What Do Load Index and Speed Rating Mean on a Tire?

The load index is a number that corresponds to the maximum weight one tire can support when properly inflated. The speed rating is a letter for the maximum service speed of the tire. In a marking such as 205/55R17 91V, 91 is the load index and V is the speed rating (sources: Michelin, Just Tires).

Michelin says the speed rating should always meet or exceed the vehicle manufacturer's specification. For your own vehicle, ask a tire technician or check the owner's manual.

What does the load index number mean?

Just Tires describes the load index as an assigned number that corresponds to the maximum weight a tire can support when properly inflated. Michelin gives the same meaning and uses the example 205/55R17 91V, where 91 is the load index.

Michelin states that a load index of 91 means the tire can support up to 615 kilograms. That is about 1,356 pounds (calculated conversion). Just Tires lists index 90 as 1,323 pounds and index 100 as 1,764 pounds, so a higher number means a higher load capacity.

Michelin says it is permitted to install a tire with a higher load rating, but this does not increase the vehicle's allowable load. The load limit of the vehicle stays what the manufacturer specifies.

What does the speed rating letter mean?

The letter after the load index is the speed rating. Just Tires lists these maximum speeds:

Michelin gives values in kilometers per hour: H-rated tires are rated to 210 km/h and V-rated tires to 240 km/h (149 mph). Just Tires adds that a speed rating is not a recommendation to exceed speed limits, so obey all posted limits.

What should you match when you replace tires?

• Meet or exceed both ratings. Michelin says to meet or exceed both the load rating and the speed rating, and never go lower. It warns that lower ratings may affect insurance coverage after an accident.
• Equal or higher speed rating. Just Tires says to replace a speed-rated tire with one of an equivalent or greater rating. Its example: if V is recommended, V, W, Y or Z are acceptable.
• Do not mix speed ratings. Just Tires says not to mix tires with different speed ratings. If you must, it says to install matched pairs on the same axle, and the vehicle's speed capability is then limited to the lowest-rated tires.
• Same size is not the same rating. Michelin notes that tires with the same dimensions may have different load or speed ratings, so check both on the sidewall.
• Winter exception. Michelin says a lower speed rating is not advised unless the tires are winter-capable (3PMSF emblem). In that case, the vehicle must be kept below the tire's maximum rated speed.

For tire size and inflation pressure, NHTSA says to check your owner's manual or the Tire and Loading Information Label on the driver's door edge or post. It gives no load index or speed rating figures, so confirm those with the manual or a tire technician. For the other numbers in a size marking, see how to read a tire sidewall. To compare overall dimensions of two sizes, use the tire size calculator.

Frequently asked questions

Where do I find the load index and speed rating on my tire?

They are the last part of the size marking on the sidewall, after the rim diameter. In 205/55R17 91V, the number 91 is the load index and the letter V is the speed rating (Michelin).

Can I fit a tire with a higher load index?

Michelin says it is permitted to install a tire with a higher load rating, but it does not increase the vehicle's allowable load. Check the vehicle manufacturer's recommendation or ask a tire technician.

Can I fit a tire with a lower speed rating?

Michelin says the speed rating should always meet or exceed the vehicle manufacturer's specification, with a limited exception for winter-capable tires. Ask a tire technician before choosing a lower rating.

Sources

• Michelin Canada: Tire Load Rating & Speed Rating Explained
• Just Tires: Load Index Speed Rating
• NHTSA: Tire Safety and Maintenance