Tire Speed Rating and Why It Matters
One of the most important aspects of any tire is its speed rating. The wrong tires with a less-than-adequate speed rating for your vehicle can cause safety issues, including tire failure and a loss in fuel efficiency. Let’s take a look at speed ratings, where to find the right one for your car or truck, and why it should always match the needs of your vehicle.
What Is the Speed Rating on a Tire?
The tire speed rating is the maximum speed tires can safely carry a load (the original weight of your vehicle plus whatever’s in it) for a sustained amount of time in ideal conditions. The speed rating sits alongside the load index on the side of every tire. Also called the performance rating, the letter (or letter/number combination) rates the tire’s performance in dissipating heat, cornering, braking, and steering. The letter in a speed rating represents a maximum speed based on a standard chart (seen below).
Tire Speed Rating Chart
|SPEED SYMBOL||SPEED (mph)||SPEED SYMBOL||SPEED (mph)||SPEED SYMBOL||SPEED (mph)|
|B||31||P||93||*For tires having a maximum speed capability above 149 mph, a ZR may appear in the size designation... above 186 mph, a ZR must appear in the size designation, including a Y speed symbol in brackets.|
|SPEED SYMBOL||SPEED (mph)|
*For tires having a maximum speed capability above 149 mph, a ZR may appear in the size designation... above 186 mph, a ZR must appear in the size designation, including a Y speed symbol in brackets.
Speed Ratings 101
Generally, the higher in the alphabet a tire is rated, the better it will manage heat and faster speeds.
Your actual speed capacity may be less than a tire’s rating. The rating indicates a new tire’s performance in tightly controlled lab settings, not the open road. Tire condition, inflation level, extra cargo, road surfaces and weather affect a tire’s maximum safe speed.
If you have tires with different speed ratings, the limit of the lowest-rated tire is the fastest you can safely drive and stay within your tires’ capability.
The most common ratings are S and T (sedans, minivans, light trucks); H (some passenger cars, sports cars, coupes, some light trucks); N, P, Q and R (light trucks); and V, W and Y (high-performance and some electric vehicles). Most winter tires have Q, S or T speed ratings.
Tire speed rating is not like a speed limit posted on highway signs. It’s based on lab simulations and doesn’t account for real-life factors that determine true tire capabilities, such as proper tire inflation, wheel and tire balance, vehicle alignment, tire tread, weather, and other conditions.
Don’t use the rating as a guideline for the top speed you can drive. If you’re carrying a heavy load or your tire is low on air, your tire’s speed capacity will be reduced. For safe driving, keep your speed at the posted speed limit — or below, when road conditions or the weather aren’t ideal. After a tire puncture has been repaired, keep in mind that some manufacturers suggest a tire’s speed rating may be reduced.
Where Do I Find My Tire’s Speed Rating?
From left to right on the sidewall of your tire, you’ll likely find the tire class (indicated with a letter), the section width (number), aspect ratio (number), the tire construction (letter), the tire’s load index (a two to three-digit number that corresponds to the weight each tire can support), followed by the speed rating. You can also find the speed rating in your vehicle owner’s manual, on a sticker in the driver’s side door, or stop by Les Schwab and we’ll look it up.
How Are Speed Ratings Determined?
Tire manufacturers determine a tire’s capacity for heat and speed using a testing machine. Testing is done to meet ECE (Economic Commission for Europe) standards, with a scale based on kilometers per hour (km/h). A more rigorous test is sometimes done to meet SAE (Society of Automotive Engineers) standards.
For the ECE test, the tire is properly inflated and mounted on a wheel attached to a testing machine in a room that’s heated to 77º F. The tire is then pressed against a metal drum with enough pressure to simulate a realistic load.
Starting at a speed of 40 km/h lower than the proposed rating level, the tire is spun for 10-minute increments at higher and higher speeds until it reaches the target speed. The tire spins for 10 minutes at the target speed. It’s then removed from the machine and inspected for any failures, like separation of tread components. If it’s intact, it passes the speed rating.
Sometimes an SUS (step-up speed) test will be added after the tire performs at the target speed rating. Speed is increased until the tire fails. If the tire is being tested at the SAE standard, it’s required to run for an hour at target speed in a room heated to 100 degrees.
Does Tire Speed Rating Affect Your Driving and Tread Life?
Tires with higher speed ratings offer handling benefits, but there are tradeoffs. Since they’re usually made with softer rubber compounds and stiffer construction, they offer better cornering, stopping power and steering response. However, there can be less ride comfort, lower performance in cold conditions, and shorter tread life.
What Tire Speed Rating Do You Need?
Even in states where rural speed limits are 75 mph, most drivers will stay well below the speed limitations of H-rated tires. Commuters and family car drivers will likely be quite satisfied with S or T tires. Are you a “spirited” driver with a high-performance vehicle? You may be happier with V, W or Y tires. Light truck drivers should look for symbols N, P, Q, R, S, T or H.
If you’re replacing tires and think you may want a lower- or higher-speed-rated tire, it’s best not to mix and match. When mounting differently rated tires, techs prefer to put the lower-speed-rated tires on the front to prevent oversteering. This can conflict with the best practice of putting the tires with the most tread on the rear, which is important for wet traction.
Les Schwab Is Your Tire Experts
The pros at your local Les Schwab can show you all of the options you need for work, weekends, or your daily commute. Add in our Best Tire Value Promise with unlimited flat repairs and free tire replacement and rotations, and you’ve found a partner who cares about service and your safety on the road.
Important Notice: The information provided above is derived from sources deemed reasonably reliable. The operation of your vehicle, or the replacement of your vehicle’s equipment, may be different than for a typical vehicle. Please consult your owner’s manual for specific warnings, notices, and other advice relative to the subjects addressed.