The speed rating tells you the speed the tire can safely maintain over time. A higher speed rating usually means you will have better control and handling at higher speeds — and that the tire can take the extra heat. Generally, tires with higher speed ratings also handle better at slower speeds..
Spare Tire Life & Safety
When you have to use your spare, it’s urgent to know the limits of you’re a spare tire. Spares are not designed to drive at the same speed as regular tires; never let your speed exceed 50 miles an hour when you’ve got a spare on your car. Most spare tire mileage is around 50 miles.