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Tire Speed Rating and Why It Matters

When it comes to your car, understanding your tire speed rating and why it matters is important! The tire speed rating is the max speed the tires can safely carry a load for a length of time in ideal conditions. This is the original weight of the car plus whatever is inside the car to make it heavier. You can find the rating of your tire speed on the tire sidewall; it’s molded to it and is signified by a letter or two after a load index number. With the load index number and speed rating together, you get the service description for your tires. There is a standard chart to follow with your tires and each letter in your tire speed rating represents a max speed.

Things To Know About Your Tire Speed Rating

When it comes to your tire speed rating, there are a few things that you really need to know to know why it matters so much:

  • The higher the alphabet placement on the tire, the better it will be able to handle fast speeds and high heat. This is different for H-rated tires.

  • The speed capacity of the car may be less than the rating on the tire, which is where this can get confusing! The rating on the tire shows the performance in a controlled setting rather than the open road. 

  • The condition of the tire, the inflation level, the extra cargo, the weather and the surface on which you are driving are all everyday limits that help to decide the maximum safe speed of the tires.

  • If your tires on your vehicle have different speed ratings, the limit of the tire with the lowest marked rating is how fast you are allowed to drive. This is optimum for the capability of your tires and avoid an accident.

  • The most common speed ratings for cars are S and T, as these ratings cover sedans, minivans and light trucks.

How Are Tire Speed Ratings Chosen?

A tire manufacturer will use thorough testing to decide the tire’s capacity for heat and speed. They use a testing machine specifically to meet the ECE standards. This scale used is based on km/h and there are sometimes more rigorous tests done to meet the Society of Automotive Engineer tire standards. The ECE standard test involves the tires being inflated properly and mounted on a wheel. This is then added to a testing machine in a room with a 77F temperature. The tire is pressed down onto a metal drum to mimic a car with a realistic loading. The tire is then spun for 10 minutes at higher and higher speeds until it hits the target speed. It spins for a further ten minutes here and is then inspected at stop for any failures - such as issues with the tread. A tire passes the speed rating if it’s still intact at this point.

If the tire performs at the right level, the Step-Up Speed test is sometimes used and this will involve increasing the tire speed until the tire fails entirely!

Why Tire Speed Ratings Matter

You need to ensure that you - and others - are as safe on the road as possible. Tires with a higher speed rating often have better handling benefits to offer, which is attractive for some drivers. The problem is that these are tires with softer rubber and a stiffer construction, which means that they can steer and corner really well, but they’re not as comfortable and offer a lower performance in other conditions. They also often have a much shorter tread life.

 

Your tire speed rating is based on lab simulations, which means that there are no real-life situations accounted for in determining speed rating safety. It’s important not to just look at the tire speed rating as the top speed guideline. If your car or van is carrying a heavier load, or your tires have been on for a while, your capacity to speed up won’t be the same as it was brand new. Being safe in your driving efforts is important, so make sure that you drive the speed limit or below in precarious conditions. 


Your tire speed rating matters for the type of car or van you have, but it’s always important to explore your speed limitations elsewhere, too. Make sure that you are aware of your tire speed rating and check when your tires were last serviced. Calling us today at Dixie 4 Wheel Drive is a great decision - let us check your tires for you today!


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