Can I Change My Tyre Size?

Every car, when it rolls off the factory floor, comes with a recommended tyre size based on the rims that the manufacturer fitted to it. If you were to replace those rims, you could technically change the size of the tyres within a certain range (essentially until they get too close to the wheel arches to operate safely). Doing so, however, also means you’ll have to have your speedometer recalibrated. 

But what if you don’t want to swap your rims? Could you get away with putting a different size tyre on your car? 

Well, yes and no. Let’s take a look at when you can and can’t change your tyre size.

Always avoid mismatched tyre sizes

Any reputable garage would refuse to fit a tyre that’s a different size than the rest of the set, but some might try to pass off a “close enough” tyre. And this becomes especially tempting if, for example, you’ve picked up a puncture after having just had a brand new set of premium tyres fitted. It may seem like the “close enough” tyre will actually be good enough and save you a bit of money – but, like with part worns, it’s a false economy. 

We’ll get onto mismatching tyres more generally in a moment, but having one tyre that’s a different size than the rest of the set will mean that your car sits and drives in a lopsided way. Think about wearing a stiletto on one foot and a plimsoll on the other – you’re likely to have quite a hard time getting anywhere in a hurry! 

Essentially, even if you decide to opt for tyres from a more budget-conscious brand, you need to make sure that the dimensions of the tyre match the rest of the set in order to be able to drive safely. 

Pitfalls to consider when fitting mismatched tyres

Many tyre experts, including Continental, strongly recommend fitting four of the same tyres to your car. By “same” they’re referring to the same size (whichever’s the correct size for your vehicle), the exact same tread pattern, and, ideally, the same age. They don’t suggest this because they want to sell more tyres - they do so because it’s proven to be much safer for drivers, their passengers, and other road users. And, in fact, fitting a complete set of premium tyres tends to mean you have to buy fewer in the long run.

If you ignore this advice, you’re exposing yourself to various problems:

1. Inaccurate speed ratings

Your speedometer works by measuring how fast your wheels are turning and converting that into a speed reading. Mismatched car tyres therefore have a habit of throwing off your speedometer, because the wheels are spinning at different rates. That means inaccurate, false readings, resulting in you not knowing how fast you’re actually driving. In turn, if you underestimate your speed and have mismatched tyres, your stopping distances may be compromised.

2. Less accurate handling

Fitting mismatched car tyres can adversely affect your steering, acceleration, and the all-round general handling characteristics of your car. Uneven car tyres can lead to less grip, and that means less control. Your vehicle will feel sloppy, and you may struggle to achieve shorter stopping distances in most cases, let alone on wet, cold, or icy roads when you really need them.

3. Sluggish acceleration

Mismatched tyres can mean it takes your car noticeably longer to get up to speed (because, like with improper alignment, your wheels are sort of fighting each other). This is especially dangerous if you find yourself suddenly needing a burst of speed to evade danger, such as a potential collision.

4. Unreliable traction

If one of your car tyres is wider than all the others, it’ll ultimately cause instability – especially at high speeds, and particularly in wet or icy driving conditions. This is because a wider tyre has more surface area in contact with the road, so will tend to grip the road a lot more. Now, while “more grip” is usually a good thing, more grip on one corner means that your car’s likely to want to pull off to a side.

5. You could damage other components

Fitting mismatched tyres, over the long term, risks damaging your car’s wheel bearings and even damaging the clutch, alongside creating other problems in your steering systems. The cost of these repairs usually far outweighs the money saved by fitting a non-matched tyre.

Aren’t some vehicles fitted with different front and rear tyres?

While it’s true that some cars do have different tyres fitted on their axles, these are typically done deliberately at the vehicle manufacturer’s factory, in partnership with tyre makers. The cars in question are often rear-wheel-drive BMWs and Mercedes-Benz, which roll off the production line fitted with wider tyres on the rear wheels.

It should be noted that this doesn’t equate to a mismatch, since the same tyres are fitted on each axle. The vehicle manufacturers essentially make an intentional decision to increase the traction generated on the rear driving wheels, so as to enhance the car’s driving dynamics. These cars – as well as the ‘OE’ (Original Equipment) tyres selected – have been designed and built to accommodate different tyres. Find out more about replacing tyres in axle pairs, and why it’s important.

Are there any circumstances when I can change with my tyre size?

There are. As long as you match the exact same car tyre type across the axles you can employ those with a higher speed rating. You might consider doing this if, for instance, you intend to drive your car on a racetrack. 

You can also change your tyre size if you ever need to transport something heavy or if you’re pulling a trailer of some sort. You can fit tyres with a higher load profile, or those that are marked XL or RF – meaning ‘Extra Load’ or 'Reinforced'. A word of caution though; if you’re intending to make changes like these, it’s a good idea to check with your vehicle manufacturer, or with a car tyre expert at Kwik Fit.

Do you know how to read your tyre size?

It’s worth familiarising yourself with the numbers on your tyre sidewalls. Remember, they should all read the same. If you do so, you’ll always be sure to have the right tyres fitted, and if you’re checking for the first time you may even find there’s a mismatch.

For a quick guide to understand the numbers and letters on a tyre’s sidewall visit our tyre markings page.

If you’re unsure about tyre sizes, talk to Kwik Fit

If you’re unsure which tyres are right for your vehicle, get in touch with your local Kwik Fit centre. Our car tyre technicians can provide you with expert advice, answer your questions about tyre safety and much, much more. You can even book a free tyre check!