How to measure trailer wheel bolt pattern – guide and table
The bolt pattern – also known as PCD (Pitch Circle Diameter) – describes the diameter of the circle on which the wheel bolts are arranged. It is written in the format number of bolts × diameter in mm, for example 4×100 or 5×112. Choosing wheels or rims with the correct bolt pattern is essential for safe and secure fitting.
Why does the bolt pattern matter?
The bolt pattern determines which rims and wheels will fit your trailer hub. If the bolt pattern does not match, the wheel cannot be mounted correctly – or worse, it may appear to fit but come loose during use. Along with the bolt pattern, the centre bore, offset (ET), and bolt thread size must also match your trailer’s specifications.
How to measure the bolt pattern on a trailer
The measuring method depends on how many bolts your wheel has:
4 or 6 bolts: Measure from the centre of one bolt to the centre of the bolt directly opposite. This measurement is the PCD.
5 bolts: Measure from the centre of one bolt to the outer edge of the bolt directly opposite. This gives the PCD for a 5-hole pattern. Alternatively, measure the distance between two adjacent bolts and convert using a multiplication factor of 1.701.
Common trailer bolt patterns
4×100 – common on smaller, lighter trailers
5×112 – widely used on mid-size trailers and caravans
5×120 – found on certain axle types and manufacturers
Always verify the bolt pattern against your trailer’s documentation or measure directly from the hub, as specifications vary between manufacturers and axle types.
What is the difference between bolt pattern, centre bore and wheel bolts?
The bolt pattern describes the arrangement of the fixing points. The centre bore is the hole in the middle of the rim that centres it on the hub. The wheel bolts clamp the rim to the hub. All three must be correct for a safe and proper fit. Fitting a rim with the wrong centre bore can cause vibration even if the bolt pattern matches.
What else affects which wheels fit your trailer?
Beyond the bolt pattern, you need to check the rim diameter and width, the centre bore size, the offset (ET value), and the bolt thread size and length. If any of these are wrong, the wheel may not sit flush against the hub or may foul the brake components. Incorrect offset in particular can affect how load is distributed across the wheel bearings.
Common mistakes when checking bolt pattern
– Measuring incorrectly on 5-bolt wheels (using the wrong reference points)
– Confusing bolt pattern with centre bore diameter
– Fitting rims that match the bolt pattern but have the wrong offset or centre bore
– Not checking the manufacturer’s specifications before ordering
Summary
The bolt pattern is one of the key measurements when selecting wheels or rims for your trailer. Measure carefully using the correct method for your number of bolts, and always cross-check against the manufacturer’s data. A correct fit protects the hub, the wheel bearings, and ensures safe handling on the road.