To assure correct fitment, proper replacement
wheel size, dimension,
and load-carrying capacity are critical. Always consult the wheel
manufacturer/distributor's literature to verify that the desired
wheel and tire combination is an acceptable application for the
vehicle.
Wheel Width
Choosing the wheel's width is important
to assuring customer satisfaction. In addition to correct fitment,
the wheel's width also influences handling and ride quality. Always
choose a rim width within the range of the tire's acceptable rim
width specifications.
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Choosing a wider rim: increases
vehicular stability, steering response and cornering ability. A
rule of thumb is to use a rim width 90% as wide as the tread width
(not section width) of a performance tire for street applications.
This provides a good balance between performance and ride quality.
Always be sure that the chosen rim width is within the tire's range
of acceptable rim width specifications.
Choosing a narrow rim: results in an improvement in ride quality, but may sacrifice the tire's ultimate performance capabilities.
Choosing a mid-range rim width: provides a balance between handling capabilities and ride quality.
An example of a proper application would be to use a 15" x 6" wheel for a 205/70VR15 tire. Never attempt to mix millimetric wheels and tires with standard inch wheels and tires. An improper application would be mounting a 200/60R390 size tire on any 15" wheel. A 390mm tire is designed to fit on a wheel with a diameter of approximately 15.35" with a non-standard bead seat.
Warning:
According to RMA guidelines, there
is danger in installing a tire of one rim diameter on a rim of a
different rim diameter. Always replace a tire on a rim with another
tire of exactly the same rim diameter designation and suffix letters.
For example: a 16" tire goes with a 16" rim. Never mount a 16" size
diameter tire on a 16.5" rim. While it is possible to pass a 16"
diameter tire over the lip or flange of a 16.5" size diameter rim,
it cannot be inflated enough to position itself against the rim
flange. If an attempt is made to seat the tire bead by inflating,
the tire bead will break with explosive force and could cause serious
injury or death.
High Performance Wheels
The following are various high performance
wheel measurements that play an important role in determining tire
and wheel fitment:
Wheel Backspace
The distance from the back edge of the
wheel to the hub mounting surface. To determine the wheel backspace:
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Position the wheel face down.
Lay a straight-edge across the back of the wheel. Measure the distance from the straight-edge to the wheel's hub mounting surface.
Wheel Offset
The wheel's offset is the distance from
its hub mounting surface to the centerline of the wheel. The offset
of a wheel can be one of three settings:
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Zero offset: The hub mounting
surface is even with the centerline of the wheel.
Positive offset: The hub mounting surface is toward the front or wheel side of the wheel. Positive offset wheels are generally found on front-wheel drive cars.
Negative offset: The hub mounting surface is toward the back or brake side of the wheel's centerline. "Deep dish" wheels are typically negative offset. Offset can be calculated by positioning the wheel on a flat surface and measuring its overall width. Subtract the backspace, and divide by two.
Backspacing - (overall width divided by 2) = offset
Bolt Circle
When considering custom wheels for a
specific application, it is imperative that the wheel's bolt circle
matches that of the intended vehicle. The bolt circle is the diameter
of an imaginary circle formed by the centers of the wheel lugs.
The bolt circle reference is designed to accommodate 4-, 5-, 6-
and 8-lug patterns. A bolt circle marked 5-100 (Chevrolet Cavalier,
for example) indicates a 5-lug pattern with a diameter of 100mm.
Consult the rim manufacturer's literature for bolt circle information
for each application. If there is no information available, you
may need to calculate the bolt circle.
4-, 6-, or 8-lug patterns:
Record the distance between the
centers of two holes directly opposite one another.
5-lug pattern:
Estimate by measuring from the
center of one hole to the far side (outside, not center) of a non-adjacent
hole. The diagram below illustrates the proper measuring methods.
Hub-Centricity vs. Lug-Centricity
Another important consideration in the
proper selection of custom wheels is the concept of hub-centricity.
This refers to a situation where the center bore hole of the wheel
exactly matches the vehicle's hub diameter. In other words, if the
vehicle's hub diameter is 56mm (e.g., Acura Integra), the wheel's
center bore hole should be designed to match it perfectly.
Hub-centricity
When automobile manufacturers design
a vehicle, they utilize hub-centric wheels so that:
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The wheels are positioned very precisely
on the car.
The possibility of shifting while being mounted is minimized.
Lug-centricity
The alternative to a hub-centric wheel
is known as lug-centric.
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The wheels are located solely by the
lug nuts rather than
the wheel hub.
As the lug nuts are tightened, they adjust the wheel's position relative to the hub, thus centering the wheel.
Properly torqued, the lug nuts continue to keep the wheel centered as the vehicle is driven.
Lug-centric wheels require extra care in mounting on a vehicle. When using shouldered nuts instead of tapered nuts, take extra care to properly locate the wheel. Never use air tools to install high performance wheels! Always use a torque wrench and follow accepted tightening procedures
