For S-speed-rated tires, it's 112 mph; for T, 118 mph. Speed ratings for other tires include Q, 99 mph; H, 130 mph; and V , 149 mph. Some tires have speed ratings of W, 168 mph and Y, 186 mph.

Those letters and numbers on your tires are not just gibberish. Understanding this information is key to road safety. Let's ...