Modern passenger tyres now have a tyre speed rating embedded on them—it’s the last letter in the character sequence of the tyre size code on the sidewall. The tyre speed rating refers to the maximum speed a tyre can handle for a certain period of time without risk of failure. This does not mean, however, that the vehicle may be driven at the fastest speed the tyre can handle, especially during adverse weather conditions.
How Speed Ratings are Determined
Speed ratings are determined under controlled testing conditions in the laboratory, through simulation of speeds and loads. Before a tyre receives a particular rating, it must first exhibit that it’s capable of handling a particular speed.
However, even under a controlled testing facility, the laboratory cannot create every imaginable condition. Factors such as inflation, wear, vehicle condition, driving conditions and the maintained speed duration can affect the actual tyre speed capability and thusm, lessen your tyre’s speed rating.
Speed ratings are also aren’t applicable to damaged, overloaded, altered, repaired or under-inflated tyres. Therefore, your tyre’s speed rating is simply an indicator of its capability under controlled conditions. These conditions include the tyres being fully inflated, fitted on vehicles on proper running conditions, and tested under good weather conditions.
Finding Your Tyre Speed Rating
If you want to know your vehicle manufacturer’s recommended tyre speed rating, you can always look it up in the car owner’s manual. You can also check it out in your vehicle. There are three places where you can find the speed rating: the driver’s side door jamb, glove box door, and the gas tank hatch.
How Speed Rating Affects Your Vehicle’s Handling and Safety
Gets rid of heat build-up. Aside from poor driving habits and extreme road conditions, heat is your tyre’s worst enemy. Tyres with low speed ratings don’t respond well to pressure, which leads to heat build-up. And if you combine heat build-up with high temperatures, then expect to notice a real difference in your tyre’s performance and durability. You could also risk tyre degradation, reduced traction, and even sudden blowouts.
On the other hand, tyres that have higher ratings are well equipped to get rid of heat, and avoid its many consequences. This is due to their higher quality construction and ply.
Lower-rated tyres don’t respond well under hard braking. Speed rating can also affect your braking. Tyres with a lower speed rating will squirm under hard braking. This means it might take longer to stop during emergency situations.
Ratings indicate your tyre’s ability to take sharp turns safely. Contrary to what others believe, it’s the quality of your tyre’s construction—not the size—that’s going to help you take tight curves and sharp turns safely. And under force, lower-rated tyres are known to experience a change in shape and contact patch, which can reduce your traction.
High- and low-rated tyres have a different steering response. High-rated tyres generally respond quickly and accurately, so you won’t have to turn your wheels as much. And a fast steering response is priceless, especially when you have to dodge a dog or any debris on the freeway.
It’s important to bear in mind that tyre speed ratings aren’t just about speed, but they also make a difference in your ride comfort, grip, and stopping power.