How to measure Rim and Tyre Backspace

Wheel backspace is an essential measurement for the manufacture of axle length. RIM and Tyre PCD are also necessary features to convey when ordering a braked axle kit.

Click this link to read an excellent article on rim and tyre P.C.D.

Backspace is so essential, Couplemate will not manufacture a new axle without this measurement.

The first thing you need to do when building a new trailer is to buy your rims and types.

Alternatively, purchase your rims and tyres from us, and we’ll do the calculation for you. One more complication, we need to know your chassis width.

Step by Step procedure

  • Lay the tyre flat on the ground.
  • Zero offsets is the middle of the rim. A positive wheel offset is closer to the outside of the tyre whereas; a negative offset is closer to the chassis of the trailer.
  • Place the straight edge (ruler or timber) across the top of the type on the ground. Measure from the ground to the flat edge. This measurement is the width of the tyre.
  • Now measure the distance from the flange to the straight edge again. (the wheel sits on the mounting flange)
  • This measurement is your backspace (negative offset).
  • Backspace – tyre width is your front width or distance from the flange to the outside of your tyre (positive offset).