Speed Ratings and Changing Tire Sizes

Speed Ratings and Changing Tire Sizes

Changing tire sizes can affect the speed rating and speedometer accuracy.

If you look at the sidewall of Continental TrueContact Tour, you’ll see it has a “T” speed rating. That means the maximum speed capability or speed limit at which the tire was designed to perform is 118 mph. So, for optimal performance, your customer shouldn’t go above that speed with this tire.

But say your customer wants to upsize or change tire sizes, how does that affect the speed rating? In this Tire Review Continental Tire Garage Studio video, we’ll discuss that and other considerations for a tire’s speed rating.

When vehicles come off the assembly line, their speedometer was calibrated by the factory according to the exact size of the tires intended for the vehicle. So, changing tire sizes can not only change the speed rating but also the accuracy of the speedometer.

Up-sizing, or installing a taller tire, can lead to a speedometer reading that is slower than your actual speed. That’s because a taller tire will have a larger overall circumference, causing it to need to travel more distance per revolution than the OE tire.

If you’re installing a shorter tire, or down-sizing, the speedometer could indicate a faster speed than the car is actually driving. A smaller tire has a smaller circumference, causing the tire to travel less distance per rotation than the OE tire.

Now, if you’re plus sizing, replacing the OE tire size with a different size–but one with the same overall height and diameter– should not interfere with the speedometer. But it does mean you should replace your OE rims with a larger or smaller size to maintain the same tire height.

If your customer upsizes or downsizes their tire size, it could be necessary to recalibrate the speedometer. This ensures that your driver knows the speed that they are traveling, and that the vehicle is reading the speed correctly.

Some dealers and tire manufacturers have a tire size and speedometer calculator specifically for instances like these.

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