Tire Load Index Explained: Capacity and Replacement Checks
Learn what a tire load index means, where to find it, why it is not a PSI value, and how to verify replacement-tire load capacity.
Quick answer
The tire load index is a numerical code in the service description that corresponds to a maximum load under defined tire conditions. It is not the tire’s weight, an axle rating, or a recommended PSI. A replacement tire should meet the vehicle manufacturer’s load requirements using tire-specific load information.
Key points
- In 225/60R17 99H, “99” is the load index and “H” is the speed symbol.
- The load-index number must be translated with an applicable manufacturer or standards table.
- Maximum tire load is not the same as GAWR, payload, or towing capacity.
- Pressure and load capacity must be evaluated for the exact tire type and vehicle application.
Where the load index appears
The load index usually appears after the tire size as part of the service description. In 225/60R17 99H, 99 is the load index and H is the speed symbol. Some LT, commercial, trailer, or older tire markings use different conventions, including dual load indexes or load-range markings.
The code is not a direct pound or kilogram value. Use the exact tire manufacturer’s technical data or an applicable recognized table to translate it. Do not guess capacity from the numerical difference between two indexes.
Load index, maximum load, and vehicle ratings
Maximum load rating describes a tire. GAWR and GVWR describe vehicle limits. Payload and towing ratings involve the complete vehicle. These numbers interact, but one cannot be substituted for another or added casually.
FMVSS No. 110 connects vehicle tire selection to axle ratings and vehicle loads. FMVSS No. 139 defines a tire load rating as the maximum load a tire is rated to carry for a given inflation pressure. That “for a given pressure” qualification is why load index should not be evaluated separately from tire construction and approved load-and-inflation information.
Replacement checklist
Use the original vehicle specification as the baseline, then verify the exact replacement.
- Read the original tire size and loading label on the vehicle.
- Check the owner’s manual for minimum load index, speed rating, and tire-type requirements.
- Verify the candidate tire’s complete service description and manufacturer data sheet.
- Confirm its approved wheel-width range and application.
- Use the correct cold inflation recommendation for the approved configuration.
- For towing, heavy loads, EVs, LT conversions, or modifications, obtain vehicle-specific guidance.
Why XL and load range are separate concepts
XL identifies an extra-load passenger tire relative to a corresponding standard-load design. LT tires can use load-range letters. Neither marking lets you invent a new PSI target, and neither should be treated as a universal upgrade.
A higher-looking service description does not resolve wheel fitment, handling, clearance, or vehicle-system requirements. Confirm the complete specification rather than choosing on load index alone.
Frequently asked questions
What does 99H mean on a tire?
99 is the load index and H is the speed symbol. Translate and evaluate them using the tire manufacturer’s data and the vehicle’s replacement requirements.
Is a higher load index always better?
Not automatically. It may provide a higher rated capacity, but the tire still must be approved for the wheel and vehicle and satisfy construction, pressure, size, and handling requirements.
Does load index tell me the correct PSI?
No. It is not a pressure recommendation. Start with the vehicle placard and obtain tire-specific guidance for a changed construction or size.
Is tire maximum load the same as vehicle payload?
No. Tire maximum load is a tire rating under defined conditions; vehicle payload, GVWR, and axle ratings apply to the complete vehicle.
Primary sources
We use US government regulations and consumer guidance for factual claims. Links open the source publisher.
- 49 CFR § 571.139 ↗
Federal load-rating definitions, markings, and tire/rim information.
- 49 CFR § 571.110 ↗
Vehicle load, axle, tire selection, and placard requirements.
- NHTSA TireWise ↗
Consumer tire sidewall and loading guidance.