Every tyre has a wealth of technical information moulded into its sidewall — but for most drivers, it looks like an incomprehensible string of numbers and letters. Understanding what these markings mean will help you verify you have the correct tyres fitted and make informed decisions when buying replacements.
The Main Size Marking — For Example: 205/55 R16 91V
This is the most important marking on any tyre, and you will see it prominently on the sidewall. Let us decode each element using 205/55 R16 91V as an example:
205 — Tyre Width
This is the nominal width of the tyre in millimetres, measured from sidewall to sidewall when the tyre is correctly inflated and fitted to the specified rim width. In our example, the tyre is 205mm wide.
55 — Aspect Ratio (Profile)
This is the height of the tyre sidewall expressed as a percentage of the tyre width. In our example, 55 means the sidewall height is 55% of 205mm — approximately 113mm. Low-profile tyres (40, 45, 50 series) have shallower, stiffer sidewalls for a sportier look and feel but a firmer ride. Higher profile tyres (65, 70 series) are taller and more comfortable.
R — Radial Construction
The R indicates this is a radial tyre — the standard construction for all modern passenger car tyres. Virtually all car tyres sold today are radial construction.
16 — Rim Diameter
This is the diameter of the wheel rim that the tyre is designed to fit, measured in inches. Our example tyre fits a 16-inch rim. This must match your wheel size exactly — a 16-inch tyre will not fit a 17-inch rim.
91 — Load Index
This number indicates the maximum load the tyre can carry at its maximum permitted speed. 91 corresponds to 615kg per tyre — meaning the tyre can safely carry up to 615kg. The replacement tyre must have a load index equal to or higher than the original specification.
V — Speed Rating
This letter indicates the maximum speed at which the tyre can safely be used when correctly inflated and under its rated load. Common speed ratings include:
- T — 118mph
- H — 130mph
- V — 149mph
- W — 168mph
- Y — 186mph
The replacement tyre must have a speed rating equal to or higher than the original specification. Fitting a lower speed rating tyre is both dangerous and may invalidate your insurance.
Run Flat Markings
Run flat tyres are identified by various manufacturer-specific codes on the sidewall, including:
- ROF — Run On Flat (Bridgestone)
- SSR — Self Supporting Runflat (Continental)
- RFT — Run Flat Technology (various)
- ZP — Zero Pressure (Michelin)
- EMT — Extended Mobility Technology (Goodyear)
The DOT Code — Tyre Age
Every tyre carries a Department of Transportation (DOT) code on the sidewall. The last four digits indicate the week and year of manufacture — for example, 2419 means the tyre was made in the 24th week of 2019. Use this to check the age of your tyres — most manufacturers recommend replacement after 5-6 years regardless of tread depth.
The EU Tyre Label
Since 2012, all new tyres sold in the EU and UK must carry a label rating them in three categories:
- Fuel efficiency — A to G, with A being most fuel efficient
- Wet grip — A to G, with A being shortest stopping distance in the wet
- External noise — measured in decibels
The wet grip rating is particularly important for safety — choose A or B rated tyres where possible.
Need a Tyre Replacement?
If you need replacement tyres and want to make sure you are getting the correct specification, call Mobi Tyre on 07768 491888. Tell us your vehicle make, model and year and we will supply the correct tyres and fit them at your location across North Wales and border England — available 24 hours a day.
