If you’re reading this sentence, there’s a very high probability that you drive a car or own a vehicle that has a set of tyres. Good tyres are important for several reasons, and great tyres can make the difference between stopping behind a car and crashing into one. Braking distance, terrain manoeuvrability and grip are all affected by the many facets of each tyre on your vehicle, and a fault or worn area could detrimentally affect its entire performance.
If you’re worried about whether your tyres are up to scratch, there are several things you can do. A 5-minute check goes a long way, but the markings on your tyres are also there to help! You might not even know they exist, but there are several figures and codes on the sidewall of your tyres that provide important information. We’re not making this up, go and have a look if you don’t believe us!
Knowing the size of your tyres is especially important, as you’ll need it if you want to shop around for new ones. There are plenty of tools to help you online, and Asda Tyres provide a simple number plate check to help you find your size too. However, it’s always best to be prepared.
The size is typically a sequence of numbers and letters, arranged like the following Dunlop tyre: 205/55R/15/91V. There may be slight variations on the way this is arranged, but the meaning always remains the same.
Tyre Width: The first three digits represent the width of the tyre in millimetres from sidewall to sidewall. In this case, it would be 205mm.
Aspect Ratio: The fourth and fifth digits represent the aspect ratio of the tyre. This just describes the profile height of the sidewall, which is defined as a percentage of the tyre’s width. In this case, it would be 55% of its width.
Radial: The R represents the type of tyre. Most tyres created today are radial, which implies that the cord piles are positioned against the direction of travel at a 90-degree angle. This gives it additional strength.
Wheel Diameter – The final digits represent the wheel diameter of the tyre. This just means the size of the wheel rim that the tyre should be fitted to. In this case, the tyre should fit on a 15-inch wheel rim.
With this knowledge, you can safely choose your next set of tyres. We’ve heard of people choosing the wrong tyre, or spare tyre, before. Now that you know where the size is, you shouldn’t have this problem.
The speed rating can be found at the end of the size code. It uses the following sequence of letters to determine maximum speed:
- Q: 99MPH
- R: 106MPH
- S: 112MPH
- T: 118MPH
- H: 131MPH
- V: 149MPH
- W: 168MPH
- Y: 186MPH
Tyres are thoroughly tested by extremely smart people to determine this speed rating, as it implies that the tyre can travel at this speed for an extended period of time. You’ve got to be careful with this, as a lower speed rating could invalidate your insurance if it’s incorrect. You can usually find the correct speed rating in your trusty vehicle handbook.
Look for the two digits before the speed rating to determine the load index. Each tyre is only built to handle a specific weight, and using a tyre with a lower load index – while not illegal – is not recommended. The digits range from 65-108, with our example (91) being able to hold a maximum weight of 615kg.
You’ll find all the details about your recommended load index in your vehicle handbook. If you have doubts about the load rating, always play it safe and go for a higher load rating than you feel is necessary. Tyres with a lower rating could result in safety issues and insurance invalidation, which would result in heavy costs in the event of an accident.
If a tyre has an increased load index, it may be marked as reinforced. This implies that the tyre can handle more weight, while it should also provide better stability, handling and resistance to additional forces such as acceleration and braking. They also resist damage from hitting curbs too!
However, it’s not all sunshine and rainbows. The tyres are generally noisier, bigger and result in higher fuel consumption. Driving comfort is also usually affected. There are many symbols used to display if a tyre is reinforced, but common ones include REF and REINF. XL and EXL may also be used to display that a tyre can carry extra loads.
Date of Manufacture
Tyres also include the date of manufacture, which is displayed as a series of letters and numbers. (Usually after the load index and speed rating.) It begins with the letters DOT, which simply means that it meets the safety standards set by the Department of Transport. You’ll then see 8 characters of letters and numbers, which indicate the tyre’s serial number and production facility where it was made.
After the serial number, you’ll see 4 digits. They may be shown in a small box for easier visibility. The first two digits represent the week that the tyre was made, while the latter digits represent the year that the tyre was created. For example, if you see a tyre with 1418 on it, it means that it was made during the 14th week of 2018! Easy, right?
Punctures are the bane of many drivers, so run-flat tyres were created to solve this problem. These tyres have stronger side walls which hold the weight of the vehicle for longer in the event of a puncture. (You should still replace the tyre as soon as possible, but these provide a temporary reprieve.)
Confusingly, different manufacturers have different markings for their run-flat tyres. For example, Dunlop displays DSST (Dunlop Self Supporting Technology), while Goodyear displays ROF (RunOnFlat) or EMT (Extended Mobility Technology). The markings are usually found after the date of manufacture, but it does vary depending on the brand.
Many manufacturers are increasingly creating tyres that are intended for specific vehicles. These provide performance benefits, and ideally, you should be using the intended tyres if your vehicle has them. Well-known car manufacturers, including Ford, Mercedes and Audi have their own markings for this purpose.
They’re usually quite easy to decode. For example, Audi uses A0 and Mercedes uses MO. However both BMW and Mini use the star symbol, while Porsche uses N0 to N6! Some cars just have to be different.
You can usually find out more about this from your manufacturer, and the tyres may even be in your vehicle handbook. If you purchase one of these tyres, you can guarantee that the rest of the markings will match your vehicle.