A
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
job done exactly the way they want it.
Some of the most common types of
work done on performance vehicles involve 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, essentially—tire match mounting and custom
wheel handling. Since you’ll never
mount a wheel without a tire, we’ll cover the ins and outs of tire match
mounting first.
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 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
38
April 2008
Photos: Mike Mavrigian
What Is Match Mounting?
TIRE MATCH
MOUNTING
& CUSTOM
WHEEL
HANDLING
B
BY
Y M
MIKE
IKE M
MAVRIGIAN
AVRIGIAN
Some of the most common types
of work done on performance
vehicles involve the wheels and
tires. This overview of tire and
wheel-handling procedures
provides information
you’ll need to keep
your customers
rolling smooth
and straight.
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 tire’s
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 minimize 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.
April 2008
39
TIRE MATCH MOUNTING
Your approach to match mounting will
depend on several variables:
•whether the tire is runout- and
weight-matched,
•whether the wheel’s 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 tire’s 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 con-
A red dot on the tire indicates the
tire’s maximum point of radial runout.
A yellow dot indicates the tire’s point
of least weight. The conventional
thinking was that the tire’s red dot
should be aligned to the wheel’s valve
stem, since this should be the wheel’s
point of minimum radial runout. However, since some of today’s custom
wheels feature the valve stem in a position that addresses appearance
rather than runout or balance, it’s
best to check for installed radial
runout on a wheel balancer that features a “road” wheel that exerts loading pressure on the tire.
struction. Given the precise quality
control processes used by today’s tire
makers, it’s rare that a force variation
problem will occur. But when it does, it
can be a tricky demon to chase.
Even though no problems may be
found as the tire rotates on the balancer,
when the tire experiences a load, the
transition of the harder and softer sections of the tire may create a series of
harmonic vibrations as the various sections of the tire contact and leave the
road surface. Depending on conditions,
this harmonic may occur once per tire
revolution, or in a series of multiple vibrations per revolution. It’s possible that
this phenomenon may vary according to
changes in tire pressure, vehicle speed,
individual tire load and road surface
conditions, all of which may serve to reduce and/or amplify the vibration problem. In other words, the vibration the
driver feels may not occur at any one
rate of speed, or on any particular road
surface, because the problem may appear only under a specific combination
of these variables.
If a tire/wheel will not balance properly, or if a vibration exists after a successful balance job, don’t automatically
blame the tire. If you haven’t checked
the hub and wheel for runout, you may
be jumping to conclusions. If, however,
all balance, static runout and chassis
parts variables have been exhausted,
then it may be time to suspect a radial
force variation problem.
To check for and attempt to actually
verify a dynamic radial runout condition, a spin-balancer with a built-in load
roller is recommended. This type of
balance machine places a load (which
attempts to simulate road load) onto
the tire as it spins, while monitoring
and recording variances of runout. If
load variation is found, it may be corrected to an acceptable level via balancing 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
finish and, more importantly,
verify that the tire should be
replaced.
the wheel will eventually
A minimum range of beloosen and wobble as it
tween .3 and .5 oz. (7 to 14
moves in relation to the hub.
grams) of imbalance is usualSeat styles most commonly enough for the average
ly found include radius, conimotorist to notice an imbalcal 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 fasat only .3 to .5 oz. of imbaltener hole in the wheel).
ance, that same amount of
Radius seats, also revibration may be present
ferred to as ball seats, feawith as little as 10 to 15 lbs.
ture a ball shape that mates
of radial force variation,
into a wheel’s female rawhich (although hard to bediused ball relief at the
lieve) can be caused by as litwheel’s mounting hole.
tle as .010 to .015 in. of
Conical seats are also
If the custom alloy wheel is hubcentric, or if the wheel cenloaded 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 fascan 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°.
connecting from the hubs.
on operating smoothness or harshness.
A mag wheel nut features a flat conThe 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 exto 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
surface won’t clear these clips and the clips are left in
place, the wheel won’t be able to mount flush to the hub,
which will create an axial runout (wobble) condition.
42
April 2008
Here, a hubcentric wheel adapter is installed onto the hub. If
your wheels require these center-hole-filler/locators, be
sure to install them. If you don’t, the wheel might not be centered, which will result in radial runout (thumping, vibration).
TIRE MATCH MOUNTING
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 extension, radius nut and wheel bolt featuring a radius seat.
extend all the way through the nut)
may make it difficult to be certain that
the stud isn’t bottoming out inside the
nut. This is why it’s important to pay attention to thread engagement length.
At a minimum, the nut must engage
onto the stud at a depth equal to the
stud diameter. For example, if the stud
diameter is 12mm, the nut must thread
onto the stud by at least 12mm of
depth. Also, make sure the stud does
not bottom out inside the nut. If it
does, it will be impossible to achieve
full clamping load.
When it comes to torquing the fasteners, make sure the threads are clean
and free of dirt, grease, grit, etc. If burrs
or flat spots are found, replace the fastener (both stud and nut). Fasteners are
intended to stretch slightly when fully
tightened to specification. With regard
to automotive wheels, this creates the
correct preload required to secure the
wheel to the hub.
If the wheel fasteners are undertightened, 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, fatiguing 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)
rotor hats, severe vibrations under braking can occur if wheels are improperly
or unevenly tightened.
The only way to ensure correct
clamping loads is by tightening all wheel
fasteners with a properly calibrated
torque wrench. Every custom wheel
44
April 2008
should be installed by tightening the
fasteners with a torque wrench only—
no exceptions. Using a torque wrench is
more time-consuming than using an
impact gun, but the owner of a set of
custom wheels expects the installation
to be performed correctly.
