The Ultimate Guide to Commercial Tyre Speed Ratings

Understanding the speed index isn’t just about how fast a vehicle can go; it’s about heat dissipation, load capacity, and protecting your bottom line. This guide breaks down everything you need to know about commercial tyre speed indexes with a focus on the Australian market.
 

What is a Commercial Tyre Speed Rating?

The speed rating (or speed index) is an alphabetical code that indicates the maximum safe speed a tyre can maintain when carrying its maximum load capacity. For commercial operators, this rating is a critical safety threshold. Exceeding it generates internal heat that can lead to catastrophic casing failure.

Michelin Commercial Tyres – Speed Index by Specialisation

Key Selection Guidelines

Selecting the right tyre requires more than just looking at the price tag. Keep these expert guidelines in mind.

● Location of Rating You can find the speed index on the tyre sidewall immediately following the load index. An example would be 154/150 L.

● The Replacement Rule Michelin recommends that replacement tyres must have a speed rating equal to or higher than the original equipment specified by the vehicle manufacturer.

● The Unique Point Some Michelin truck tyres feature a second load or speed index in brackets. This indicates the tyre can carry a higher load at a lower speed rating. For instance, a unique point rating might allow for more weight if you drop from a speed rating of L to G.

● Dual Marking in Agriculture Ag tyres often show two ratings such as 145A8 / 139D. This means they can carry more weight at 40 km/h but safely operate at 65 km/h if the load is reduced.

● Australian Legal Compliance Most highway going commercial vehicles in Australia require at least a G or J rating to stay compliant with state transport regulations and speed limits.

● Heat Dissipation Tyres rated A1 to G are built with thicker casings. These hold more heat. This means exceeding the speed limit can cause delamination where the tyre layers peel apart.

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