I want to change my car wheels size. Is it possible and what must I do?

car wheels size

You might want to change your car wheels size for various reasons. People usually choose bigger wheels for a sportier look. But some drivers want to switch to smaller wheels because they are more forgiving over bumps and improve the car’s ride.

Can you just bolt on a different car wheels size?

You could but they must conform to the car maker’s speed and load rating for that model. You will find these in your car’s user manual.

It’s also important to check the pitch circle diameter and offset. The pitch circle diameter is the distance on the car’s hub between the holes for the studs. Not all wheels are the same. Some might even have a different number of studs to others.

The offset is the difference between the mounting surface (the part of the wheel that meets the car’s hub) and the wheel’s centre line. Wheels with a negative offset have their mounting surface towards the back of the rim which gives the wheel a more dish-like effect. Those with a positive offset have their mounting point towards the front of the rim.

If you get the offset wrong, your new wheels might not fit under the wheel arches. And if they do, they might interfere with the suspension when you try to turn a corner.

car wheels size
This is an original Minilite wheel with a negative offset

The easiest thing to do…

…is to stick with the products offered by your car’s manufacturer. These are called Original Equipment and you’ll buy them from the manufacturer’s website or dealers. That way you can be certain they’ll fit your car.

Will different wheels improve your car’s ride and handling?

This is difficult to answer. According to tyre and wheel experts, no two sets of tyres and wheels are the same. One set of 18-inch wheels might weigh more than another set of identically sized rims.

How much does size matter?

Weight is as important as size. For starters, a lighter wheel means the suspension doesn’t have to work as hard. In turn it will make the car feel more agile as it will respond more immediately to what you do with the steering wheel. And if you consider a 2.5kg weight saving per wheel means a 10kg saving overall, it’s reasonable to assume lighter wheels will mean you’ll use less fuel.

car wheels size
Of all the wheels in all the world… There’s an almost endless choice of wheels but not all will be suitable, even if they are the size you want

Do you have to change your instruments?

A larger wheel will need fewer rotations to cover the same distance as a smaller one. That means if you replace wheels with a larger size, the speedo will read slower than you’re actually doing. It’s the opposite if you go from larger to smaller wheels. Therefore swapping wheels will mean you’ll have to have your speedo and odometer professionally recalibrated.

And tell your insurer

You must speak to your insurer if you modify your car and that includes putting non-standard wheels on it. The Association of British Insurers says insurers probably won’t charge you any extra. But you must at least tell them. This is so they can assess whether the new wheels pose any extra risk, either in safety, performance or theft terms.