Wheel Tech & Fitment

Fitment Guides

Determining Vehicle Fitment

Fitting a wheel and tire package is different for each vehicle, but by following these guidelines your chances for success will be much greater.  In most cases you can use the physical dimensions of the current wheel and tire assembly to determine the dimensions of the new wheel and tire package.

Measuring Wheel Backspacing

The easiest way to measure the backspace of a wheel is to lay the wheel face down on a smooth surface so the backside of the wheel is facing upward. Take a straight edge and lay it diagonally across the inboard flange of the wheel.

Use a tape measure to measure the distance from somewhere on the straight edge directly downward to the hub mounting pad of the wheel. Your measurement will be the backspace in inches. See photo showing three wheels with 2″,3″, and 4″ backspace measurements.

Determining Wheel Caliper Clearance

A – Caliper Overhang Distance: Used to determine if wheel dish is adequate (in some cases, a spacer may be required for clearance

B – Diameter of Hub Center: Required if wheels are hub centric

C – Wheel Stud Diameter: Required along with bolt circle

D – Height of Hub Center

E – Length of Lug and Thread Type (Fine or Coarse): Required to determine if longer studs are necessary

F – Distance from CL of Hub to Caliper: Used with A to determine if a spacer is required for proper fitment

G – Width of Caliper: Used with F to determine if wheel ID is adequate to clear rotor/caliper package

H – Diameter of Hub Mounting Face: Used to determine if hub is adequate to support wheel/spacer

Wheel Terminology

Axle Pad or Hub Flange:
The area of a wheel where it contacts a car.

Bolt pattern or lug pattern or bolt circle:
These refer to the number of fasteners (lug studs) and diameter of the circle on which they are positioned. (5x4.5” would be “five by four and one-half.”)

Outer Rim:
The outermost part of a wheel. It is the area where a tire is mounted.

Center Cap:
The wheel part that covers the center bore of the wheel on the outer face of the wheel.

Wheel Center:
The portion of a wheel that consists of the axle mounting pad and the spokes.

Drop Center:
Is the smallest inside diameter area of the outer barrel of a wheel. It is used to facilitate the installation of a tire onto a wheel. Additionally, it is used as an area for placing a center disc for some 2-piece wheels during the manufacturing process.

Back Space or Rear Space:
The distance from the axle pad to the outer most edge on the backside of the wheel. 

Front Space:
The distance from the axle pad to the outer most edge on the frontside of the wheel. 

Hub Diameter or Center Bore:
This is the size of the hole in the center of a wheel.

The distance +/- from wheel centerline, indicated in millimeters.

Negative Offset:
When the axle pad of the wheel is closer to the inner (car underside) edge plane.

Positive Offset:
When the axle pad of the wheel is closer to the outer (street side) edge plane.

Zero Offset:
A situation when both the back spacing and front spacing are equal. The axle flange is centered between the outer edge plane and inner edge plane.

Wheel Stud or Lug Stud or Axle Bolt:
The “BOLT” portion of the wheel-fastening device. It is what the “lug nut” threads onto.

Lug Nut or Wheel Nut:
The “NUT” portion of the wheel-fastening device. It treads onto a lug stud.

Wheel Size:
The portion of the wheel that reflects what size tire it can accomidate. Not the overall size of the wheel. Usually used when talking about a wheel size. (15x7”, 16x8”, 17x7”, Etc.)

All wheels will measure appx. 1" wider than their stated width.
For example, a 8" wide wheel with 4" backspace, will have a frontspace of 5".