What tyre size do I need for my car? UK guide

At a glance:

In most cases, fit the size on the sticker inside your driver's door or fuel flap, in your handbook, or on your current tyres' sidewall. A different size is acceptable when:

• The rolling circumference stays within roughly ±3% of the original.
• The tyre doesn't foul the wheel arch at full lock or full suspension travel.
• The load index and speed rating match — or exceed — the manufacturer's specification.
• Both tyres on an axle are the same size, and you've told your insurer.

Where to find your tyre size: registration, door sticker, handbook or sidewall

The quickest way to find your correct size is to enter your registration number into a tyre lookup tool, or check your vehicle handbook, which often lists more than one approved option. You can also read the code straight from your current sidewall, provided it's the original size or a previously approved variant — just make sure the wheel rim diameter matches.

Prefer not to dig through paperwork? Visit your local Point S centre and our technicians will confirm your exact size and fit it on the spot.

Why your car may be approved for more than one tyre size

• Your vehicle is often approved for multiple tyre sizes depending on the trim and wheel specification. For example, a car might use 205/55 R16 tyres for comfort or 225/45 R17 for a sportier feel; both maintain a similar rolling circumference to keep the speedometer accurate.
• Furthermore, manufacturers frequently approve smaller rim diameters for winter tyres. Fitting a narrower tyre on a smaller wheel can improve traction in snow and reduce replacement costs.
• Finally, high-performance rear-wheel-drive models often require a "staggered" setup, where the rear tyres are wider than the front. While sizes differ between the front and rear, UK law mandates that tyres across the same axle must be identical to ensure stability, optimal performance, and a successful MOT result.

Can I fit a different tyre size? UK rules for a legal alternative

The ±3% rolling circumference rule

The core principle: a replacement tyre's rolling circumference should stay within roughly ±3% of the original — measurable with a rolling-circumference calculator. Any larger change should be declared to your insurer, and must comply with ETRTO technical standards. Fit the wrong circumference and your speedometer will read inaccurately.

• When considering an alternative tyre size, you must adhere to strict legal frameworks to ensure your vehicle remains roadworthy. Under  UNECE Regulation R39 , the law dictates that a speedometer must never underestimate the speed of the vehicle. Fitting a tyre with a significantly larger circumference can cause the speedometer to under-read, potentially rendering the vehicle unlawful and leading to unintentional speeding.
• The Road Vehicles (Construction and Use) Regulations 1986 mandate that every tyre fitted must be of an appropriate size and type suitable for the vehicle's use. Compliance is strictly monitored during the annual MOT test; for instance, having two different tyre sizes on the same axle is classified as a major fault, resulting in an immediate fail.
• Finally, it is a requirement of your motor policy to disclose any deviation from the manufacturer's original specification. Any change to the tyre size is considered a vehicle modification and must be reported to your insurer. 

Check your tyre size using a tyre size calculator

Run the original and proposed sizes through a tyre size or circumference calculator to check the deviation instantly. Before changing size, also confirm that the wheel rim diameter matches and the tyre clears the wheel arch at full lock and suspension travel. Don't forget to double-check your tyre pressure too — it should be adjusted whenever tyre dimensions change, for optimal performance and safety.

Find your nearest Point S garage to book your tyre size and alignment check. 

Point S tip: Our technicians cross-check three sources — the sidewall code, the door-jamb sticker, and the vehicle handbook. If all three align, you're on solid ground.

Know your size? Get the right tyres fitted

Finding the correct replacement tyres is essential for maintaining vehicle safety, legal compliance, and optimal performance on UK roads. While alternative sizes are sometimes permissible within a ±3% rolling circumference tolerance, it is a legal and safety requirement that your tyre size, load index, and speed rating stick to manufacturers specs to ensure the speedometer remains accurate and the vehicle stays roadworthy. If you are unsure, our expert technicians are ready to assist you at your nearest Point S centre. 

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Frequently asked questions

How do I know what size tyre I need for my car?

Check your registration via a lookup tool, or your current sidewall. As long as the load index, speed rating and rolling circumference stay within tolerance, you're within the rules.

What size are my tyres?

Look at the sidewall's alphanumeric code — e.g. 205/55 R16 91V, the most common size on UK roads, though it varies by model and trim. Need help to understand your tyre dimensions? Read our dedicated expert guide about how to read your tyre size.

Is it legal to fit a different tyre size from the manufacturer's spec?

Yes, it is legal to fit alternative tyre sizes in the UK provided they are fit for purpose. The new size must maintain a rolling circumference within ±3% of the original to keep the speedometer accurate, meet or exceed the required load index and speed rating, and be identical across the same axle. Always inform your insurer of any deviation from manufacturer specifications.

What happens if I fit the wrong tyre size?

Fitting the wrong tyre size can cause an inaccurate speedometer, longer braking distances, uneven wear, a roadside prohibition notice, an invalidated insurance claim or MOT failure. If you're unsure, your local Point S centre can confirm the right size and replacement tyres for how you drive. Beyond size, factors like low tread depth or structural damage also dictate what makes your tyres illegal.

Can I fit 235 tyres instead of 225?

Often yes, provided the change stays within the ±3% tolerance explained above and the load index and speed rating equal or exceed the original spec. A wider tyre can improve grip, but get the match wrong and you risk uneven wear and weaker wet-weather performance. Ask a professional before buying replacement tyres if you're unsure.

Does the V5C show my tyre size?

No, the UK V5C logbook does not explicitly list tyre sizes. It contains technical details like engine capacity and VIN, but for tyre specifications, you must check your vehicle handbook, the driver’s door sill sticker, or the current tyre sidewalls. 

Why are my front and rear tyres different sizes?

This is likely a "staggered setup," common on rear-wheel-drive performance cars to improve traction and stability. While sizes may differ between axles to enhance power delivery, UK law requires tyres on the same axle to be identical. Always follow manufacturer specifications to ensure safety, speedometer accuracy, and MOT compliance.

Can I put bigger wheels and tyres on my car?

Yes, you can fit larger wheels and tyres as long as they don't protrude beyond the wheel arches or rub against the bodywork. The new setup must maintain a similar rolling circumference (typically within ±3%) to keep the speedometer accurate. You must also notify your insurer, as this is considered a vehicle modification.

Do all four tyres need to be the same size?

In the UK, all four tyres do not have to be identical, but those on the same axle must match in size and construction. While mixing brands is legal, it is recommended to use the same size, load index, and speed rating on all wheels for optimal stability and performance. Front and rear tyre sizes can differ only if specified by the car manufacturer.