How To Measure An Axle

To measure an axle, you will need the following measurements: the face to face, mounting bracket centres (MBS) and the PCD.

Firstly, identify which type of axle you have. For short bracket axles they attach to the mudguard bracket, then to the chassis. For long bracket axles, these fix straight onto the chassis of the trailer. Once identified, measure the distance between the MBC. Then measure the face to face. These will give you all the measurements we need to find the right axle.

Load Capacity

The load rating of an axle must match that of the maximum gross weight. For twin axles, you must calculate the maximum gross weight and divide it by two to gather the minimum load rating.

Types of Axles:

There are predominantly two types of axles: spring axles and torsion axles.

Spring Axles – Spring axles function by using stacked metal leaf springs, either under or over the axle beam, to support the weight of the trailer.

Torsion Axles– Torsion axles work by using rubber cords or cartridges inside the axle tube to handle suspension travel and shock absorption. Torsion axles do not use leaf springs, but instead the compression of the rubber to supply the suspension support needed.

How To Measure A Bearing

If you need to measure a bearing, it is always best to check for the part number first. The part number is engraved onto most bearings and will give you the most accurate information. However, over time these can rub off and so it may be necessary to measure the bearing yourself.

To get the most accurate measurement you will need a vernier caliper, however, if you don’t have one available a ruler can also be used.

You will need to take three measurements, the inner diameter (ID), the outside diameter (OD) and the width (W). Bearings are often referenced to by these dimensions – ID x OD x W.

Types of Bearings:

Ball Bearing – A ball bearing uses loose balls to maintain separation between the two races.

Roller Bearing – The same as a ball bearing but instead of balls, a roller is used to maintain the separation, 

Needle Bearing – a small bearing which uses small rollers to reduce the friction between the races

How To Calculate PCD

What is pitch circle diameter (PCD)?

Pitch Circle Diameter (PCD) is the diameter of the circle that the wheel studs form.

How to calculate the PCD

Measure the distance between two adjacent studs (measure from the centre of the studs). Once you have this measurement, use the formulas below to calculate the PCD. The measurement between the two studs is indicated as ‘S’ in these formulas.


3 Stud PCD = ‘S’ / 1.155
4 Stud PCD = ‘S’ / 0.7071
5 Stud PCD = ‘S’ / 0.5878
6 Stud PCD = ‘S’ / 0.5
8 Stud PCD = ‘S’ / 2.613