Wheel Backspace and Offset Relationship
Offset (mm)
Rim's Tire Width (inch)
Backspace (inch)
Backspace and Offset Example

Wheel Offset to Backspace Calculator v1.00

Enter the Rim Tire Width on your wheel.
Then the Offset in Millimeters (mm). Offset can be POSITIVE or NEGATIVE.


Press CALCULATE to find other values. Hit RESET  to clear the form and SAMPLE if you want to see a sample calculation.

NEGATIVE offset number means the mounting flange is past the centerline of the rim towards the inside of the car.

POSITIVE offset number means the centerline of the flange is towards the outside of the rim.

ZERO offset  indicates the mounting pad centerline is dead center in the rim.

NOTE : This calculator takes into account for the rims outer lips which seem to be standard at 0.5" each. An 8" rim width measured from the tires perspective will yield a total width of the rim at 9".

AND OF COURSE USE AT YOUR OWN RISK, MEASURE TWICE OR MORE TO ENSURE CORRECT FITMENTS WHEN ORDERING RIMS!

Lastly the Cutaway of the wheel/rim would have 'NEGATIVE' offset since the mounting pad is inwards of the centerline.

Wheel Offset to Backspace Calculator


Well after you found you perfect set of rims you find that the number has an 'offset' instead of a 'backspace' number. It's easy to convert from one to the other so you can get the correct fitment for your wheels. Typically Backspace is measured in inches (in) and offset measured in Millimeters (mm).  If you need to convert from Backspace to Offset click - Backspace to Offset Calculator.

To Find the the backspace given the offset and rims tire size use this formula:

Backspace = (Rim's Tire Width + 1)/2 + (Offset/25.4)

Where-

Rim's Tire Width = Specified Tire Mounting Width for the rim, NOT the total rim width. The common practice is to add 1" to this, and the calculations above has it as well.

Offset
= The rims given Offset in Millimeters

Backspace
= The results in inches

CALCULATOR IS BELOW THE CUTAWAY IMAGE OF THE RIM

Negative Positive Offset Example
Wheel Offset Drawing
Measure Wheel Offset
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