You don’t have to look too far to hear tales of broken wheel studs, and loose wheel nuts… sometimes with dramatic aftermath! What’s the cause? There’s a few. Let’s look at how to prevent broken caravan wheel studs and loose nuts.
Just because one or all of your wheel studs break, doesn’t prove that the studs were at fault. The cause could be one of many. Wheels ain’t wheels, to bastardise the old Valvoline oil ad and come with instructions that need to be precisely followed. It’s vital to ensure that if you, a dealer or a previous owner fit aftermarket wheels and nuts, they thoroughly check to make sure the replacement wheels and nuts are, in fact, entirely suitable for the vehicle and axles. And we don’t mean that they suit ‘the look you’re going for’.
Despite offers of help, our friend here in the video was going to get himself home.
So, what are the possible reasons for broken wheel studs, or loose – and lost – nuts? Tyre shop! Rattle gun! I can hear the cries from the cheap seats – well, yes, but there’s much more to consider. Let’s look at what that might be.
- The pitch circle (see below) of the studs in the (imperial) hub are not exactly the same as that of the holes in some (metric) wheels, such that all studs bend when the nuts are tightened.
- The angle of the taper on the nuts not the same as the angle of taper in the wheels.
- The use of low-grade steel studs.
- The hole in the wheel centre is not compatible with the spigot diameter of the hub.
- The serrated studs not fully driven home when pressed into the hubs, such that they gradually ‘give a little’, causing the nuts to become loose.
- Rattle guns – set at unknown high-torque levels – used to tighten wheel nuts (rather than just undo them), causing the studs to stretch, and thus become weakened
- Nuts being tightened in a circular pattern in one action, rather than in a criss-cross or star pattern, using two or three (increasing) torques.
- Wheel centres being highly dished, thus acting as a large spring-washer that gradually loses its tension and causes the nuts to loosen.
All nuts must be tightened to the correct torque, and in the correct pattern, in strict accordance with the instructions provided by the wheel or chassis manufacturer.
It is strongly recommended that visible lines are made on one face of each nut – with a mating line on the wheel – so that a quick visual inspection can detect any loosening of a nut. Clip-on plastic indicators fitted to each nut, with their adjacent arrow-heads aligned provide an even-quicker warning of any nut loosening.
Continual vibrations and occasional large impacts from the road surface, inevitably have an adverse effect on the wheel assemblies, which is severely aggravated if the tyre pressures and the spring rates are too high for the actual wheel loading. These stresses on the wheel assemblies are increased further if shock absorbers are not fitted. Leaf-springs provide some damping of vibrations, but unfortunately, it is mainly on the ‘bump’ (upwards) movement of the wheel, rather than on the ‘rebound’ (downwards) movement of the wheel where it would be far more beneficial.
Matching rims to hubs
Caravans and trailers may have any type of wheel rim fitted. It’s vital to identify it correctly if you are getting spare parts. The team at Caravans Plus put together this guide. Hubs can be braked or non-braked, and they attach your rim to the axle. The number of studs and the stud pattern is the first thing to define.
Above: The PCD stands for Pitch Circle Diameter and goes through the centre of the studs. All our six-stud wheels have a PCD of 139.70mm (5 1/2″).
Above: For five studs we recommend the Adjacent Stud measurement, measured from the centres of the studs.
The table above shows measurements to define the rim. You only need to match either the PCD or the Adjacent dimension, whichever is easier to measure. The common hubs and rims are shown in the table with the Ford highlighted. Some measurements are shown as imperial as they are exact, the metric sizes for what you need to measure. The rim size is also needed to match the tyre size.
The cutaway rim above shows where the size is always measured in inches and it is measured where the rubber on the tyre fits on the shoulder of the rim. The width is measured between the shoulders as shown in the diagram.
As you can see there’s more to wheel fitment than you may have thought. So the next time you see a photo or video on social media where some unfortunate soul has come a cropper it may remind you to check your own. Have a think; when was the last time you checked yours?
Credits: Images Chris Ersek. Thanks to the Caravan Council of Australia and Caravans Plus.