What Is Match Mounting?

Home , Alloy wheel, Custom wheel, Radial Force Variation, Valve stem

dding performance vehicle owners to your customer list can give a huge boost to your shop’s bottom 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 location 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. the wheel will eventually A minimum range of be- loosen and wobble as it tween .3 and .5 oz. (7 to 14 moves in relation to the hub. grams) of imbalance is usual- Seat styles most common- ly enough for the average ly found include radius, coni- motorist to notice an imbal- cal and flat (“mag”). These ance-induced vibration. If a terms refer to the shape of vehicle is sensitive enough to the seat (where the fastener exhibit noticeable vibration contacts the entry of the fas- at only .3 to .5 oz. of imbal- tener hole in the wheel). ance, that same amount of Radius seats, also re- vibration may be present ferred to as ball seats, fea- with as little as 10 to 15 lbs. ture a ball shape that mates of radial force variation, into a wheel’s female ra- which (although hard to be- diused ball relief at the lieve) can be caused by as lit- wheel’s mounting hole. tle as .010 to .015 in. of If the custom alloy wheel is hubcentric, or if the wheel cen- Conical seats are also loaded radial runout. Using ter hole is oversized and requires a hubcentric adapter to called cone seats or tapered this as an example, it’s easy properly fit the vehicle hub, be sure to install the adapter seats. This seat style features to see how loaded runout onto the wheel or hub before installing the wheel. Always an angled seat wall. The fas- can dramatically affect vibra- check the wheel maker’s instructions to see if hubcentric tener features a male cone tion. In other words, a little adapters are required and/or included in the box. seat, the wheel a female bit of “loaded” tire runout cone entry hole. The most variance can produce a notable impact ening on the road, with the wheels dis- common seat taper angle is 60°. on operating smoothness or harshness. connecting from the hubs. A mag wheel nut features a flat con- The seat refers to the actual contact tact patch at the wheel (and usually a Handling Custom Wheels area between the fastener’s head and thick flat washer). A mag-style nut may It’s extremely important to pay attention the wheel. The seat style of the fastener also feature a smooth outer-walled ex- to wheel fastener seat styles. Make sure must match the seat style featured on tended shank that helps center the you use the correct style of wheel nut or the wheel. If the wrong seat style is wheel on a lugcentric design, as the bolt specified for the custom wheels at used, the wheel simply will not be fas- shank enters the wheel’s bolt hole and hand. Installing the incorrect seat style tened to the hub correctly. If the fasten- serves as a guide pin to center the can damage the wheel bolt hole seats; at er seat style does not match that of the wheel’s hole over the wheel stud. Using worst, it can result in the fasteners loos- wheel, you’ll likely damage the wheel a capped nut (where the threads do not

Check the back side of the wheel’s hub face to see if the bolt holes are chamfered or recessed to clear any OE hub or drum retainer clips. If they’re not, remove any existing clips (shown here). If the wheel’s hub mating Here, a hubcentric wheel adapter is installed onto the hub. If surface won’t clear these clips and the clips are left in your wheels require these center-hole-filler/locators, be place, the wheel won’t be able to mount flush to the hub, sure to install them. If you don’t, the wheel might not be cen- which will create an axial runout (wobble) condition. tered, which will result in radial runout (thumping, vibration).

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The wheel fastener seat style must match the seat style of the wheels to be installed. Shown here are (l. to r.): conical nut, conical nut with shank exten- sion, radius nut and wheel bolt featuring a radius seat. extend all the way through the nut) should be installed by tightening the may make it difficult to be certain that fasteners with a torque wrench only— the stud isn’t bottoming out inside the no exceptions. Using a torque wrench is nut. This is why it’s important to pay at- more time-consuming than using an tention to thread engagement length. impact gun, but the owner of a set of At a minimum, the nut must engage custom wheels expects the installation onto the stud at a depth equal to the to be performed correctly. stud diameter. For example, if the stud This brings us to the subject of impact diameter is 12mm, the nut must thread wrenches and torque sticks. Torque onto the stud by at least 12mm of sticks are basically little torsion bars with depth. Also, make sure the stud does a square drive at one end and a hex not bottom out inside the nut. If it socket at the opposite end. In theory, a does, it will be impossible to achieve torque stick should begin to twist (and full clamping load. thereby stop rotating the fastener) when When it comes to torquing the fas- a specified torque limit is reached. teners, make sure the threads are clean While the use of such a torque-limiting and free of dirt, grease, grit, etc. If burrs tool is better than nothing, the best and or flat spots are found, replace the fas- only proper method is to tighten all tener (both stud and nut). Fasteners are wheel fasteners with a hand-held torque intended to stretch slightly when fully wrench. Never use an impact wrench to tightened to specification. With regard tighten custom wheel fasteners. to automotive wheels, this creates the Always install any wheel, regardless correct preload required to secure the of what it’s made of, by tightening the wheel to the hub. If the wheel fasteners are undertight- ened, they’ll eventually loosen, resulting in the wheel being damaged or actually coming off the vehicle. If the fasteners are tightened excessively, the wheel stud or bolt can permanently stretch, fa- tiguing beyond its designed elastic range. Overtightening also can result in fastener failure or, at the very least, in great difficulty during future removal. Especially with today’s lightweight alloy wheels and sometimes light (and thin) Check your socket to make sure it rotor hats, severe vibrations under brak- fits the wheel, if the fastener is re- ing can occur if wheels are improperly cessed into the wheel center sec- tion. If the socket must dive into the or unevenly tightened. fastener hole, a thick-wall socket The only way to ensure correct might not fit, resulting in wheel clamping loads is by tightening all wheel damage. Always make sure the inner fasteners with a properly calibrated walls of the socket are clean, to torque wrench. Every custom wheel prevent damaging fastener finish.

