Tyre numbers & markings explained

Tyre numbers & markings explained

Man checks tyre sizes

While many will rely on their mechanic to handle all issues regarding their vehicle’s tyres, it can be quite useful to at least have a good overview of what all those numbers on the side mean.

Looking on the sidewall of a tyre, you may see an assortment of both numbers and letters that mean absolutely nothing to you – however, these are all regarding the tyre’s size, among other things.

For those stumped by these figures on your car’s rubber, and wish to know what all this information means, then read on.

Tyre Size Explained

If you’re wanting to understand how to read tyre sizes, it’s possibly not as complicated as you may think it to be.

Reading the sidewall of a tyre, it’s likely that you’ll see something such as the following:

225 / 40 R19 93 Y

  • Tyre Width

So the first number we start with is the tyre’s width; in this instance of a tyre for a BMW 3-Series, the width is 225mm (millimetres). The tyre’s width is the part of the rubber that is in contact with the road.

  • Tyre Aspect Ratio

The second marking we come to effectively represents the thickness of the tyre wall – you may also see this referred to as the tyre’s profile – and is a percentage of the width. In our example, we have a tyre aspect ratio of 40, meaning that the tyre height is equal to 40% of the tyre’s width.

  • Tyre Diameter

While some may think the ‘R’ stands for rim, it’s actually in reference to the tyre’s construction. It is highly unlikely you’ll see anything else other than R on your car’s tyres, which stands for ‘radial’.

The number, meanwhile, refers to the inner diameter of the tyre where the wheel itself sits, and will be the same size as your alloys. In our example, the inner diameter is 19 inches.

  • Maximum Tyre Weight

The final main number on your tyre’s sidewall represents the load rating of the tyre, and is in kilograms (KG). For our tyre here, it can have a maximum load of 93 kg when inflated to the proper levels.

  • Tyre Speed Rating

For any track users, this can be quite an important marking, as it is in reference to the maximum speed the tyre can handle when inflated accordingly and under load. The letters you see can vary from Q to Y – in our example we have Y, which means the tyre can handle speeds of up to 186 mph, so not too bad at all.

How to read other tyre markings

You’ll find additional sets of numbers and letters on your car’s tyres that also have their own set of meanings.

Date of Manufacture – There should be four digits found beyond the above; the first two refer to the week of the year the tyres were made, while the two that follow represent the year of manufacture. 

For example, if you saw ‘4023’, this would mean that the tyre was made in the 40th week of 2023.

Run Flat Tyres – If your tyres are run flats, then you’ll be able to find this out by seeing if the letters ‘RFT’ are on the sidewall. 

However, you may see variations of this depending on the manufacturer, so also look out for: ROF; EMT; RFT; ZP; SSR; or DSST.

Reinforced Tyres – It might be that you’re driving a vehicle that has an extra bit of weight about it, and so reinforced tyres may be required. 

To see if your wheels are already graced with reinforced rubber, you’ll probably see the letters ‘REF’, but also look out for: XL; EXL; RF; REINF; or RFD.

Homologation – Many performance cars these days have tyres especially made for them. 

If this is the case, you may see reference to this, though how so can depend on the car – examples include: a star symbol (BMW/MINI); AO (Audi); n0, n1 or n2 (Porsche); or MO (Mercedes).