Those black round things on your car are super important, more so than you may realise, they are actually part of your braking system, suspension system and aid your power delivery, aside from there being legal requirements to adhere to in the UK, knowing your tyres, knowing there capabilities and limitations will help you not only on the road but also on the track.
In this blog we are going to cover the symbols and markings on the sidewall of your tyre and what they mean, this will help you understand the tyre you currently have on or help you decide on what you would like out of your next set of tyres. You may be surprised at the how much information is on the sidewall of tyres.
Below is an image of the basic numbers and letters you see on the sidewall of a car tyre, in this example the tyre is a 225/40 ZR 18 92Y, but what do they stand for?
Section Width (225)
The section width is the width of the tyre’s tread in millimetres. In this example the tyre is 225 mm wide.
Aspect Ration (40)
The aspect ratio is the height of the sidewalls of the tyre expressed as a percentage of the section width. In this example the height of the sidewalls is equivalent to 40% of the tyre’s width (225 mm) which is 90 mm.
Z
This is something that doesn’t always appear on tyres. The ‘Z’ indicates that the tyre can safely operate at speeds higher than 150 mph. This is in addition to its normal speed rating (see below). Your tyre will not have this ‘Z’ if it’s rated for a speed lower than 150 mph.
Radial (R)
‘R’ simply stands for ‘radial’ – indicating that this tyre has a radial (rather than cross-ply) construction. You should never mix radial and cross-ply tyres – although just about every consumer tyre you can buy nowadays is radial. With regards to the construction of the tyre you may also see additional letters such has “LT” for Light Truck & “C” for commercial, there are differences in the construction so if your vehicle came from factory with LT or C tyres, you must continue to fit LT or C constructed tyres.
Rim Diameter (18)
The rim diameter is the size of wheel that the tyre will fit onto – measured in inches. In this case, the tyre is designed to fit on an 18-inch wheel.
Load Index (92)
‘92’ refers to the tyre’s load index – which tells you how much weight it can safely carry., In order to find out the load index in kg, you need to look up the number on your tyre in a tyre load index table. The bigger the number, the higher the rating. In this example 92 is 630kg. This is really important when changing your tyres, if your car came out from factory with, for example, a 92-load rated tyre, you cannot put a tyre on that has a lower load rating than 92, it must be the same or greater.
Speed Rating (Y)
‘Y’ refers to the tyre’s speed rating – which tells you how fast the tyre can safely travel. This is very important for safety. In order to find out what your speed rating actually is, you need to look this letter up in a tyre speed rating table. In this example the Y means the maximum speed for this tyre is 186mph. When changing your tyres, if your car came out the factory with, for example, a Y speed rated tyre you cannot put a lower speed rating on, it must be Y speed rated or greater rating.
The numbers and letters will change depending on vehicle, application and size but the layout remains the same. Now we will move on to markings and symbols you may not be too familiar with.
Speed Brackets
In the Speed Rating table, the letter Y has the highest maximum speed rating at 186mph, however on some Y speed rated tyres you may see either brackets around the letter Y for example 92 (Y) or the brackets may be around both the load rating and the letter Y for example (92Y). What this means is, that Y speed rated tyre is capable of handling speeds greater than 186mph. If your car came out the factory with tyres that were Y speed rated with speed brackets then you must continue to fit tyres that are Y speed rated with Speed Brackets, not just Y speed rated.
XL & HL Tyres
XL stands for Extra Load; HL stands High Load. It means that the tyre has been reinforced to be able to carry heavier loads and will have a higher load capacity than another tyre in the same tyre dimension. Please note here that if your vehicle comes from factory with an XL or HL tyre, you should continue to fit an equivalent tyre when they need replacing.
Homologated Tyres
Homologated tyres or OE tyres are tyres that have been created in conjunction with a vehicle manufacturer to go on a specific model(s) of vehicles from that manufacturer, and the tyre sidewall will have a homologation mark put on it. The marks come in various forms, sometimes a symbol, sometimes letters, sometimes letters and numbers and sometimes a combination. For example, BMW uses a star symbol, Porsche has N0, Land Rover have LR as just some examples. Some manufacturers like Porsche have several different versions of homologation marks, they have NF0, NA0, N2, N3 and others.
