Advanced Tyre Search

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Why can't I put just any tyres on my car?

It may seem obvious, but your wheels and tyres are vital components of your vehicle - after all, your tyres are the only part of your car touching the road (at least, that should be the case!) - but many people don't give a second thought to the tyres they choose. Knowing and fitting the right tyres for your car will give you the best performance out of your car, and keep you safer on the road.

So why can't you fit just any tyre onto your car? Well, your car is designed to use a specific rolling diameter and circumference. If you change this by more than 3% you are likely to compromise your gearing, your speedometer won't reflect your true speed, and on full steering lock it may be that your tyre will touch your wheel arch or suspension. As a rule of thumb, it is best to stay within a 1% tolerance of your original tyre size, though going to 3% tolerance is acceptable. Fitting tyres beyond a 3% tolerance is not advised, as it will impact your tyre's performance and safety.

You also need to make sure your rim and tyre width are compatible. If they're not, it can mean that your tread won't make proper contact with the road (resulting in a loss of traction), your sidewalls can lean in or out and the the bead of the tyre won't seal correctly, which can result in sudden air pressure loss.

You also need to ensure you fit tyres with the correct speed and load index for your vehicle. If these are insufficient either from a speed or gross mass perspective, you run an increased risk of a blowout or sudden pressure loss.

If you're planning to fit a tyre with a larger or smaller rolling circumference, you can use our handy guide above to see what tyre sizes will safely fit within the maximum 3% tolerance for your vehicle to stay safe and performant.

Want to put bigger rims on your car?

Many people want to increase the size of their rim to there car. This is doable, but does come with a number of trade-offs:

• The larger the wheel, the higher the rotational mass is, so you will lose fuel efficiency.
• Thinner sidewalls also ride harsher as the tyre won't flex as much. Bumps in the road will be felt more with less vertical cushoining.
• Wheels are heavier than tyres, so as wheel size goes up, so does weight, which can negatively impact fuel economy and acceleration, whilst also making the steering heavier.
• You need to ensure your adjusted tyres are within the vehicle's engine management system specs - some vehicles can pick up if the differential exceeds its expected tolerances and shut down the engine.

Moving to lower profile tyres can, however, also improve performance - with the shorter sidewall flex, the tyre will maintain better grip, and a wider tyre will also improve lateral stability.

Metric vs Imperial Tyre Sizes

Tyre measurements can get complicated when trying to compare tyres using imperial (also known as standard) or metric measurements. So what is the main difference between, for example, a 315/70R17 (metric) vs a 35×12.5R17 (imperial) tyre?

Metric (eg. 315/70R17):

• 315 = 315mm in width across the tread of the tyre (also known as section width).
• /70 = Aspect ratio. This is the height of the tyre's sidewall expressed as a percentage of the tyre's section width.
• R = Radial construction - This refers to the construction of the tyre. Radial tyres have plies of reinforcing tyre cord extending from bead to bead at a 90 degree angle to the centreline of the tyre.
• 17 = Rim diameter in inches.

Imperial (eg. 35x12.5R17):

• 35 = The outside diameter of the tyre in inches.
• 12.5 = The section width of the tyre in inches.
• R = Radial construction.
• 17 = Rim diameter in inches.