Tyre compatibility check;

How to read the sidewall

Take a look at the sidewall of your current tyre. Somewhere between the brand name and the load rating you will find a string of numbers like the one below. Every character is meaningful and there is no marketing involved:

205 / 55 R 16   91 V

• 205 - section width in millimetres, measured between the sidewalls when the tyre is correctly inflated and unloaded.
• 55 - aspect ratio (profile). Sidewall height as a percentage of the width. 55% of 205 mm = 112.75 mm of sidewall between the rim and the tread.
• R - construction. R = radial, the standard for every modern passenger and SUV tyre. You may also see ZR on high-speed-rated tyres.
• 16 - rim diameter in inches. Must match your wheel exactly - there is no ±tolerance here.
• 91 - load index. The maximum mass each tyre can carry at the rated pressure. Look it up in the table below.
• V - speed index. The maximum sustained speed the tyre is approved for. Letter-coded - see the table below.

You may also see XL (reinforced sidewall), M+S or 3PMSF (winter qualification), RFT / SSR / ROF (run-flat) and the DOT code (four digits = week and year of production).

What do the numbers on the tyre mean?

Quick-reference tables for the two most useful codes: speed index (a single letter near the size) and load index (two or three digits).

Why ±3% on the rolling diameter?

The outer diameter of the tyre - the rolling diameter - defines how many times the wheel turns over one kilometre of road. The speedometer, the ABS sensors, the stability control and the gearbox shift map all assume the diameter that the manufacturer specified for that car. If you change it noticeably, every one of those systems starts reading a wrong number.

The 3% tolerance is the universally accepted engineering compromise: large enough to give you a meaningful choice of sizes for winter, summer or load-rated alternatives, small enough that the car still drives exactly as the factory intended. Within ±3% you will not notice a difference. Beyond ±3% you start fighting the car.

• Speedometer error - a 5% larger tyre reads 5% slow, so 100 km/h on the dial is really 105 km/h on the road. EU regulation allows a tyre to read up to 10% optimistic but never pessimistic.
• ABS and ESP - wheel-speed sensors compare turns per second across the four wheels. A mismatched diameter on one axle can falsely trigger anti-lock and traction control.
• Suspension geometry - wider tyres change the scrub radius and the load on the wheel bearings. Most manufacturers approve up to one width step (e.g. 195 → 205 mm).
• Clearance - a 3% taller tyre is 6% taller in total sidewall (top + bottom), which can rub on the wheel arch at full steering lock or full suspension compression.

Plus-sizing and minus-sizing - what is it?

Plus-sizing means fitting a larger rim while keeping the outer diameter unchanged. The sidewall gets shorter and the section width usually gets wider - the look is sportier, steering is sharper, but ride comfort drops and the rim is more exposed to kerb damage. Common move from 16" to 17" or 18".

Minus-sizing is the opposite - a smaller rim with a taller sidewall, typically for winter wheels. The taller sidewall absorbs cold-weather pothole impacts better, the rim is cheaper, and winter tyres in smaller diameters are easier to find. Common move down one inch (e.g. 17" → 16") while keeping the outer diameter within ±3%.

The compatibility tool above already filters by the same rim, but you can plus-size or minus-size by picking different rim values and comparing the resulting outer diameters. Stay within ±3% of the factory diameter.

How to use the result

1. Enter the dimension printed on your current tyre - for example 205/55 R16.
2. Read the outer diameter and circumference. Compare them with the value listed for your model in the manual or on the door-jamb sticker.
3. If you want a different size, pick one from the compatibles grid. Each card has a percentage diff from your current diameter - values closest to 0% are safest.
4. Click any compatible dimension to open the catalogue filtered to that size - you immediately see brand, season, speed/load index and price for every SKU in stock.

Frequently asked questions