Learning your letters
When you look at tyres on most vehicles, you’ll see a variety of letters, numbers, symbols & words. It can all look a bit like a foreign language and it can be difficult to know exactly what it all means, especially when you’re about to drop a few hundred bucks on a new set of tyres for your car.
If you’re looking to find out what it all means, you’re in the right place. We’ve put together this short guide to help you understand tyre terminology.
The general terms
We’ll start off with some of the general terms you’ll hear that apply to all tyres. While there are over 100 different terms used to describe various parts of the tyre. We’ll focus on the most commonly used.
The tread is the raised part of the tyre that makes contact with the road. The tread is responsible for channeling water away from the tyre to allow better grip in wet weather conditions.
This runs around the inside of the tyre on both sides, and is the part of the tyre that makes contact with the rim. Wheels have a small groove into which the bead slots, and the air pressure inside the tyre makes sure your tyre doesn’t pop out.
This is the vertical side of the tyre between the tread and the bead. You’ll find all your tyre’s specific information & performance details on the sidewall.
This is the fundamental structure of the tyre, and it is responsible for taking up to 80% of the stresses experienced by a tyre. It consists of rubber-coated fibers that are bonded to the bead to keep the tyre’s shape & strength.
The sidewall details
These are the details you’ll find printed on the side of every vehicle tyre. While they may seem random and non-sensical to you, they actually give you a lot of information about the tyre’s dimensions, performance capabilities, construction & limits.
This one is a bit of a no brainer: this is the width of the tyre in millimetres. As a result of being measured in millimetres, this is a three-digit number and you’ll find it at the beginning of all the numbers & letters you see on your tyre.
The aspect ratio of a tyre is sometimes known as the profile. It’s a measure of how tall the tyre’s cross section is compared to the tyre’s width.
For example, a tyre with an aspect ratio (or profile) of 55 means that the tyre’s height is equal to 55% of its width. Putting that into numbers, if your tyres are 200mm wide with an aspect ratio of 55, then this means your tyre’s height is 110mm.
Tyres with a low aspect ratio are frequently known as low-profile tyres, and are often found on high-end cars or non-factory-stock rims. While less common, you can also find high-profile tyres with higher-than-normal aspect ratios, generally found on vehicles that need to support a higher weight or take more punishment, such as truck tyres or off-road tyres.
Tyres can be built in two ways: Radial and Cross-ply.
Unless your regular ride is a Ford Model-T or something vintage, you’ll rarely come across a cross-ply tyre.
For that reason, almost all the tyres you’ll see for your vehicle will have the letter ‘R’ written on the sidewall after the aspect ratio, which denotes Radial construction.
Rim or wheel diameter
Unlike the width of the tyre, the rim diameter is measured in inches. This measurement tells you what size of rim for which the tyre is made.
The load index is the maximum weight that a single tyre can support. The number isn’t the weight itself, but represents the weight. For example, a load index of 95 means a tyre can support up to 690 kg.
Load Indexes range from 51 (195kg) to 250 (60,000kg). Unless you’re planning on transporting very heavy goods regularly, you’ll rarely need to consider load index.
The speed rating is a letter that represents the speed at which a tyre can be used before it becomes unsafe or unsuitable. The letters range from E, which represents a speed of 70km/h, up to Y, which is safe up to 300km/h. Most passenger car tyres start at N (140km/h).
Similar to Load Index, it’s unlikely you’ll need to worry about speed rating unless you’re planning on taking your car to track days or race events.
The tyre type can appear in a couple of different places depending on the tyre, and is represented by the letters T, P, or LT.
T = Temporary, commonly written on spare tyres
P = Passenger car tyre
LT = Light Truck tyre
ST = Special Trailer
If you’re still uncertain as to what it all means, then the best thing to do is to seek advice from your local Tyreright expert. If you’re looking for new tyres but need to know you’re getting the right fit for your car and your driving requirements, then our team of tyre experts are available to help at any one of our stores. Don’t forget to take advantage of our free tyre health check.