Together, the load index and speed rating form the service description. When tire speed ratings were first developed in Europe in the s, there were only three ratings: S, H and V. As tire technology developed and new speed classes were introduced, the ratings table expanded to include the full alphabet. But the letter H kept its original speed rating of mph, so it sits later in the chart. Z-rated tires will sometimes have the letters ZR embedded with the tire size information instead of in the service description.
Tires with higher speed ratings offer handling benefits that thrill some drivers, but there are tradeoffs. The system is based on a lettered code and each letter corresponds to a speed. The tyre speed rating is clearly displayed on the sidewall of each tyre and indicates the fastest speed that a driver should not exceed when their vehicle is fitted with those specific tyres.
The speed rating numbering system run from A1 to A8 in sequence, whilst the letters run from B to Y. As seen in the tyre speed rating chart below, V corresponds to mph. Therefore, tyres with this speed rating should not be driven over mph. Most vehicles fit into the speed rating of S or T for or miles per hour limits or kilometres per hour. The speed ratings for wide diameter tyres are often higher as they are usually fitted to higher-performance vehicles.
Each letter corresponds to a specific speed. In general, that speed goes up as the rating advances alphabetically. This was for tires whose maximum sustained speed was mph kph or more. They begin with a maximum speed of mph kph and increase from there. Nowadays, it means mph but no higher. When it does, it represents either a maximum speed of more than mph kph or mph kph. This is to prevent a potential oversteer scenario. Bear in mind that all tyres must be appropriate for the vehicle and you should drive no faster than your lowest rated tyres.
We would always recommend that the same size and type of tyre, with the same speed ratings, are fitted on all tyres. Tyre speed ratings.
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