What Tire Load Index Do I Need? Finding the Required Capacity

What the specification means

The load index is the two- or three-digit number in the service description that follows the tire size. In a marking such as 225/65R17 102H, 102 is the load index and H is the speed rating. Each index number corresponds to a fixed maximum load per tire in a standardized table. For example, index 91 equals 615 kg (1,356 lb), index 100 equals 800 kg (1,764 lb) and index 102 equals 850 kg (1,874 lb). The sidewall also prints the maximum load in pounds and kilograms next to the maximum pressure, so you can confirm the figure without a table.

That rated maximum is per tire, and it applies only at the inflation pressure the standard specifies for that tire's construction. At lower pressure, the tire carries less. A set of four tires rated at 1,764 lb each does not mean the vehicle may weigh four times that amount, because the vehicle's own weight ratings remain the controlling limit.

A common question is whether the load index includes the weight of the vehicle. It does, in the sense that the tires support everything resting on them: the vehicle itself, passengers, cargo and any trailer tongue weight. That load is not split evenly. Engine placement, body style and what you carry shift more weight onto one axle, which is why manufacturers set tire capacity from axle ratings rather than total weight divided by four.

Identify the applicable version

A single model name can cover several original tire sizes and load indexes. Trim level, wheel diameter, two-wheel versus four-wheel drive, cab and bed configuration, engine choice, towing or heavy-duty packages and model-year updates can all change the specification. A tire that suits a base sedan may be undersized for the same model on larger wheels, or for its wagon or crew-cab variant.

Work from your exact vehicle: the model year, the VIN and the labels physically attached to it. Avoid broad lookups by model name alone. If the vehicle has aftermarket wheels, a lift kit or tires installed by a previous owner, treat the current tires as unverified. They show what was fitted, not what the vehicle requires.

Read the correct specification

Start with the tire and loading information placard, usually on the driver's door jamb and occasionally on the door edge, fuel filler door or glovebox. It lists the original tire size for the front, rear and spare, the recommended cold inflation pressure, the seating capacity and the maximum combined weight of occupants and cargo. Some placards include the full service description with the load index; others show only the size. In that case, check the owner's manual, the sidewall of the original tires if they are still fitted, or a dealer lookup by VIN.

The federal certification label nearby lists the gross vehicle weight rating (GVWR) and the gross axle weight ratings (GAWR) for front and rear. These figures let you work out the requirement yourself, which is all a tire load index calculator really does. Divide each axle's GAWR by two to find the minimum capacity each tire on that axle must provide, then compare that figure to the load index table. As an illustration, if a front GAWR were 3,500 lb, each front tire would need at least 1,750 lb of capacity, so an index of 100 at 1,764 lb would just clear it.

Treat that calculation as a cross-check, not a replacement for the original specification. The practical answer to how to determine your tire load index is simple: choose a replacement whose index is equal to or higher than the original equipment value, even if the axle math suggests a lower number would be enough.

Apply the limits correctly

Inflation pressure decides whether a tire actually delivers its rated capacity. With original-type tires, use the cold pressure on the vehicle placard, not the maximum pressure molded on the sidewall. If you change load type, such as moving from a standard-load tire to an extra-load or reinforced tire, or between P-metric and Euro-metric sizing, the pressure needed to carry the same load can differ. Use the tire manufacturer's load and inflation table to set it. Underinflation reduces capacity and builds heat, which is the main way an adequately rated tire ends up overloaded.

Tire type also changes the usable value. When P-metric passenger tires are used on a light truck, SUV or van, industry practice reduces their rated load by dividing it by 1.10. The vehicle manufacturer has already accounted for this on original equipment, but it matters if you switch tire types. LT tires carry two indexes, such as 121/118, for single and dual mounting, along with a load range letter. Use the dual figure for dual rear wheels. Replacing LT tires with P-metric tires on a truck often loses capacity even when the size looks the same.

Keep tires on the same axle identical in size, load index and construction. On all-wheel and four-wheel drive vehicles, drivetrain compatibility also depends on keeping tire size and tread depth closely matched across all four positions, within the manufacturer's tolerance. A higher load index in the correct size is generally acceptable, but do not trade away the original speed rating to get it. Fitting tires with more capacity never raises the vehicle's GVWR or GAWR.

A short verification checklist

Before buying tires, confirm the model year, trim, drive configuration and wheel size using the VIN and the vehicle's own labels. Record the original tire size, load index and speed rating from the placard or owner's manual, along with the front and rear GAWR from the certification label. Then check that each candidate tire's load index is at least the original value, that its capacity at your intended inflation pressure covers half of the heavier GAWR, and that its load type and speed rating match or exceed the original.

Before loading or towing, add up occupants, cargo and trailer tongue weight and keep the total within the placard's combined limit. Set cold inflation pressure to the specification for the tires actually fitted, and inspect tread depth and sidewalls for wear, cuts or bulges. If anything about the size, load type or pressure is uncertain, resolve it with the vehicle or tire manufacturer's published data before driving with a heavy load.