How do I determine Backspace and Offset?

Backspace is the distance in inches from the edge of the rear flange to the mounting pad.

Offset is the distance in millimeters from the wheel's imaginary centerline to the mounting pad.

  1. Gather the necessary tools:

    • Tape measure or ruler (preferably in inches)
    • Straightedge or long, flat object (e.g., a level or ruler)
    • Pen or marker
    • Safety glasses (optional but recommended)
  2. Prepare the wheel:

    • Ensure the vehicle is on a level surface and the wheel you want to measure is removed.
    • Clean the backside of the wheel to make measurements more accurate.
  3. Measure backspacing:

    • Place the wheel face down on a flat surface, making sure the backside is facing up.
    • Take the straightedge or long, flat object and align it across the backside of the wheel, spanning from the mounting surface to the inner edge.
    • Hold the straightedge in place firmly, ensuring it remains level.
    • Use the tape measure or ruler to measure the distance between the mounting surface and the inner edge of the wheel. This measurement is the backspacing.
  4. Calculate the offset:

    • To calculate the offset, you'll need the wheel width and backspacing measurement.
    • Divide the wheel width by 2.
    • Convert the offset to millimeters by multiplying it by 25.4 (since most wheel specifications are given in millimeters).
    • Subtract half the wheel width (converted to millimeters) from the backspacing measurement.
    • The result is the offset in millimeters. If you want to convert it back to inches, divide the offset by 25.4.

Note: If you already know the offset and want to determine the backspacing, you can reverse the calculation mentioned in step 4.

It's important to note that accurate measurements are crucial, and it's always a good idea to repeat the process a couple of times to ensure consistency. Additionally, when measuring wheels with complex designs or protruding features, such as spokes, consider measuring from the innermost point of the wheel.


Here's a handy offset to backspace conversion chart:



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