Speed index truck tyres
The speed index was initially introduced to match the tyre's resistance with the (increasing) speed of the vehicle and is based on lab testing carried out by manufacturers. Each speed range has a specific letter (or letter/number combination for the lowest categories). During testing, tyres are pressed against a large, revolving metal drum and the speed of the drum is increased until the speed required for the tyre in question.
In this example (see image), the letter ‘M’ in the combination 154/150M indicates the maximum speed.
The indicated speed index only applies to tyres which are not:
- overloaded; or
- subject to insufficient pressure.
Manufacturers do not guarantee the original speed index for tyres which have been repaired. After all, they cannot judge the quality of the repair.
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Learn more about the load index