This brings us to the subject of impact
wrenches and torque sticks. Torque
sticks are basically little torsion bars with
a square drive at one end and a hex
socket at the opposite end. In theory, a
torque stick should begin to twist (and
thereby stop rotating the fastener) when
a specified torque limit is reached.
While the use of such a torque-limiting
tool is better than nothing, the best and
only proper method is to tighten all
wheel fasteners with a hand-held torque
wrench. Never use an impact wrench to
tighten custom wheel fasteners.
Always install any wheel, regardless
of what it’s made of, by tightening the
Check your socket to make sure it
fits the wheel, if the fastener is recessed into the wheel center section. If the socket must dive into the
fastener hole, a thick-wall socket
might not f it, resulting in wheel
damage. Always make sure the inner
walls of the socket are clean, to
prevent damaging fastener finish.
TIRE MATCH MOUNTING
Aftermarket wheel fastener socket kits are available
that feature plastic or soft aluminum protector caps designed to prevent damage to both the wheel and the
chrome-plated fasteners. Such kits can prove handy if
you perform custom wheel service on a regular basis.
fasteners in a crisscross pattern to provide even clamping loads. Uneven tightening can easily result in a distorted hub
or wheel, leading to vibration and brake
pedal bounce complaints.
Pay attention to torque value accuracy. When you do use a torque wrench,
make the final pulls slowly and carefully,
creeping up onto the final value, or
“click.” By abruptly “slamming” the
torque wrench, especially when using a
ratcheting wrench, you can easily tighten beyond the target value.
By avoiding the use of an air wrench
and following correct tightening proce-
dures, you’ll avoid damage to the wheel
and will greatly minimize the chance of
a comeback for a vibration complaint.
Overtightening or uneven tightening
can easily cause hub/rotor distortion,
which will result in brake rotor distortion.
Following the initial installation, it’s
advisable to check and retorque all
wheel fasteners after the vehicle has
been driven 25 to 50 miles. If the technician cannot perform this initial drive,
make a point of instructing the customer to bring the vehicle back to the
shop for a retorque.
Today’s high-tech wheel changers offer nylon pusher
wheels that aid in bead seating, while eliminating direct
contact with the wheel itself. Make sure all changer contact points are clean before placing the wheel.
46
April 2008
Bead lubrication is important, especially when dealing
with low-profile, stiff-sidewall performance tires that
are to be mounted on alloy wheels. For smooth installation, use only lubes made for tire-mounting applications.
Wheels are designed to center onto
the vehicle hubs by one of two methods—lugcentricity or hubcentricity. A
lugcentric wheel relies on centering via
the fastener locations only. As the
lugnuts (or wheel bolts) are tightened,
the wheel is centered onto the hub. This
requires precise location of both wheel
bolt holes and the fastener locations on
the hub. A hubcentric wheel is centered
onto the hub via the fit of the wheel center hole at the hub face. The hub face
will feature a center lip that engages into
a recess on the wheel’s center hole. Hubcentric designs more precisely locate the
Torque the wheel fasteners in the appropriate crisscross
pattern. This evenly spreads the clamping load across
the hub face, minimizing the chance of warping the rotor
hub. Never use an impact gun to install alloy wheels.
wheel onto the hub, to minimize the
chance for installed radial runout.
In some cases, a hubcentric ring
adapter is used to attain a proper fit,
since the wheels at hand may feature a
larger center hole. This makes the
wheel adaptable to various hub center
fitments, by simply choosing the correct-width adapter rings. It’s possible
that an old adapter ring has stuck to the
hub. If this ring is not the correct size
for the wheel, the wheel may not be
able to seat flush against the hub (if the
new wheels are already sized for the
OE hub without a ring, or if the new
wheels use a new ring). Always check
the hub face flange diameter and the diameter of the wheel’s mounting facehole to make sure they match before attempting to install the wheels.
The wheel must fit flush against the
hub and be centered on it. If the wheel
requires rings and none are used, you’ll
have an off-center installation. If old
rings are stuck to the hub, but the new
wheels don’t need them, or if you try to
double-up old rings that are stuck to the
hub and new rings on the wheels, the
wheels won’t mate flush to the hub,
which will cause severe axial runout. Always check carefully.
If your wheels include either aluminum or plastic hubcentric ring
adapters, be sure to use them. Even if
you feel that the fasteners alone will
center the wheel, the rings provide a
closer-tolerance fit to the hub center
and will allow you to better center the
wheel during tightening.
Before a vehicle leaves the shop with
a newly installed set of custom wheels,
do the customer a favor. Place one
wheel’s set of OE fasteners in a resealable plastic bag and store them in the
vehicle (in the tool kit, next to the spare
tire or jack, etc.). If the customer ever
needs to install the OE spare in an
emergency, he’ll have the correct fasteners, since the fasteners that are used
with the aftermarket wheels may differ
in length or style from OE. Also, the OE
lug wrench might not fit the new fasteners, as the hex size may differ from OE.
If the new wheels’ fastener hex size
differs from the OE (for example,
maybe the OE nuts require a 19mm
wrench, but the new fasteners might require an 18mm or 11⁄16-in. wrench), be
sure to also include an appropriatesized socket and breaker bar to allow
the aftermarket wheel to be removed
during a roadside tire change. At least
make the customer aware of this, and
offer the option of allowing him to purchase an appropriate socket and breaker bar, or at least tell the customer that
he’ll need these tools. Otherwise, the
customer may be stuck at the side of a
highway with no way to remove the aftermarket wheel.
And finally, before a vehicle leaves
the shop, take a few extra minutes to
clean the wheels and tires. Remember,
the custom wheel customer is interested in appearance. Wipe off any fingerprints, smudges, etc., being careful not
to scratch the wheel finish.
Visit www.motor.com to download
a free copy of this article.
Circle #21
April 2008
47