If you’re in the market for a new set of tires or in the unfortunate position of needing a single tire replacement, an important thing to consider is “tire speed rating.”
When automobile engineers design a vehicle, the type of tire they choose plays a major part in the design of the suspension and braking systems. Which means that the tire you buy has a direct impact on your vehicle’s ability to keep the rubber on the road and perform the way it was designed to perform.
What does “speed rating” on tires mean?
Tire speed rating is a designation indicating the tire’s speed capability and expected performance. Understanding what it means — beyond the cost differences — and how to find it is critical to making sure you outfit your car or truck with the right tire.
The simplest way to define speed rating is the fastest speed a tire can handle before it no longer performs as designed. It should not be considered the maximum speed that you can safely drive — especially in adverse weather or road conditions. A common misconception is that, if you’re not going to drive as fast as the maximum speed designated by your speed rating, it’s okay to downgrade to a lower rating. The attraction of purchasing a less expensive, longer-lasting tire diminishes when you understand that this decision comes with a risk.
Safety and performance
So, what is it about your tire that lets your vehicle safely brake or turn in emergency situations? It’s the sidewall design, the tread pattern and the stability of your tire’s rubber compound. These elements combine to make up your tire’s speed rating or, another way to think about it, your tire’s performance rating. Not surprisingly, the higher a tire’s speed rating, the higher its performance, safety and handling characteristics.
How to find your tire speed rating
You can find the recommended tire specifications in your vehicle owner’s manual. If you don’t have access to the manual, you may find a sticker with the information on the driver’s side door jamb, the gas tank hatch or the glove box door.
When shopping for new tires, you can refer to the sidewall of the tire itself to find all of the information you need to know, including the speed rating. The speed rating is the last character in the sequence of the tire’s size code.
For example, if you have a tire with the size code “P205/55R19 92T,” T is the speed rating.
How to read the ratings
European manufacturers started using speed ratings in the 1960s to ensure their increasingly speedy cars would be outfitted with appropriately safe tires. These early speed ratings are the foundation for the tire speed system that we use today.
The rating system is a series of letters and corresponding maximum speeds.
A common starting place for passenger car tires is an “S” rating, meaning that maximum speed capability of the tire is 112mph. The next rating is “T” and then “U” and so on with maximum speeds increasing with each letter. All ratings cover speeds that are well above legal limits.
Tire Speed Rating Chart
There are some quirks to this rating system. If you noticed H is out of place and not in alphabetical order ... that’s not a typo. It’s a holdover from the early European system, which the tire experts at the time chose not to change.
You may also notice the maximum speeds of W, Y and (Y) are faster than that of Z. When Z was introduced, it was thought to be the highest speed rating tires would require. As vehicles kept getting faster, W, Y and (Y) were introduced to provide a better indicator of a tire's capability at speeds higher than 149 mph.
A safety note: Ratings shouldn’t be a performance expectation of any tire that has been damaged or has worn down to 2/32". So, if you have a tire repaired, the ratings may not apply.
Installation of mismatched speed-rated tires on your car is not recommended. But if you find yourself with no other option, it’s important to know that maneuvering corners and general handling of the vehicle can be compromised by mixing the tire speed ratings assigned to your vehicle. For the best performance and safety, the manufacturer’s recommended size and speed rating should be selected for all tires.
The only time it’s okay to downgrade your tire speed rating is with winter tires, where a Q rating is acceptable because you’re likely to be driving at a slower speed and in colder temperatures.
Be comfortable with your speed rating
Along with speed, wear and cornering ability, the proper speed-rated tire for your vehicle contributes to increased ride comfort. Automakers spend millions testing the performance of a car — which includes driving comfort — with the specific tire configuration they recommend. So, to get the best safety and performance from your tires, make sure that you have tires with an approved speed rating for your car.
Vehicles do not always come with a spare tire, but you might not notice this until it’s too late (when you are on the side of the road with a flat). It’s important to always have a back-up plan. Tireamerica.com has a guide created to help you understand the best options for you.