In a dimension like 225/45 R17 94WThe 94W designation is just as important as the width or diameter. It defines the load capacity and speed rating of the tyre.
The load index
The load index is a number in a standardized table that indicates the maximum load a tyre can support under the intended conditions. It is not a directly readable number in kilograms.
- 91 corresponds to 615 kg per tyre.
- 94 corresponds to 670 kg per tyre.
- 98 corresponds to 750 kg per tyre.
The total capacity is not simply chosen by multiplying this value by four. The weight distribution per axle, the pressure, the vehicle specifications and the conditions of use must be respected.
The speed index
The speed rating is a letter corresponding to a standardized maximum speed category:
- H : 210 km/h
- V : 240 km/h
- W : 270 km/h
- Y : 300 km/h
This value describes a technical capability tested under defined conditions. It never changes speed limits or safety rules.
Can we choose a higher index?
A load or speed rating higher than the minimum approved value is generally technically feasible when all other characteristics are compatible. However, it may affect comfort, weight, rigidity, or price. The manufacturer's specifications always take precedence.
Why an insufficient index is dangerous
An undersized tyre can overheat and deform more easily. The risk increases with load, speed, heat, long journeys, and incorrect tyre pressure. The problem may not be visible when the vehicle is stationary.
What is the purpose of the XL marking?
XL stands for "Extra Load." It identifies a reinforced tyre capable of supporting a higher load at a given pressure. The XL marking does not replace checking the exact load index and pressure recommended by the manufacturer.
The verification method
- Note the dimensions and specifications indicated by the manufacturer.
- Check the full dimensions of the item ordered.
- Consider use with heavy loads, trailers or many passengers.
- Never replace a clue with an assumption based solely on the vehicle model.
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