How to Read a Tyre Sidewall (Size, Load Rating and Speed Rating Explained)

Every tyre has its full specification printed right there on the sidewall. But unless you know what you're looking at, it reads like a string of random numbers and letters. Once you know the code it tells you everything you need to know about whether a tyre is actually right for your car.

Breaking down the size code

A typical size looks like this: 225/45R17 94V.

The first number, 225, is the tyre's width in millimetres. The second number, 45, is the aspect ratio (the height of the sidewall as a percentage of that width), so a lower number means a lower profile tyre with a shorter sidewall.

The "R" simply means radial construction, which is standard on virtually every passenger tyre made today. The 17 is the wheel diameter in inches that the tyre is designed to fit.

Load index: how much weight the tyre can carry

The number straight after the size — 94 in our example — is the load index, and it corresponds to a maximum weight the tyre can safely carry per tyre, taken from a standardised chart. It's not a figure you need to memorise, but it does matter: fitting a tyre with a lower load index than your car's original specification can mean the tyre is rated to carry less weight than the vehicle manufacturer says it needs to, which matters if you're fully loaded with passengers and luggage.

Speed rating: the letter that gets overlooked

The letter after the load index — V in this case — is the speed rating, and it indicates the maximum speed the tyre is designed to sustain under its full rated load. Speed ratings run from lower letters like Q and S through to higher ones like V, W and Y.

Fitting a tyre with a lower speed rating than the manufacturer specifies isn't just a performance downgrade, it can affect how the tyre handles heat build up, and in some cases, insurance implications if a tyre doesn't match the vehicle's original specification.

Why matching the original spec matters

It's tempting to save a bit of money by going with whatever's cheapest in a similar size, but the size, load index and speed rating together were chosen by the vehicle manufacturer for a reason .

They're matched to the car's weight, expected handling characteristics and braking behaviour. A mismatch on any one of the three can subtly change how the car handles, particularly under hard braking or in wet conditions.

If you're due for new tyres and want to make sure you're getting the right size, load and speed rating for your exact car, bring the car in to any of your local TYREPLUS HTR stores and we'll confirm the correct specification before you buy, rather than after.