225/65R17 102H. Everything after the size is the service description, and it's doing two jobs at once: 102 is the load index (the tire carries 1,874 lb max), and H is the speed rating (certified to 130 mph). Here's how to read the whole system, compute the minimum index your vehicle actually needs, and avoid the P-metric derating trap that quietly costs trucks and trailers ten percent of their capacity.
A coded maximum, set by the ETRTO and Tire & Rim Association, for how much weight one tire can carry at its maximum inflation pressure. It's a lookup, not a formula — each step doesn't add a fixed number of pounds, which is why you need the chart. The everyday range for passenger vehicles runs from about 75 (853 lb, subcompacts) through 104 (1,984 lb, half-ton pickups), while hard-working LT and trailer tires climb to 121 (3,197 lb) and beyond.
Two rules govern everything else. Multiply a single tire's rating by four to get your tires' total capacity, and that total must beat your vehicle's fully loaded weight. And never fit a lower index than the one printed on your door-jamb placard — the manufacturer already did the math for the worst case.
| Index | Per tire | Set of 4 | You'll see it on |
|---|---|---|---|
| 91 | 1,356 lb | 5,424 lb | Compacts and crossovers |
| 95 | 1,521 lb | 6,084 lb | Small SUVs |
| 102 | 1,874 lb | 7,496 lb | 3-row SUVs, light pickups |
| 104 | 1,984 lb | 7,936 lb | Half-ton pickups |
| 110 | 2,337 lb | 9,348 lb | Heavy-duty pickups |
| 121 | 3,197 lb | 12,788 lb | LT truck & trailer tires |
The full chart with every index from 71 to 126 — in pounds and kilograms — lives in the tool below.
Type a service description (102H, 121S) or pick an index, and get per-tire capacity, the four-tire total, and the speed rating. The vehicle tab computes your minimum index.
Tire Load Index Chart & Calculator →One division: (curb weight + people + cargo) ÷ 4, then pick the index that clears it. Example: a 4,400 lb SUV carrying 1,200 lb of family and luggage sits at 5,600 lb gross, or 1,400 lb per tire. Index 92 (1,389 lb) fails; index 93 (1,433 lb) passes. The factory 102s carry 34% headroom over that requirement — exactly the margin a loaded vacation trip or a roof box full of gear eats into.
For trucks that tow, run the same math on the truck's own loaded weight (not the trailer's — trailer tires carry the trailer's weight). And when a placard specifies LT tires, replace with LT: the door placard assumed the higher pressures and reinforced construction.
The letter certifies sustained-speed durability: S = 112 mph, T = 118, H = 130, V = 149, W = 168, Y = 186. Since US speed limits sit far below even the lowest ratings, the practical meaning isn't legality — it's that higher-rated tires use stiffer construction that changes steering response, and that running the rated speed on an underinflated or overloaded tire is how heat failures happen. Match the letter across all four corners; mixing front-to-rear handling characteristics is how a budget upgrade becomes a handling downgrade.
Same size, same printed load index, different reality. A P235/75R15 carries 1,984 lb — but only at 35 psi, and only in passenger-car duty. Fit it to a pickup, a hauling SUV, or a trailer, and the standards require dividing its capacity by 1.10: 1,984 → 1,804 lb. Meanwhile the LT235/75R15 in load range C carries 1,985 lb at 50 psi, no derating, with sidewalls built for the abuse. On paper the tires look identical; in truck service the LT simply carries more, longer, hotter.
The load-range letters on LT tires map to the old ply ratings: B = 4-ply at 35 psi, C = 6-ply at 50, D = 8-ply at 65, E = 10-ply at 80, F = 12-ply at 95. If your truck placard says LT with a load range, that letter is part of the spec — an "equivalent" P-metric isn't.
It's the service description: load index 102 and speed rating H. The tire carries a maximum of 1,874 lb (850 kg) at its maximum inflation pressure, and is certified for sustained speeds up to 130 mph. Four such tires support up to 7,496 lb.
Take your vehicle's curb weight, add passengers and cargo, and divide by four — each tire needs a rating above that per-tire number. A 5,600 lb loaded SUV needs 1,400 lb per tire, so load index 93 (1,433 lb) is the floor. In practice, just match or beat the index on the door-jamb placard.
Tire and Rim Association standards require P-metric max load to be derated by dividing by 1.10 (about 9%) when the tire is fitted to a light truck, SUV used for hauling, or trailer, because those duty cycles are harsher than the passenger-car standard the rating assumes. A P235/75R15 rated 1,984 lb becomes about 1,804 lb in truck service — often less than the same-size LT tire it replaced.
Divide the trailer's fully loaded gross weight by the number of tires. A 7,000 lb tandem-axle trailer needs 1,750 lb per tire — load index 100 minimum, though ST tires are usually chosen by load range instead. Never fit passenger tires to a trailer; special trailer (ST) tires have stiffer sidewalls built for that duty.