The reason vehicle manufacturers do this is to make sure the tyre is going to behave to the vehicle’s requirements, in some cases it can be speed, handling, noise level, EVs it can be efficiency and there’re many other reasons. Depending on the manufacturer and the model, they want the tyre to behave a certain way, and they do this by working with a tyre manufacturer like Michelin or Continental to create homologated tyres that behave a certain way for that specific vehicle.
Run Flat Tyres
The sidewall of a tyre will tell you if you have a run flat tyre however it can be displayed in different ways depending on the manufacturer of the tyre. Not all run flats are the same, each manufacturer has their own versions of run flat technologies, and some manufacturers have multiple versions, for example Michelin has ZP (Zero Pressure) and EMT (Extended Mobility Tyre), Continental uses SSR (Self Supporting Run flat), Falken uses FEXM (Falken Extended Mobility) as just some examples.
Each manufacturer will either have ‘run flat’ written on the sidewall and/or the abbreviated letters for the specific run flat technology they have put into the tyre. The run flat technologies can differ, for example they can have stronger sidewalls to support the tyre during pressure loss or they may use a type of liquid or gel that seals the tyre when punctured.
It’s important to note that having run flat tyres doesn’t mean you can get a puncture and carry on driving forever, the run flat technologies that manufacturers put into there tyres have maximum speed limits and maximum distances that the tyre can handle when it’s punctured, and this is so that you can reach a safe place to stop to call for help or if in range to be able to get to a tyre garage close by, to then repair or replace the punctured tyre. So, it is important to know if your tyres are run flats, what type of run flat technology is in them and what the maximum speed & distance they can handle if punctured.
3PMSF Symbol
3PMSF stands for 3 Peak Mountain Snowflake, and the symbol is a 3 peak mountain with a snowflake inside it and has “M+S” next to it also. This symbol can be found on the sidewall of winter and some all-season tyres that have passed a regulated test for use in snow.
Technology Symbols
Tyre manufacturers are pushing the boundaries of what is capable from a tyre and they spend a lot of time and money into researching and developing technologies such as run flat technologies, but there’re other ones to be aware of especially with regard to the amount of noise a tyre produces, something you may not have thought of but as new cars are getting quieter the noise produced by tyres is becoming more apparent. So Tyre manufacturers are creating technologies that reduce the road noise produced by there tyres, for example Continental have ContiSilent, Bridgestone have ENLITEN and Michelin have ACOUSTIC technologies in some of their tyres. The sidewall of the tyre will have a symbol, or the technology name written on it to tell you if it has such a technology.
ECE Approval Marking
The ECE approval marking is a circle with the letter E with a small single or double digit number inside with an approval number on the right outside of the circle. This means the tyre is approved to be used on the UK roads. If a tyre does not have this marking, then you cannot legally use it on the UK public roads, it would be for off-road and/or competition use only.
Manufacture Date
You may hear people refer to DOT codes on tyres, what they mean is the date of manufacture of that tyre, that is shown within the DOT code on the tyre sidewall. The DOT code is made up of a series of numbers and letters, the last four digits of the DOT code is the week number and year that the tyre was made.
Tubeless Tyres
On the sidewall of the vast majority of modern tyres it will say Tubeless, this simply means the tyre does not have an innertube inside it. However older classic cars may have come out from factory with tyres that require inner tubes, so for those that either have or are looking to get a classic car, it’s important that you are aware to check if the car requires inner tubes.
More Info
Hopefully this blog has helped you when it comes to understanding the sidewall of your tyre, of course if you are still unsure and need assistance we have a dedicated tyre sales team that are more than happy to assist you with anything tyre related. This is not the only blog we have regarding tyres, we have other tyre related blogs that you may find interesting and helpful, we have put together a list below for you.