What do all the Numbers and Letters mean on the side of your Tyres?

You will find lots of numbers on the sides of your tyres, if these are too worn out to read then I would be concerned as to whether your treads are road worthing and within legal limits! But thats a whole new topic we will cover another day!

So the Numbers and Letters on the Side of your Tyre, are often refered to as your Tyre Size but in actual fact give you a lot more information.

You will find these numbers/letters on the sidewall of your current tyre.  The most common tyre size in the UK is 205/55R16 but there are many variations, so its very important to check your existing tyre or check your vehicle handbook to ensure the right tyre size has been installed.


Tyre Width:  The 1st three digits are the tyres width so in our example the Tyre width will be 225mm across the thread from the sidewall to sidewall.

Aspect Ratio:  The 4th and 5th digits of the tyre code that immediately follow the tyre width are the Aspect Ratio or the Profile Height of the tyre sidewall , it is expressed as a percentage of the tyre width.  So an aspect ratio of 55 as per our example means that the profile height of the tyre is 55% of its width.

Radial : Radial Tyres are marked with the Letter R.  Radial Tyres are constructed with the cord plies positioned at a 90 degree angle to the direction of travel to give the tyre additional strength.  Almost every new tyre manufactured today is a radial tyre.

Wheel Diameter:  The next 2 digits represent the size of the wheel rim that the tyre can be fitted to.  It is also the diameter of the tyre from bead to bead. So a tyre marked 16 will fit on a 16-inch wheel rim.

Speed Ratings: Tyres are marked with a letter of the Alphabet at the end of the tyre size code which indicates the maximum speed capability of the tyre. Tyres receive a speed rating based on a series of tests which measure the tyres capability to handle a set speed for a prolonged period of time.  Our example above is a V which has Max speed of 149mph. If your unsure of what speed rating you need, be sure to check you vehicle handbook. Choosing a lower speed rating than that recommended for your vehicle manufacturer could potentially invalidate your insurance.

Load Index:  You will see the no.s  91 on our example tyre these are where you will find the Load Index, this is the maximum weight capability for the tyre.  The load index is a numerical code and each code has a different maximum load for example 91 has a max load of 615kg.

That is the basics of the numbers and letters on the side of a tyre, as you will now know there are many variations on the market and you will find other numbers on them also, but we will leave you with that information for now.