Quik-Link: 800-687-1557 ext. 15107
amount, and that might
already be only a few milli-
meters. If the OEM wheels
have a positive offset, you
can safely install wheels with
even more positive offset
and use spacers to move the
contact patch out to its orig-
inal position, keeping scrub
radius the same. Just make
sure the new wheels and tires
ft inside the fender without
rubbing anything.
If the new wheels have
n e g a t i v e o f f s e t , t h e r e 's
nothing you can do to move
the contact patch in toward
the center of the car. The
only way to know for sure
how much the new offset will
affect scrub radius is to put
the car on an alignment rack.
A few fnal details
Even if you're confdent the
wheels have been properly
selected for the vehicle, it's
up to your technician to make
sure everything fts properly.
It's a good idea to test-ft the
wheel onto the front and rear
hubs before mounting the tire.
The frst thing to check is brake
caliper clearance: On OEM
wheels it might be as small as
1/8 of an inch (4 mm). This can
be hard to see, but it's easy to
simply install the bare wheel
and turn it by hand. If clear-
ance is that tight, the tech must
take extra care when placing
the wheel weights.
Mounting a tire on an after-
market wheel versus an OEM
wheel may be different; it
depends on the location of the
wheel's drop center. Usually
the drop center is toward the
outside of the wheel, so the
wheel is placed outside-up
on the tire changer. But some
aftermarket wheels have the
narrowest part of the drop
center toward the inside of the
wheel. These must be placed
on the tire machine inside-
up. If not, the machine will try
to stretch the bead — which
can't stretch — and that can
damage the wheel, the tire, the
tire machine or the technician.
Finally, make sure your techs
tighten the lug nuts with a prop-
erly calibrated torque wrench
every single time! Uneven lug
nut torque is almost guaranteed
to cause warped brake rotors
within a few thousand miles.
Finally, remind your customers
to come back after five to 50
miles to get re-torqued. ■
Jacques Gordon has worked
in the automotive industry
for 40 years as a service
technician, lab technician,
trainer and technical writer.
He began his writing career
writing service manuals at
Chilton Book Co., and writes
for Modern Tire Dealer's sister
publication, Auto Service
Professional. He currently
holds ASE Master Technician
and L1 certifications and
has participated in ASE test
writing workshops.
The distance from the hub fange to the straight edge is the last measurement needed to determine
offset. If that number is smaller than your centerline calculation, offset is positive.
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