All tires have tire descriptions written on the sidewall. These consist of a series of letters and numbers which could look something like one of these:
- P225 / 60 R16 94T
- P205 / 55 R19 92S M+S
- 215/45R17 91V
To most people, these are just a meaningless array of letters and numbers, however to the informed mechanic or car enthusiast they provide crucial information about the expected performance and suitability of the tire for any given vehicle.
Whether you are looking for a smooth silent tire or something that will improve your vehicles handling and performance understanding tire descriptions can help you get the best out of your vehicle.
Using P225 / 60 R16 94T as our example, let’s break it down and find out what the numbers and letters actually mean:
Service Description – P225 / 60 R16 94T
The letters at the start of your tire description indicate the vehicle service type. Not all tires will use a service description letter. However, of the tires that do use it, it will be one of the following four:
- P: Passenger – These tires are what you would find on your ordinary everyday passenger vehicle that accounts for 90% of vehicles on the road.
- LT: Light Truck – These tires are designed for use on pickup trucks or transit vans weighing up to 8,500lb (3,855kg) with a maximum payload of a 4,000lb (1,815kg).
- ST: Special Trailer – Special trailer tires are designed for use on towed trailers, they typically have 10% more weight capacity than light truck tires and 40% more than passenger tires. They are also designed with extra stiff tire walls to help keep them stable preventing your trailer and it’s load from swaying.
- T: Temporary – Theses are for temporary use only. They are not designed for high speeds and have a low load-bearing capacity (this means they can be smaller and fit more discreetly in your car) they are typically restricted to no more than 50kmh.
Tire Width – P225 / 60 R16 94T
The first number in your tire description simply tells you how wide the tire is in millimeters. In our example the tire is 225mm wide, this is a very common tire width.
The wider your tire the better they will handle and the smoother they will feel through corners. They will also handle better in icy conditions.
Wider tires have more surface area in contact with the floor making them ideal for powerful cars (have a look at how wide the tires are on Formula 1 cars!).
For most of us who don’t drive any faster than the speed limit, tire width isn’t something we need to be too concerned about as standard-width tires will be more than adequate.
Aspect Ratios – P225 / 60 R16 94T
The second number in a tire description is the aspect ratio.
The aspect ratio tells us how high the sidewall of the tire is.
This number works as a percentage of the tire width, in our example, it is 60%. The sidewall, therefore, is 60% of 225 giving the sidewall a height of 135mm.
The higher the aspect ratio the more comfortable your ride is likely to be. A higher aspect ratio means that the tire has more ‘air space’ therefore allowing it to absorb more of the impact when you go over any bumps.
Be aware that a high aspect ratio may reduce the handling of your vehicle. Performance vehicles tend to have low aspect ratios because having a short sidewall means the tire can stay stiff and resist cornering forces better.
Construction Type – P225 / 60 R16 94T
Not all tires will give you a construction type letter. If your tire does include a construction type letter it will be one of:
- B – Bias Belt – These feature a belt which is made from steel or fiberglass which sits directly under the tire tread to prevent punctures.
- D – Diagonal – These are made from layers of nylon cord which overlap each other diagonally at a 55-degree angle.
- R – Radial: These are made using a design where the cords inside the tire run at 90 degrees to the direction of travel.
Almost all tires are made using radial construction these days. B & D types of tires are now very rare.
Rim Diameter – P225 / 60 R16 94T
This number tells you what size trim the tire is designed to fit. If you get this wrong then the tire simply won’t fit your car!
Bigger rims on a car can cause your ride to be less comfortable than smaller rims however big rims often increase the value of your car as they are considered to be more aesthetically appealing.
Load Index – P225 / 60 R16 94T
Your tires load index number gives corresponds to a maximum weight that your tire can support when inflated.
Presuming all your tires have the same load index then the maximum weight your vehicle can carry without damaging the tires is 4x your tires load index (providing the weight is evenly spread throughout your vehicle):
|Load Index||Max Weight|
|75||852lb / 386kg|
|100||1764lb / 800kg|
|125||3638lb / 1650kg|
|150||7385lb / 3350kg|
Check out this article for a full break down of load indexes.
Speed Rating – P225 / 60 R16 94T
The final part of your tire description is the speed rating, this letter corresponds to the maximum speed that your tire is capable of maintaining.
Speed ratings range from L to Y:
|Speed Rating||Max Maintainable Speed|
|L||120 kmh / 75 mph|
|M||130 kmh / 82 mph|
|N||140 kmh / 87 mph|
|P||150 kmh / 93 mph|
|Q||160 kmh / 99 mph|
|R||170 kmh / 106 mph|
|S||180 kmh / 112 mph|
|T||190 kmh / 118 mph|
|U||200 kmh / 124 mph|
|H||210 kmh / 130 mph|
|V||240 kmh / 149 mph|
|W||270 kmh / 168 mph|
|Y||300 kmh / 186 mph|
Your vehicle manual will recommend a speed rating which your car should use. Make sure you don’t use a tire which has a lower speed rating than what your manual recommends (it is okay to use a higher one though be aware that they are often much noisier) because if you do so and are in an accident then your insurer can refuse to pay out.
We hope this guide has helped you get to grips with tire descriptions so that next time you are looking to buy a set you know what you are looking for.