The Placard Beats the Filter: Reading Tyre Load and Speed Ratings Like a UK Mechanic
Photo: Unknown, Public domain, via Wikimedia Commons
Type your registration into a tyre website and you'll get a confident list of 'guaranteed fits'. Type the size off your sidewall and you'll get hundreds more. Neither tells you the whole story. The only authority on what your car should be wearing is a small sticker most drivers have never read: the tyre placard on the driver's door pillar or the inside of the fuel flap.
Where the real spec actually lives
On most UK cars, open the driver's door and look at the B-pillar. On others, pop the fuel flap. Some list it in the handbook, but the physical sticker is what an MOT tester, insurer or tyre fitter will trust. It gives you axle-specific sizes, load indexes, speed ratings and often a note about extra-load or reinforced construction. It may also list recommended pressures for normal and fully loaded running.
While you're there, find the VIN plate, usually under the bonnet or on the door shut. It carries the plated axle weights in kilograms. Those numbers are the maths behind the load index, and they're the bit most buyers skip.
Size is only a third of the part number
Take a typical marking: 205/55 R16 91V. The first three parts are width, profile and rim diameter. The 91 is the load index, and the V is the speed rating. A 91 tyre can carry 615 kg per corner. A V rating means it's approved up to 240 km/h. Neither number is decorative.
Then there's XL, Extra Load or Reinforced. Same size on the outside, different construction inside. An XL tyre is built to carry more load at the same pressure. If the placard says XL, a standard-load tyre of the same size is not a like-for-like swap, even if the online filter says it fits.
Listings that fit by size, not by specification
This is where bargains get expensive. Say your placard calls for 225/45 R17 94Y XL. A listing offers 225/45 R17 91W at a tempting price. It slides onto the rim, clears the arch and looks right. But 91 is 615 kg per tyre; 94 is 670 kg. Across an axle, that's 1,230 kg versus 1,340 kg. If your rear plated axle is 1,300 kg, the cheaper tyre is overloaded before you've added a boot full of luggage.
Another common trap: the placard says 205/55 R16 94H, and the buyer spots a 91V. The V rating looks sportier, so it must be better, right? No. The speed rating is higher but the load rating is lower. You've upgraded the wrong number and downgraded the one that keeps the sidewall alive on a fully loaded motorway run.
The MOT, insurance and handling consequences
An MOT tester isn't just looking at tread depth. Tyres must be suitable for the vehicle, matched in size and construction across an axle, and rated for the load they're carrying. An under-rated tyre can attract an advisory or a fail depending on how it's presented, and it can certainly give an insurance assessor a reason to question a claim. Fitting a different size or speed rating from the manufacturer's specification can also count as a modification if you haven't told your insurer. That's a conversation worth having before the claim, not after.
Handling-wise, mixing a standard-load front tyre with an XL rear, or a 91 on one side and a 95 on the other, creates a car that behaves differently corner to corner. Same size, different construction, different flex. On a damp roundabout, that's not a theoretical problem.
The load-index maths you can do on the driveway
Grab the VIN plate and find the plated axle weights. Divide each by two to get the minimum load per tyre, then add a sensible margin for passengers, fuel and towbar nose weight. Compare that to the load index table: 88 is 560 kg, 91 is 615 kg, 94 is 670 kg, 97 is 730 kg, 100 is 800 kg.
Example: a rear axle plated at 1,320 kg needs at least 660 kg per tyre. A 94 rating at 670 kg just clears it; a 91 at 615 kg does not. The placard already did this maths for you, which is why it lists the 94 in the first place.
For speed rating, the tyre must meet or exceed the car's maximum speed. Winter tyres can sometimes run a lower speed rating with a sticker in the driver's view and within the tyre maker's limits, but don't assume that applies to a summer tyre. If the placard says V, don't fit H and hope for the best.
A five-minute pre-order cross-check
- Photograph the placard and the VIN plate. Keep both on your phone.
- Write down the axle-specific size, load index, speed rating and whether XL is specified.
- Look at what's currently fitted. If it doesn't match the placard, ask why before you repeat the mistake.
- Read the full listing spec, not just the size in the title. Check the load index and speed rating appear in the product details.
- Check the DOT date code on the sidewall: four digits, week and year. Rubber has a birthday.
- If your car runs TPMS, factor in new valves or service kits where needed.
The bottom line
The online filter is a starting point. The placard is the contract. Buy the whole part number, not the headline size, and you'll avoid the quiet overload that eats sidewalls, muddles insurance claims and makes a well-sorted car feel vague. Size gets you in the door; load index, speed rating and construction keep you legal, insured and planted.
