Learn the Tyre and Wheel Glossary
At Tyre King we know that not everyone is a tyre expert and that buying tyres can involve a lot of jargon. We aim to make buying tyres as simple and straightforward as possible and that is why we’ve created this easy to use glossary of terms.
Alternatively, please call one of our tyre experts on 0800 1 600 600 who would be more than happy to help with any queries you may have.
If there is any jargon you need clarified and is not listed in our glossary, please let us know and one of our tyre experts will endeavor to translate it for you.
Learn the Tyre Marking
The markings on the tyre sidewall are shorthand for a veritable wealth of information. The tyre model name is present and correct, obviously, but that’s just the start. There’s also a sequence of numbers detailing the load index, speed rating, tyre size, construction, and much more.
1. Tyre width
The first number to appear in the sequence is “225.” This number is the nominal width of the tyre (in millimeters) from one sidewall to the other.
2. Aspect ratio
Following the slash, the next number in the sequence is “45.” This number is the tyre’s aspect ratio – essentially the height of the tyre’s profile outward from the rim represented as a percentage of the tyre’s width. We calculate this number by dividing the tyre’s section height by the tyre’s section width. So, if a tyre has an aspect ratio of 45, that means the tyre’s height is 45% of its width.
Next in our series of tyre markings is a letter instead of a number. This letter indicates the type of construction used within the casing of the tyre, which in our example is “R” for Radial construction. Other examples are “B” for Bias-ply or “D” for Diagonal construction.
Radial tyres are the most common tyres on the road today. They’re called radial because the tyre’s internal ply cords are orientated in a radial direction, from one bead over to the other, at right angles to the direction of the tyre’s rotation.
4. Rim diameter
The number “18” in our example represents the diameter of the wheel rim in inches.
5. Load Index
The number after the rim diameter represents the load index. In our example, “95” is a code for the maximum load a tyre can support when fully inflated. Passenger tyres have load indices spanning from 75 to 105, where each numeric value corresponds to a specific load capacity. The carrying capacity for each value is described in a load index chart in your vehicle or tyre documentation.
6. Speed rating
Last in our sequence, we come to the speed rating. Letters ranging from A to Z represent the speed rating. Each letter denotes the maximum speed a tyre can sustain under its recommended load capacity. In our example, “H” is equivalent to a maximum speed of 209 kph (130 mph). Even though a tyre is capable of performing at this speed, drivers should not exceed legal speed limits.
7-12. Additional markings
After this sequence of information, other letters and symbols may also be present on the sidewall.
In our example, they denote the following:
|7||Self-Supporting Run-flat tyre|
|8||Mercedes Original Equipment key|
|9||Suitable for mud and snow conditions|
Compliant with US Department of Transportation motor vehicle safety standards
|11||Week of manufacture|
|12||Year of manufacture|
Tyre and Wheel Glossary
Tyres and wheels are things that seem fairly simple — but once you start peeling back the layers you realize they’re actually quite complicated. In an effort to demystify the world of tyres and wheels, with its confusing terminology, we present to you the tyre and wheel Glossary.
This is essentially the volume of air inside the tyre, it can be measured in either pounds per square inch PSI or Bar. Having the correct pressure for tyres is a key factor in Tyre Safety and can usually be found in the Vehicle handbook as well as the fuel cap flap.
This is essentially the correct vertical alignment of the tyres. Generally describes the checks and corrects made to the suspension and steering systems of the vehicle to ensure compliance with the manufacturers recommendations
Alloy wheels differ from normal Steel wheels because of their lighter weight, which improves the steering and the speed of the car. Alloy wheels are also better heat conductors than steel wheels, improving heat dissipation from the brakes, which reduces the chance of brake failure in more demanding driving conditions
All Season Tyres
Tyres designed to be used in all weathers all year round
The vehicle rides on a layer/film of water above the road surface and not the road itself. This causes traction loss and loss of control. Vehicle often can feel unresponsive and the back of the vehicle may weave or wobble. If this occurs, , put on your Hazard warning lights, avoid braking or accelerating, depress the clutch, keep a strong firm grip of the steering wheel, steer where you want to go (into the skid) and try not to stay calm.
(also referred to as Profile) Expression of a tyres height as a percentage of its section width, for example if the width was 300mm and the height was 150mm the aspect ratio would be 50%.