Understanding Tire Service Descriptions: Speed Rating and Load Index
There never seems to be a shortage of questions you are asked when you inquire about tires. What size do you need? What speed rating do you require? How will you be using them? What load index do you need?
Where do you find this information, and what does it even mean? It may seem overwhelming, but knowing a few key pieces of information will help you find the correct tire for your vehicle.
Where to find Load Index and Speed Rating on your tire
On the sidewall of your tire, your tire size is indicated in the format of 215/60R16. Immediately following the tire size is another number and a letter like 94S. This is the load index and speed rating of your tire. Let’s decipher it.
The number is the load index. It indicates how much weight the tire can bear. The higher the load index number, the more weight it can carry:
Example Load Index Chart
As you can see, the number 94 means each tire can bear up to 1,477 lbs of weight, or 670 kg. The load index of your tires shouldn’t be reduced. A tire is matched precisely to a vehicle when it is engineered. Using a tire with a lower load index could result in undesirable tire wear or failure. You may choose to use a load index higher than your vehicle was originally equipped with, and the load capacity will increase.
Beside the load index is a letter which indicates the speed rating. In our example the letter is S. As with the load index, the higher the letter in the alphabet, the higher the speed rating:
Example Speed Rating Chart
The speed rating is the maximum speed a tire can be operated up to. A tire’s speed rating is void if it has been punctured, patched, or otherwise damaged. The manufacturer can no longer guarantee the safe operation of the tire at high speed.
High Performance Speed Rating
High performance tires have a speed rating in a slightly different fashion. In the tire size, the addition of a Z indicates it is a tire capable of speeds in excess of 149 mph. It is shown as:
That was thought to be as much rating as was needed, and the Z rating encompassed all tires rated at 149 mph and higher. Since the inception of Z-rated tires, further clarification has occurred that identified specific speed ratings for above-149 mph speeds. W-rated tires indicate a tire capable of speeds up to 168 mph, and Y rated tires up to 186 mph. Anything beyond Y rated tires is shown with the load index/speed rating in parentheses. For example, it could be shown as (99Y).