Tyre Terminology Explained – Part 1
Looking for replacement tyres, or buying tyres online can be a minefield of confusion terminology and technical terms. It can all be a bit overwhelming, and you may feel too embarrassed to ask for an explanation in person at a garage. Fear not! Here are some of the most common technical terms, explained in a language anyone can understand:
Aspect Ratio – This means the difference between the tyre’s width and height of the sidewall (which is, as you might expect, the side of the tyre). The higher the ratio, the ‘taller’ the tyre is. A higher aspect ratio makes for a smoother ride and provides better grip on snow. A lower aspect ratio usually comes with ‘low profile’ tyres which might be used on high-performance cars – they have excellent handling and grip, but may also leave you with a harsher ride.
Contact Patch – The contact patch is the small portion of your tyre’s tread that actually makes contact with the road at any one moment. Sport tyres are much wider, so have a bigger contact patch, which gives them extra grip when cornering and faster acceleration.
Treadwear indicators – Also known as ‘wear bars’, these are the little bands or ‘bridges’ that go between the tread on your tyre. When your tread wears down, they begin to become visible, giving you a visual indication that your tyres need to be replaced.
Speed Rating – If you look on the side of your tyre, you’ll see a whole load of symbols and digits. The speed rating is the letter that usually comes towards the end of this data and refers to the maximum speed your tyre is capable of. Most current models of family car have a speed rating of S or T (allowing for top speeds of between 112 and 118mph). High performance cars may have higher ratings, such as V or ZR (allowing for speeds up to and above 149mph).
Maximum Cold Inflation Load Limit – Bit of a mouthful, but all this means is the maximum load that the tyres are capable of carrying, and the maximum air pressure required to support it. This information (your recommended cold inflation load limit) should be in your vehicle’s handbook. Overloading your vehicle and/or under/over-inflating tyres can be dangerous and affect your car’s handling. The ‘cold’ aspect of the terminology refers to the fact that you should always check your tyre pressure when your tyres are cold. Checking them too soon after driving, when they are warm, means that you will get a false reading as heat will increase the pressure inside the tyre.
Look out for Tyre Terminology Explained – Part 2 tomorrow, which includes easy to understand explanations of load index, treadwear ratings and radial tyres…