You’ve decided it’s time to buy new tires. You want something great for turns with great fuel economy that you can take down any trail. As you look through your options, you notice a letter showing each tire’s speed rating.
Why do you need a speed rating? Are you planning on speeding?
The manufacturer determines a tire’s speed rating after putting it through rigorous tests. This letter displays the tire’s maximum recommended speed. Without previous automotive knowledge, the speed rating charts may be confusing.
Read on to learn how to read a speed rating chart and how to better understand your next tire purchase.
When looking at your current tires, you will likely find a series of numbers stamped onto the tire. They’ll look a little something like this:
P 255 / 40 R 18 94 Y
This rating tells you everything you need to know about your tires.
You can also find tire ratings or recommendations in your owner's manual or in the driver’s door, where recommended tire pressures and setup information are easily accessible.
If you purchased aftermarket tires, it’s important to understand your new tire size and pressure.
Different tires are designed to operate at different pressures, and you can also find that pressure listed on the tire sidewall.
The first letter in the series refers to the type of tire you have. In our example, we see the letter “P.” When tires are manufactured for the United States market, they must fall within specified guidelines to be considered P-Metric.
If a tire doesn’t have the P, it may be a Euro-Metric tire based on separate load charts.
Tires may have an LT at the beginning or end of the rating, which indicates they are designed for light trucks. Light truck tires require higher inflation pressures and may not be a good fit for your car.
Numbers following the tire type refer to your tire width. Here, it’s 255. The width is given in millimeters and must match the size of your wheels.
Depending on your wheel size, there is a small range of tire sizes that you can safely mount. Tires that are too large or too small won’t seat correctly. They may distort the road feel or even fall off while driving.
Next, you’ll find the aspect ratio. The sidewall height is given as a ratio compared to your tire width.
Yeah, the tire companies are going to make us do math.
For this example, the tire is 225mm wide with an aspect ratio of 40.
225 * 0.40 = 90 or 90mm
90mm = 3.54 inches
This tire has a sidewall height of 3.54 inches.
Taller sidewall heights allow the tire to flex and move more, making them ideal for off-road or winter use where more traction is needed.
R stands for radial. This is the tire construction method, and radial is the most common method used on passenger cars.
You may find other ratings such as B for bias belt or D for diagonal. If no rating is found, the construction method was probably cross-ply. These ratings refer to how the material is placed together.
18 refers to the rim diameter, which is the size of your wheels.
While rims and wheels are often used interchangeably, the rim is the outer front edge of your wheel. This is where the tire mounts.
Common sizes on passenger car wheels include 15, 17, or 18 inches. Tires fit extremely tightly to your wheel to hold air and be reliable while driving. Your tire size must match your wheel size.
94 refers to your load index, which is how much weight a tire can safely handle.
A tire load index number does not state the weight it can handle in pounds. This number needs to be compared to a tire load index chart.
It’s important to remember that you have four tires on your car, and weight is distributed across them. This distribution is often not equal since your engine and other frontal components weigh a lot compared to the empty rear of the vehicle.
Tires should be rated for the vehicle’s weight, passengers, and gear. More weight should be added when hitting bumps or potholes.
While you should always compare your purchase options to the chart directly, the load index includes:
75 =852 lbs
80= 992 lbs
90= 1323 lbs
95 = 1521 lbs
100= 1764 lbs
When hauling with a trailer, weight is added to your rear axle. It’s important to understand the tongue weight of your trailer, which will be distributed to your rear. You may need specialized towing tires if you use your vehicle for towing.
Y or other letters found after your load index refer to the speed rating of a specific tire.
Even though most vehicles today are expected to drive on highways, many tires remain a limiting factor.
A speed rating is given to the overall construction of a tire during manufacturing and testing. Many passenger car tires will be over-engineered for your safety and to ensure failure is minimalized.
The speed rating for tires was established in Europe, and it is designed to rate any tire from lawnmowers to race cars.
Common speed ratings include:
A=under 25 mph rated as A1 through A8
Y=speeds above 186 mph
Did you notice that H was out of place?
For many years, the max speed rating was considered 149 mph and marked as Z. Tires that exceeded this rating fell within a Z category. As cars improved and the industry was pushed to its limits by a need for racing cars, additional ratings were added.
This is why some letters do not appear on the speed rating chart, like X.
A tire can momentarily exceed its listed limits, but it’s not recommended. If your car has M-rated tires and you accidentally drive 81 mph for a moment, you may not have a failure. If you buy a G-rated tire and drive 70 mph daily, you probably will.
When buying new tires, it’s important to understand your intended use. When tires are manufactured, companies will use a specific blend of rubbers and precisely cut tread patterns to cater to certain uses.
If you know you will only use your car for daily use, you should consider a tire that has a long lifespan and good fuel economy. While these tires may be a bit stiffer than a performance tire, you probably won’t need to rapidly accelerate or take turns with force, so a performance tire may not benefit your needs.
If you know you’ll be taking your truck or SUV offroading from time to time, you should always purchase an all-terrain tire to ensure you get the most out of your ride. All-terrain tires can also be purchased with a soft compound for extreme grip, but keep in mind that soft compound often leads to quick tread wear.
Are your winters packed with snow? You may want to consider getting snow tires for the winter season. Snow tires are extremely soft and provide maximum traction. As temperatures rise, the hot asphalt could lead to accelerated tread wear. It’s recommended that you switch back to all-season tires, which remain ideal for daily driving, even in the rain.
When buying any new tire, you’ll be playing a balance game between grip, longevity, and cost. A soft tire will keep you planted on the road but will wear out quicker, while a more solid tire will last far longer but may be slippery in wet conditions.
Understanding your vehicle's needs will help you be a well-informed shopper. When purchasing tires from a shop, it’s important to choose a retailer you feel comfortable with.
Rent A Wheel allows you to shop online and compare options while using your vehicle’s make, model, and year to ensure you get the tires you need. You can send your new tires to a local RAW dealer to get free shipping, installation, and balancing.
Many new tires purchased through RAW come with warranties. You should always confirm your warranty and remain in communication with your local shop to keep your tires rotated, inspected, and ready for the road.