Wheel measurements

We often find that some people are confused by wheel sizes when it comes to buying replacements. In this post I will explain what these measurements mean, and what to look out for when buying new wheels.

Trailer wheels are very similar, if not the same in some cases as car wheels. There are a lot of different wheels available, and as a trailer owner it would be useful to have some knowledge of them.

Wheel size

First of all you will need to know where everything is located and how to take some basic measurements of your wheels. The diagram below shows the basic layout of a wheel rim.

rim layout

The diagram below shows how you would measure the nominal diameter and inside width of the rim. This distance is most commonly measured in inches.


As you can see form the diagram above, the rim width is measured on the inside of the wheel. If the markings on the rim are still readable the width in inches will be followed by a letter J, then the diameter.

For example 4.5J13 means the inside width of the rim is 4.5″ and the Diameter is 13″.

There can be several pieces of information marked on a wheel rim. This could include:

  • The wheel manufacture. This should be marked on all wheels.
  • Bead type. This normally follows the wheel size.
  • Part number to get a direct replacement. Part numbers can sometimes be cross referenced in order to find similar wheels.

Other information that can be found may include:

  • Rim offsets.
  • Country of manufacture.
  • Date or date code.
  • Occasionally the manufacturer will give the PCD of the mounting holes.

The 3 most important measurements when looking for new wheels are the rim size, the PCD and the offset.
If you can get these measurements correct the wheel will fit.

Bead type

Beads are not really needed on smaller rims, therefore most small rims are manufactured without them. If your rim does have beads, the markings for each bead type and a description of each can be found below.

H – denotes one rounded bead on the outside of the rim.
H2 – denotes two rounded beads. The same as the image above.
FH – denotes a flat hump on the outside of the wheel
CH – denotes a combination of humps. One flat on the outside, and one rounded on the inside.
SL – these markings are used on wide wheels and mean ‘Special ledge’.

Generally in trailer wheels you will see a H, H2 or no bead at all.

Related posts:
Working out your PCD.
Trailer wheel offset.
Tyre speed ratings.
Tyre load index.

If you are looking to buy trailer wheels and tyres, choose from a large selection at Trailer Lights