How to read your tyre size in 60 seconds

The five numbers that matter

Take 205/55R16 91V. The 205 is the tread width in millimetres. The 55 is the aspect ratio: the sidewall height is 55% of the width. The R means radial construction, which every modern car tyre is. The 16 is the rim diameter in inches. The 91 is the load index and the V is the speed rating.

Those last two are the ones people ignore, and they are the ones that matter most for safety. Load index 91 means each tyre can carry 615kg. Speed rating V means it is rated to 240km/h — not because you will drive that fast, but because the rating reflects how much heat the casing can handle over sustained running.

Where to find your correct size

Three places. The sidewall of the tyre currently fitted, the placard inside the driver's door frame, and the owner's manual. If those three disagree, the door placard wins, because that is the manufacturer's specification for your exact vehicle.

Be careful with used imports: the previous owner may have fitted a different size. That is why we always check the placard rather than simply matching what is on the car.

Can you change size?

Yes, within limits. Overall rolling diameter should stay within about 3% of standard, or your speedometer reads wrong and, on modern cars, ABS and traction control calculations drift.

Going wider adds grip but costs fuel and can rub on full lock. Going to a lower profile sharpens steering but exposes the rim to pothole damage — a real consideration in Nairobi. We will run the numbers with you before you commit.

If any of this raises a question about your own car, bring it in. The tyre safety check is free and takes ten minutes, and we will give you a written summary whether or not you buy anything.