What Is Load Index?
A tire's load index is a standardized numerical code representing the tire's maximum load-carrying capacity under specified conditions. It is normally shown on the tire sidewall as a number after the tire size, such as 225/45R17 94W. In this example, 94 is the load index and W is the speed rating.
Load index is not a weight measurement by itself. The number must be matched to a load-index table to determine the corresponding capacity, usually expressed in kilograms (kg) or pounds (lb). The capacity is for one tire.
How Load Index Is Used in Tire Fitment
When selecting tires for a target vehicle, the replacement tire's load index should normally meet or exceed the vehicle manufacturer's required rating. The requirement may be listed on the vehicle tire-information placard, in the owner's manual, or in a verified fitment specification.
For example, a tire with load index 94 is rated to carry up to 670 kg per tire under the conditions associated with that rating. Four tires with that rating have a theoretical combined capacity of 2,680 kg, but this does not automatically mean the vehicle may be loaded to that amount. The vehicle's own gross axle and gross vehicle weight limits still apply.
Load index matters particularly when changing wheel diameter, wheel width, or tire size. A replacement tire can have the correct outside diameter and still be unsuitable if its load capacity is too low. Tire clearance and handling characteristics must also be checked as part of the complete tire package.
Common Load Index Examples
The following are examples from the standard load-index scale:
| Load index | Maximum load per tire |
|---|---|
| 91 | 615 kg / 1,356 lb |
| 94 | 670 kg / 1,477 lb |
| 100 | 800 kg / 1,764 lb |
| These values are useful for explaining the rating, but the correct tire choice depends on the vehicle's required rating, inflation pressure, tire construction, and operating conditions. The complete load-index table should be used when checking a specific tire.
Load Index vs. Speed Rating
Load index and speed rating are separate parts of the tire service description:
- Load index indicates the tire's rated load capacity.
- Speed rating indicates the tire's approved maximum speed category under specified test conditions.
A tire may have an adequate load index but an unsuitable speed rating, or the reverse. Both ratings should be checked rather than treating one as a substitute for the other.
Load Index vs. Wheel Load Rating
Tire load index describes the tire. It does not describe the wheel's maximum load rating. A wheel also needs to be capable of carrying the intended vehicle load, and the wheel's mounting hardware and fitment must be correct.
A wheel-and-tire package can therefore fail fitment checks even when the tire load index is adequate. Bolt pattern / PCD, center bore, wheel width, offset, brake clearance, suspension clearance, lug hardware, and vehicle configuration may also determine whether the package is a Direct Fit or requires further checking.
Common Fitment Mistakes
- Treating the load index as a weight in kilograms. A rating such as 94 is a code; it does not mean 94 kg.
- Checking only the tire's physical dimensions. Matching diameter and width does not prove that the tire has sufficient load capacity.
- Confusing load index with speed rating. The number and letter communicate different properties.
- Using the axle capacity as the tire requirement. Load index applies to each tire, while the vehicle also has separate axle and gross-weight limits.
- Assuming a higher load index solves every fitment issue. A higher-rated tire may still have unsuitable dimensions, clearance, construction, or handling characteristics.
- Ignoring inflation pressure. A tire's load capacity depends on the pressure and conditions specified for that tire; it should not be loaded beyond its rating.
What to Check Before Changing Tires
Before fitting a new tire package, compare the proposed tire with the vehicle's required specification:
- Confirm the load index and speed rating.
- Check the tire size, approved rim-width range, and overall diameter.
- Make sure the wheel is correctly matched to the tire and has sufficient load capacity.
- Verify clearance at the brakes, suspension, wheel well, and bodywork.
- Confirm that inflation pressures follow the vehicle and tire-maker requirements.
A tire with an equal or higher load index is generally the appropriate starting point, but complete tire and wheel compatibility still requires checking the rest of the fitment details.