Wheel Technical Information

[Gordon]

How to Measure Bolt Patterns



How to Measure Wheel BackSpace

Items required to measure wheel backspace:
- Tape measure
- Straight edge
- Wheel w/o tire (preferred)

The easiest way to measure backspace is to lay the wheel face down onto the ground so the backside of the wheel is facing up. Take a straight edge and lay it diagonally across the inboard flange of the wheel. Take a tape measure and measure the distance from where the straight edge contacts the inboard flange to the hub mounting pad of the wheel. This measurement is backspace. The above photo shows three wheels with 2",3", & 4" backspace.



Measuring Wheel Offset


To calculate offset you'll need the following measurements:
- Wheel backspace
- Wheel Width
- Wheel Center line (outboard flange to inboard flange measurement / 2)

Subtract:
Wheel center line from Wheel backspace to get offset.
- If backspace is less than the wheel centerline the offset is negative
- If backspace is greater than the wheel centerline the offset is positive

Tip:
- To convert from inches to mm multiply by 25.4
- To convert from mm to inches divide by 25.4



Backspace to Offset Conversion Chart

The table Above is quick reference for finding offset, pick the rim width and follow the row over to the backspace of your wheel.


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'll have to use the physical dimensions of the current wheel/tire package to determine the dimensions of the new wheel/tyre package.

Items which are potential trouble spots:
- Tie Rod Ends
- A-arms
- Brake Calipers
- Shocks and Shock Mounts
- Inner & Outer Fenders (esp. front tyres turned to lock)


In the drawing on the left, we've made two measurements
- Front Side Clearance
- Back Side Clearance

These measurements when used with:
- Tyre Section Width
- Tyre Diameter
- Rim Width
- Rim Backspace

Help determine if wheel/tyre clearance is adequate for the new wheel/tyre package you've selected


Determine Wheel Caliper Clearance

Ensuring proper caliper clearance inside the wheel is important. The following chart should enable you to have the dimensions required by most wheel manufactures.
A. Caliper Overhang Distance Used to determine if wheel dish is adequate (in some cases a spacer is 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



Typical Lug Nut Torque Specifications


Lug Size ------- Ft/Lbs Torque
7/16" ------------- 55-65
1/2" -------------- 75-85
9/16" ------------ 95-115
5/8" ------------- 135-145
12mm ------------- 72-80
14mm ------------- 85-95

IMPORTANT NOTICE: As with all types of wheels retorque lug nuts after the first 25 miles & at 100 mile intervals until lug torque is maintained.
Note: Always refer to Owner's Manual for proper factory specifications that take precedence over the listed recommendations.


Source:rsracing.com