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Tires June 17, 2020

A Guide to Tire Load Index & Speed Ratings

Ever been confused at what all those numbers and letters on the side of your tire mean? You’re not alone! We’re here to help clear up the confusion and help you might the right tire choice for your vehicle.

We’re taking an in-depth look at the tire service description, better known as the tire load index rating and speed rating.

(To learn what all the numbers on your sidewall mean, check out our blog on how to read tire sizes: What Do the Numbers on My Tires Mean? How to Read Tire Sizes)

A tire service description consists of a two or three-digit number followed by a letter. It is located immediately after the tire size description on a tire sidewall.

how to read a tire sidewall

Let’s look at the following tire size designation as an example: 225/40 R18 94Y. In this case, 94Y is the service description. The tire’s load index rating is 94, and the speed rating is Y.

Makes perfect sense, right? Don’t worry—there’s more to it. Keep reading to learn how to decode your tires’ load index rating and speed rating.

Tire Load Index Rating

The load index number is a shorthand way to describe the total load capacity of the tire. To find out how much weight a tire can carry, you’ll need a tire load index chart, like the one below.

Using our example tire size from above, let’s use the load index chart to calculate the total load-carrying capacity for the tires.

Based on the load index rating chart, 94 corresponds to a tire load rating of 1,477 lbs at maximum air pressure. So the maximum load-carrying capacity of all four tires would be 4 x 1,477 lbs = 5,908 lbs.

tire load index chart

 

Note: The maximum load capacity of the tires may not be their normal capacity. This is because load index ratings are based on the maximum fill pressure of the tire, not the manufacturer’s recommended air pressure level, which is lower.

When replacing your tires, always choose tires with the same or higher load index rating than the Original Equipment (OE) tires. If your car doesn’t have its OE tires, you can find the manufacturer’s recommended load rating in the owner’s manual or the placard on the driver’s side doorjamb.

Most tire installers will not sell or install a lower load-rated tire than the OE recommendation due to liability concerns. This is because if you install tires with a lower load index rating, you’re more likely to overload your tires. Overloaded tires are more prone to damage, blowouts and premature wear.

Read: How to Choose the Right Tires for Your Car

Tire Speed Rating

Like the load index rating, a tire speed rating is another shorthand way to reference how fast a tire can go in ideal conditions. But rather than numbers, it uses letters in (mostly) alphabetical order. (More on that later.)

The tire size in our example had a speed rating of Y. Using the tire speed rating chart below, we can see that a tire with a Y speed rating can safely go up to 186 miles per hour (mph)—the fastest speed on the chart!

tire speed rating chart

Note: Just because your tires can go up to a certain speed does not mean that your vehicle can nor that it is safe to do so. Please follow all posted speed limits.

As mentioned earlier, speed ratings are in mostly alphabetical order, but there are a few anomalies. For example, H is between U and V (a common explanation is that H once stood for “high performance”).

Originally, the V category was the highest possible speed rating (more than 130 mph).

But as vehicles and tires improved, it became necessary to add more letters to accommodate the faster speeds. The V category changed to 149 mph and the Z speed rating was introduced to cover speeds over 149 mph.

Since then, tires have been made that are capable of reaching even higher speeds, leading to the creation of the W and Y speed ratings.

A Z speed rating still appears on some tires sizes (ex: 225/50ZR16 91W). In this case, “ZR” designates a maximum speed capability of more than 149 mph, while W indicates that the tire’s maximum speed is 168 mph.

But unless you own a super-sweet sports car, you probably aren’t in the market for Z-rated tires. The most common speed ratings for passenger cars, light trucks and SUVs are S, T and H ratings.

Check your owner’s manual for your vehicle manufacturer’s recommended speed rating, and always use tires at that rating or higher.

Find the Tire Size You Need at Virginia Tire & Auto

Still not sure what tires you need? Ask a tire expert at Virginia Tire & Auto! We’ll help you evaluate your options and get you the right tire for your vehicle. Shop our tire collection online or drop by any of our 17 locations for a personalized recommendation.

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