Ask a Mechanic: Centering rings are important

Dear Ask a Mechanic,

I just bought a used set of four wheels for my 2017 Subaru WRX, but the seller only had two of the four centering rings. He said the other two were lost when he stored the wheels during winter, but that he still used them on his vehicles and that you don’t really need the rings anyway. Opinions from my friends and on online forums are divided about this. Are rings necessary? If they are, how do I figure out what I need? – Wheel driver

Will the wheels physically mount to the car and remain in place after being properly torqued, even without the missing rings? Yes, they will, however this is not how the manufacturer intends for the wheels to be mounted to the vehicle.

The raised central part of the vehicle’s hub flange – the part the wheel mounts to – is sometimes called the pilot, and it serves to both centre the wheel on the hub and provide additional load support for the wheel fasteners. Having the wheel accurately centered on the hub’s axis greatly reduces the likelihood of vibration from runout.

Consequently, I’ve yet to come across a factory wheel where the centre bore – the hole in the middle of the wheel – doesn’t directly correspond in size to the hub’s pilot.

Aftermarket wheels are a different story. Although there are numerous common bolt patterns, the diameter of the pilot usually varies between automakers (and even models). A manufacturer wanting to produce a wheel capable of fitting multiple different applications must make the bore big enough to fit different pilot sizes.

Unfortunately, this means it will be oversized for many pilots. This is where centering rings come into play. Made of either plastic or metal, they fit both the pilot and the wheel bore, filling the gap and locating the wheel properly on the hub.

Without that precise bore to pilot relationship, you’re relying on the taper of the nuts and bolts to line up the wheel on the hub, a job they were not intended for. Their purpose is to secure the wheel to the vehicle.

Factory bore sizes are often available online; all Subaru WRX’s use a 56.1 mm bore, for instance. You may find this number on the rings you do have. They may also have a pair of sizes in millimetres, and if the smaller number isn’t 56.1, the larger number should relate to the wheel’s bore. If it’s missing, but the wheel’s make and model is known, you may find the bore on the manufacturer’s website. Otherwise, accurate measuring tools will be required to determine what’s needed.

Correctly sized rings are relatively inexpensive and can be bought in stores or ordered online.  I’d strongly recommend using them.

Ask a Mechanic is written by Brian Early, a Red Seal-certified automotive technician. You can send your questions to wheels@thestar.ca. These answers are for informational purposes only. Please consult a certified mechanic before having any work done to your vehicle.