How to measure your axle length

Axle Dimension Clarification

How to measure your axle
 Dimension Name Description
TT Tip to Tip Total length of axle from end to end
FF Face to Face Distance from one wheel face to the other (track width)
CW Chasis Width Distance between outside of chasis rails
CF Chasis to Face Distance from ourside of chasis rail to wheel face
TC Tyre Clearance Distance between outside of chasis rail to inside wall of tyre
AS Axle Section Steel section of axle (45 square, 50 rounds, etc)
TW Tread Width Tread width of tyre
BS Back Space Distance from inside tyre wall to wheel face


Axle Selection
Before selecting an axle, you will need to decide on the following:

  • Trailer ATM / GTM
  • Single or Tandem axle
  • Choice of brake type
  • Type size and stud pattern

Based on this information, you will now have a minimum axle section, hub / disc / drum size, bearing size and axle length for your trailer.

FF = CW + (2 x TC) + (2 x BS)

TC is minimum 45 mm
BS is measured or calculated from tyre size

For a CW of 1200mm, Tyre size 205/75R15 (no offset),

FF = 1200 + (2 x 45) + (205) = 1495mm