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What does the speed rating mean?
The speed rating is the manufacturer's designation for the speed capacity of a tire. Beyond the stated speed capacity, the tire may make the vehicle harder to control, including turning and stopping properly.
Note that speed ratings are also measured under optimal conditions. The tire manufacturer assumes you are driving on the dry, flat pavement with properly inflated tires and good working brakes and suspension.
What is a typical speed rating for the average vehicle's tire?
Most passenger tires are rated for “S” or “T” which equates to 112 and 118 miles per hour. Light trucks often have lower speed ratings, with N, P, Q, or R, starting at 87, 93, 99, and 103 miles per hour.
Is the speed capacity ever reduced?
Especially in the world of trucks and SUVs, the number certainly can be reduced by the payload within the truck. It's not easy or really even possible to know the exact capacity of your tires while carrying certain amounts of weight. The best suggestion is to slow down to what feels like a safe, manageable speed that you would be able to stop in short order from.
The speed capacity can also be reduced if you are driving on a repaired punctured tire. A punctured tire means that the exterior rubber is compromised and might not be able to handle the same speeds as before.
What happens if I exceed the speed rating?
Driving above the speed rating can have serious effects on your ability to control the vehicle, whether just making a turn, or more importantly, stopping. Driving above the speed rating for an extended period, especially while traveling with a load, can cause damage and possible destruction of the tire.
Thankfully, the speed rating is not a specific limit set by manufacturers above which tires have an instant problem. Your tire might be able to handle traveling above it's set speed rating for a little while, but we wouldn't push it.
Do high performance tires have higher speed ratings?
They certainly tend to. People who own a more powerful sports car can buy tires that offer a speed rating up to “W” or “Z.” Here is where things can also get confusing. “W” means up to 168 miles per hour. “Z” can mean 149 miles per hour or more – Z is really the tire manufacturers way of having you ask them what the speed rating on a tire really is, as categories “V” and up cover the same speeds.
Can I mix speed ratings on tires?
No, you should not mix speed ratings on tires. Doing so can make one tire drive differently from another and make your vehicle potentially difficult, if not dangerous to drive. The speed rating reflects how the tire reacts to movements at certain speed, and you don't want tires of different abilities.
It is, however, possible to mix tire sizes as long as the tires have the same speed ratings. We suggest looking at your vehicle's owner manual before doing this.
Where do I find the speed rating?
The speed rating is at the end of your tire's code, which includes the radius, sidewall size, rim diameter, and load rating. For example, a tire can be an P225/60/ R16 / 82 S with a speed rating of S – as it's at the very end.
How is the speed rating tested?
Speed ratings are machine tested in ideal circumstances by machines. A machine spins the tire a manufacturer wishes to receive a speed rating for at high speed, then at various speeds until it damages the tire. The tire is inspected for damage to see how fast the tire was going when it received damage.
Why letters and not numbers?
One reason why the ratings are listed in letters instead of numbers is because of space. Imagine a sidewall with a couple more numbers packed in!
Another possible reason is to give you a reason to look up the number. If manufacturers printed that their tire is capable of going 112 miles per hour on the tire, the driver might not take the moment to look at their tire and gauge what the tire is capable of.
How fast can the average modern car go?
Let's think about this: Your tires are capable of driving your car at 112 to 120 miles per hour in ideal conditions. Should you drive that fast? Most modern cars have a speed ceiling of about 120 miles per hour before the engine can't push any harder and the vehicle becomes very difficult to control. In reality, most people won't come close to exceeding either their engine capacity or their speed rating.
The concern lies more on sports cars and tires that may be less capable than the engine itself, in addition to trucks that plan to carry a significant load on low speed rating tires. Truck drivers should be considering their overall capacity for weight along with what their tires are rated for.
Should I worry about the speed rating on my tires?
To be honest, speed ratings are a fun fact to look up, but they apply to very few situations. A vehicle driving alone on the highway might have enough room to reach the speed rating listed on the tire. The actual speed already violates most, if not all, speed laws in the United States, so getting a huge fine and an increase insurance rates are another chance you take.
One of the biggest factors in speed rating is not whether or not the tire will survive, so much as the after effects. A car traveling 110 miles per hour has a significantly longer stopping distance than one going the speed limit, and has a higher potential to do something unexpected while turning. The speeds as listed on a speed rating are more likely in a high speed chase than in normal driving.
Do higher speed rating tires cost more?
A higher speed rating typically comes on a more performance oriented tire. These tires also have different kinds of treads built in. The difference is often in stickness and ride comfort – a high speed tire will be softer and stickier – allowing it to form to the pavement and not leave the road while moving fast.
Tires like those suggested typically cost significantly more than normal all season passenger tires and often wear out faster too because they are designed to handle heat and speed.
Sports car drivers will also often have different sets of tires for different times of the year, in addition to potential track tires that are mode exclusively for dry, high speed cornering, and acceleration. These tires are usually at the end of the alphabet for the speed rating.
About The Author
I've spent many years selling cars, working with auto detailers, mechanics, dealership service teams, quoting and researching car insurance, modding my own cars, and much more.Read More About Charles Redding