Otto Explains — Tyres
What Do the Letters and Numbers on Your Tyres Mean?
Short Answer
In a code such as 205/55 R16 91V, the tyre is 205 mm wide, its sidewall is 55% as high as it is wide, R means radial, 16 is the wheel size in inches, 91 is the load index and V the speed rating. The right pressure comes from your car's manufacturer, not the tyre.
How do you read a size such as 205/55 R16?
Take 205/55 R16. The 205 is the tyre's nominal width in millimetres, measured from sidewall to sidewall. The 55 is the aspect ratio: the sidewall height is 55% of the width, so a lower number means a lower-profile tyre. The R means the tyre has radial construction, and 16 is the diameter of the wheel rim it fits, in inches.
What do the load index and speed rating tell you?
The number after the size is the load index, a code for the maximum load one tyre can carry: 91, for example, means 615 kg. The letter after it is the speed rating, the maximum speed at which the tyre can carry that load: H is 210 km/h, V is 240 km/h, W is 270 km/h and Y is 300 km/h. A tyre marked XL (Extra Load) or reinforced can carry more than a standard tyre of the same size, and should be replaced with an equivalent.
How can you tell how old a tyre is?
Find the TIN (Tyre Identification Number) on the sidewall, which follows the letters DOT. The date code is the four digits at the end of it: the first two are the week of manufacture and the last two the year, so 4714 means week 47 of 2014. The code is printed on one side of the tyre only, so if you can't see it, look at the other sidewall. Knowing a tyre's age is useful when you buy a used car or check your own tyres.
Which other markings are worth knowing?
M+S stands for Mud and Snow, a marking that isn't subject to regulatory winter testing, while the three-peak mountain and snowflake symbol (3PMSF) shows a tested minimum level of winter performance. The small ridges in the tread grooves, 1.6 mm high, are tread wear indicators: Michelin says a tyre worn down to them has reached its minimum tread depth. Legal tread limits vary by country, and this article doesn't state one. The sidewall may also show MAX LOAD and MAX PRESS: these are the tyre's own limits, not necessarily the right figures for your car.
Which pressure and replacement ratings should you follow?
Use the inflation pressures your vehicle manufacturer recommends, usually given in the owner's manual or on a sticker in the driver's door or fuel filler flap, not the maximum printed on the tyre. Replacement tyres may have a higher load index or speed rating than your car's specification, but not a lower speed rating. Before a long journey, tyres are part of the pre-trip checks Otto recommends.
Common Questions
- Is the pressure on the sidewall the one I should use? No. The MAX PRESS figure is a limit for the tyre. Use the pressure your vehicle manufacturer recommends, shown in the owner's manual or on a sticker in the driver's door or fuel filler flap.
- Can I fit tyres with a higher speed rating? Yes. A higher speed rating or load index than your car's specification is acceptable, but don't fit a tyre with a lower speed rating.
- What does XL mean on a tyre? Extra Load. An XL or reinforced tyre can carry more than a standard tyre of the same size, and should be replaced with an equivalent tyre.
- Where is the date code on a tyre? At the end of the TIN after the letters DOT on the sidewall, as four digits. It is printed on one side of the tyre only, so check both sidewalls.