How to Measure Wheel Backspace on a Caravan
Caravan & Trailer Tips
Wheel backspace is a critical measurement for caravan safety and performance. In fact, it is so important that custom axle manufacturers like Couplemate will not build a new axle without this exact figure.
An incorrect backspace causes the tyres to rub against the caravan chassis or inner guards. This leads to friction, tyre blowouts, and severe structural damage.
Here is a step-by-step guide to accurately measuring your wheel backspace.
What is Wheel Backspace?
Backspace is the distance from the innermost edge of the wheel rim to the flat mounting face of the wheel centre (the hub face). It determines how deep the wheel sits inside the caravan wheel arch and how much clearance remains between the tyre and the chassis.
Tools You Need
- A straightedge (a rigid steel ruler or timber piece long enough to span the tyre
- A tape measure or a second ruler.
- A flat, level surface
Step-by-Step Measurement Guide
- For the most accurate results, measure the wheel with the tyre fully inflated.
- Remove the wheel: Jack up your caravan safely, secure it on chassis stands, and remove the wheel assembly.
- Lay the wheel flat: Place the wheel face-down on a smooth, non-scratch surface so the back of the wheel faces upward.
- Position the straightedge: Lay your straightedge flat across the tyre sidewall or the very back edge of the wheel rim.
- Measure the drop: Insert your tape measure straight down from the underside of the straightedge to the flat mounting face where the wheel meets the brake drum or lazy hub.
Record the measurement: Write down this figure in millimetres. This total distance is your wheel backspace.
Key Tips for Accuracy
- Measure to the mounting face: Do not measure to the bolt holes or the centre bore lip.
- Measure exactly to the flat surface that presses against the axle hub.
- Keep it square: Ensure your tape measure is perfectly vertical (90 degrees) to the straightedge to avoid over-calculating the distance.
- Account for tyre bulge: If your tyre bulges out past the rim, your straightedge must rest on the tyre bulge. This ensures you calculate true chassis clearance.