We often forget that tires are the most important part of our vehicle. We tend to forget because, well, once we’ve bought our tires we don’t really need to think about them for a few years. That said, some drivers make the mistake of thinking their tires can handle anything, when in reality they can’t.
Tires have thresholds and limits which are easy to find and tell you right away what you can and cannot do with your vehicle when those specific tires are on.
Every tire fits within a specific speed rating. There 10 speed ratings in total and in essence what that does is tell you the maximum speed you can reach with a specific tire. If you should go over that speed, you run the risk of having your tire fail which, in the event you are going so fast as to damage your tire, would be catastrophic.
Moreover, vehicles are designed by their manufacturers to reach certain handling and braking performance levels. The automakers then base their tire choice on those performance levels. When you replace your tires, it’s important to go with a tire that has the same speed rating if you wish not only to preserve your vehicle’s driving dynamics, but also your own safety.
It’s very easy to find your tire’s speed rating. You just have to look at it. You will find a marking that looks something like this: P225/65R15 95H.
The first letter represents the tire type. In most cases, it will be a P which means this tire is made for passenger vehicles and complies with all regulations. The set of numbers that follow represents the tire width, in this case 225 millimeters. The second number is the aspect ratio which compares the height of the tire to its width. So for example, 65 here means that the height of the tire is 65 % of the size of the width. The letter that follows refers to how the tire is constructed. This will generally be the letter R because the layers of the tire run radially across. Then we have the wheel size, in this case 15 inches.
Then finally we have the last two numbers and the letter. The first numbers represent the maximum load a tire can bear when fully inflated while the final letter is the tire speed rating. Here is a chart explaining speed ratings:
Q : 160 km/h
R : 170 km/h
S : 180 km/h
T : 190 km/h
U : 200 km/h
H : 210 km/h
V : 240 km/h
W : 270 km/h
Y : 300 km/h
Z : More than 240 km/h
Thank you to Lexus of Kingston for their help with this article.