Breaking the “tire code”:
Understanding tire service description, load rating, and speed rating
If you look at the sidewall of a tire, you’ll see a whole slew of characters and numbers. This is basically a code that includes information about size, construction, and guidelines for use of the tire -- and we’re here to help you decipher it. In this article, we’ll look at just one small part of the code: the service description.
As an example, we’ll be using a 2012 Audi A3 TDI. This car’s “tire code” is 225/45R17 94H. You can usually find this information on a sticker on the driver’s side door jamb.
Tire service description
The service description is simply the speed rating and the load rating together. In our example, the service description is the last three characters: 225/45R17 94H
94 is the load rating and H is the speed rating. But what exactly does that mean…?
Tire load rating or load index
The load rating tells you how many pounds a tire can safely carry. In our example, the number 94 has been assigned to a load carrying capacity of 1477 pounds (per tire). So if your car was fully loaded up with, let’s say, bags and bags of dog food, you’d want to be sure the weight of the car plus the weight of the cargo didn’t exceed 5908 pounds (1477 x 4).
The GVWR (gross vehicle weight rating) for the Audi A3 is 4597 pounds. This includes the car, driver, passengers, dog, and dog food. Since the combined load rating (5908 pounds) for the four tires is greater than the 4597-pound GVWR, you’re good to go.
If you know the tire load rating for your vehicle, you can use our handy load index chart to check out the load carrying capacity of your tires.
|Load Index||Pounds (lbs)||Kilograms||Load Index||Pounds (lbs)||Kilograms|
When you shop for tires and give us your vehicle’s make/model/style information, we show you only the tires that have the proper load rating for that vehicle. If you choose a tire with a different load rating for some reason, that tire must meet or exceed the load rating for your vehicle.
Tire speed rating
Speed rating ensures that a vehicle’s tires match its top speed capability. Going back to our Audi, the “H” speed rating is equal to 130 miles per hour, meaning that under optimal conditions**, the tire can perform at speeds up to 130 mph. Now just a second, leadfoot … that doesn’t mean you should drive 130 mph. It means that the Audi A3 is capable of a top speed of 130 – but here in the U.S., it’s generally a good idea to observe the posted speed limits.
Just like with load rating, when you shop by vehicle we only show you tires with the correct speed rating for your car. If necessary, you can use a tire with a speed rating that is greater than the speed rating recommended for your car (for example, instead of using an H-rated tire on the Audi A3, you could use a V-rated tire (149 mph). If you must mix tires with different speed ratings, be sure to observe the lowest speed rating when driving.
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