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Aftermarket wheel fastener socket kits are available that feature plastic or soft aluminum protector caps de- Bead lubrication is important, especially when dealing signed to prevent damage to both the wheel and the with low-profile, stiff-sidewall performance tires that chrome-plated fasteners. Such kits can prove handy if are to be mounted on alloy wheels. For smooth installa- you perform custom wheel service on a regular basis. tion, use only lubes made for tire-mounting applications. fasteners in a crisscross pattern to pro- dures, you’ll avoid damage to the wheel Wheels are designed to center onto vide even clamping loads. Uneven tight- and will greatly minimize the chance of the vehicle hubs by one of two meth- ening can easily result in a distorted hub a comeback for a vibration complaint. ods—lugcentricity or hubcentricity. A or wheel, leading to vibration and brake Overtightening or uneven tightening lugcentric wheel relies on centering via pedal bounce complaints. can easily cause hub/rotor distortion, the fastener locations only. As the Pay attention to torque value accura- which will result in brake rotor distor- lugnuts (or wheel bolts) are tightened, cy. When you do use a torque wrench, tion. the wheel is centered onto the hub. This make the final pulls slowly and carefully, Following the initial installation, it’s requires precise location of both wheel creeping up onto the final value, or advisable to check and retorque all bolt holes and the fastener locations on “click.” By abruptly “slamming” the wheel fasteners after the vehicle has the hub. A hubcentric wheel is centered torque wrench, especially when using a been driven 25 to 50 miles. If the tech- onto the hub via the fit of the wheel cen- ratcheting wrench, you can easily tight- nician cannot perform this initial drive, ter hole at the hub face. The hub face en beyond the target value. make a point of instructing the cus- will feature a center lip that engages into By avoiding the use of an air wrench tomer to bring the vehicle back to the a recess on the wheel’s center hole. Hub- and following correct tightening proce- shop for a retorque. centric designs more precisely locate the

Today’s high-tech wheel changers offer nylon pusher Torque the wheel fasteners in the appropriate crisscross wheels that aid in bead seating, while eliminating direct pattern. This evenly spreads the clamping load across contact with the wheel itself. Make sure all changer con- the hub face, minimizing the chance of warping the rotor tact points are clean before placing the wheel. hub. Never use an impact gun to install alloy wheels.

46 April 2008 wheel onto the hub, to minimize the hub and new rings on the wheels, the differs from the OE (for example, chance for installed radial runout. wheels won’t mate flush to the hub, maybe the OE nuts require a 19mm In some cases, a hubcentric ring which will cause severe axial runout. Al- wrench, but the new fasteners might re- 11 adapter is used to attain a proper fit, ways check carefully. quire an 18mm or ⁄16-in. wrench), be since the wheels at hand may feature a If your wheels include either alu- sure to also include an appropriate- larger center hole. This makes the minum or plastic hubcentric ring sized socket and breaker bar to allow wheel adaptable to various hub center adapters, be sure to use them. Even if the aftermarket wheel to be removed fitments, by simply choosing the cor- you feel that the fasteners alone will during a roadside tire change. At least rect-width adapter rings. It’s possible center the wheel, the rings provide a make the customer aware of this, and that an old adapter ring has stuck to the closer-tolerance fit to the hub center offer the option of allowing him to pur- hub. If this ring is not the correct size and will allow you to better center the chase an appropriate socket and break- for the wheel, the wheel may not be wheel during tightening. er bar, or at least tell the customer that able to seat flush against the hub (if the Before a vehicle leaves the shop with he’ll need these tools. Otherwise, the new wheels are already sized for the a newly installed set of custom wheels, customer may be stuck at the side of a OE hub without a ring, or if the new do the customer a favor. Place one highway with no way to remove the af- wheels use a new ring). Always check wheel’s set of OE fasteners in a reseal- termarket wheel. the hub face flange diameter and the di- able plastic bag and store them in the And finally, before a vehicle leaves ameter of the wheel’s mounting face- vehicle (in the tool kit, next to the spare the shop, take a few extra minutes to hole to make sure they match before at- tire or jack, etc.). If the customer ever clean the wheels and tires. Remember, tempting to install the wheels. needs to install the OE spare in an the custom wheel customer is interest- The wheel must fit flush against the emergency, he’ll have the correct fasten- ed in appearance. Wipe off any finger- hub and be centered on it. If the wheel ers, since the fasteners that are used prints, smudges, etc., being careful not requires rings and none are used, you’ll with the aftermarket wheels may differ to scratch the wheel finish. have an off-center installation. If old in length or style from OE. Also, the OE rings are stuck to the hub, but the new lug wrench might not fit the new fasten- Visit www.motor.com to download wheels don’t need them, or if you try to ers, as the hex size may differ from OE. a free copy of this article. double-up old rings that are stuck to the If the new wheels’ fastener hex size

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