The speed rating tells you the speed capability of your tire. Summer tires will typically have higher speed ratings than winter or all-season tires, as they are designed to go faster. The higher the speed rating, the more robust the tire construction. As long as you get at least an N-rated tire, you’re safe to drive at the fastest speed limits in the US. Most non-winter tires are rated for at least 100 mph, a capability you would only need if you take your to the track. But if you do track your car, make sure you get good performance tires that can handle the significantly higher speeds your car can achieve there.