The two characters at the end of a tyre size, the 91V in 205/55 R16 91V, are the load index and the speed rating. Get either wrong and you may be driving illegally and invalidating your insurance.
Load index
A coded number for the maximum weight one tyre can carry at full pressure. It is a lookup value, not a weight in itself.
- 82475 kg
- 85515 kg
- 88560 kg
- 91615 kg
- 94670 kg
- 97730 kg
- 100800 kg
- 104900 kg
- 1081000 kg
- 1121120 kg
Multiply by four for the total the set can carry, which needs to comfortably exceed your car's maximum laden weight. That figure is on the VIN plate.
Electric cars are heavy. A battery pack can add 300 to 500kg over the equivalent petrol model, which is why so many EVs specify XL or reinforced tyres. Fitting a standard casing because it was cheaper in the same size is a real safety issue.
Van and commercial markings
Vans often show two numbers, like 104/102. The first is the single fitment rating, the second is for twin rear wheels where each tyre carries slightly less because load sharing is imperfect.
Speed rating
The maximum sustained speed the tyre is designed for, as a letter:
- N87 mph
- Q99 mph
- R106 mph
- S112 mph
- T118 mph
- H130 mph
- V149 mph
- W168 mph
- Y186 mph
H sits between U and V rather than in alphabetical order, which is a historical quirk worth knowing when you are scanning a list.
Why it matters below the speed limit
The obvious question is why a UK driver needs a 149mph rating on a road limited to 70. The answer is that speed rating is a proxy for how the tyre is built. Higher rated tyres have stiffer casings and better heat resistance, which affects steering response and stability at any speed, not just near the limit.
More practically, your insurer and the law care. Fitting below the manufacturer's specified rating can be treated as using the vehicle in an unroadworthy condition, and an insurer can use it to reduce or refuse a claim after an accident that had nothing to do with the tyres.
The rules for choosing
- Match or exceedNever go below the load index or speed rating your vehicle specifies
- Same axleBoth tyres on an axle must share the same load index and speed rating
- Higher is fineA higher rating is safe, though usually a stiffer ride and more cost for no benefit
- Winter exceptionWinter tyres may be rated one step lower in some cases, with a speed limit sticker in the cabin
Where to find what your car needs
The placard inside the driver's door frame or the fuel filler flap, or the handbook. That is the authority, not whatever happens to be fitted now, since a previous owner may have fitted the wrong thing.
Or search by your registration on our tyre finder and we will match the right specification automatically.