a spin-balancer with a built-in load spot during operation. Although a “ra- struction. Given the precise quality roller is recommended. This type of dial force” might be the result of a control processes used by today’s tire balance machine places a load (which runout area pronounced enough to af- makers, it’s rare that a force variation attempts to simulate road load) onto fect the tire’s impact on the road, a ra- problem will occur. But when it does, it the tire as it spins, while monitoring dial “force variation” may occur if the can be a tricky demon to chase. and recording variances of runout. If tire has appreciably different “soft” Even though no problems may be load variation is found, it may be cor- spots and “stiff” spots in the carcass found as the tire rotates on the balancer, rected to an acceptable level via balanc- and/or tread or in the sidewall con- when the tire experiences a load, the ing weights. In extreme cases, it may When installing a valve onto an alloy wheel (or painted steel wheel), be careful not to scratch or gouge the surface. If you’re using a lever-type valve installer (left photo), pad the tool to protect the rim edge. A cable straight-pull type valve installer (right) is a better choice, since it makes no contact with the wheel surface. 40 April 2008 TIRE MATCH MOUNTING verify that the tire should be finish and, more importantly, replaced.

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