Tire Load Index Calculator

Tire load index is a number on the tire’s sidewall that corresponds to the maximum weight each tire can support when properly inflated.
It is part of the tire size code. In 225/65R17 102H, the “102” is the load index and “H” is the speed rating.

Why it matters:

If your vehicle is loaded beyond the tire’s capacity, the tire can overheat, deform, or fail, and that failure is usually a blowout rather than a slow leak.
This matters most when hauling cargo, towing, or carrying a full car of passengers and luggage.

One thing the index does not tell you: the rating only holds at the tire’s stated maximum inflation pressure. Run the same tire 8 PSI low and you lose a meaningful slice of that capacity, which is why an overloaded trailer on soft tires is such a reliable way to shred a sidewall.

Load index table (key values):

Full Load Rating formula:

Total capacity (4 tires) = Single tire capacity × 4

Your vehicle’s GVWR (Gross Vehicle Weight Rating) should never exceed the combined tire capacity. Check the sticker inside your driver’s door jamb for your vehicle’s GVWR.

Speed rating letters (on the same sidewall):

Never exceed your tire’s speed rating. It is a heat limit as much as a speed limit, so a sustained fast motorway run on an underrated tire is the dangerous case, not a brief overtake.

Reading a full tire code:

225 / 65 R 17 102 H

• 225 = section width in mm, measured at the widest point of the tire rather than across the tread blocks
• 65 = aspect ratio (sidewall height = 65% of 225 mm)
• R = radial construction
• 17 = rim diameter in inches
• 102 = load index
• H = speed rating

Checking your own vehicle: the tire placard inside the driver’s door jamb gives the GVWR (Gross Vehicle Weight Rating) and the load index the manufacturer specified. Fitting a lower index than the placard calls for is the mistake to avoid, and it is easy to make by accident when a shop substitutes “an equivalent size” that matches on width and diameter but not on load.