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Tyres for Dummies

Tyre durability and performance are really important factors in how a car handles and steers.  Many of us are happy to just jump inside our cars, turn the key and drive away with little thought given to tyre performance, science and design.  On the side of your tyre are a whole lot of numbers that mean lots of different things.  Let’s take a look at the most important ones.

When it comes to a tyre, size really is significant.  Ultimately, you want the right size tyre for your car.  The car’s designer engineers have tested and proven the right size tyre for you particular car’s design.  So getting it wrong here really makes a huge difference to the way your car handles safely.  What do the numbers mean?  Using an example of a 235/45/17 tyre, these numbers tell us that the tyre’s width is 235 mm.  The next number to consider is 45; and this figure is a percentage figure that tells us the height of the tyre wall.  So the height of the tyre wall is 45% of the width of the tyre.  The width of the tyre in this example is 235 mm, so the height of the tyre’s side wall is 45% of 235 mm which equates to 105.75 mm.

Take a look at your car’s tyres and you’ll see there is plenty of other information printed on the sidewall.   Some of the other figures you’ll find provide other important information.  The load rating, the speed rating and the type of tyre can be found printed on the sidewall of the tyre.  An example might be 94Q M+S.  This tells us that 94 is the load rating for the tyre which stands for 670 kg.  Any weight on the tyre that is less than this means that the tyre will safely perform; exceeding this weight and it becomes dangerous.  There is a load rating table that you can refer to in order to make sure that you have the right tyre for your car.

Now, the Q stands for the speed rating of the tyre, and in this case Q means that the tyre has been designed to safely perform at speeds up to 160 km/h.  Over this speed and the tyre becomes unpredictable and unsafe.  The higher the letter, the faster you can go, so a tyre with a Z speed rating will be commonly found on supercars like Porsches and Ferraris.

The letters M and S stands for a “Mud and Snow “ tyre design which is a pretty standard all-season tyre – common for many vehicles.

You’ll also find the maximum tyre pressure rating.  It might be “Max 44 psi”.  This stands for the maximum amount of pressure that the tyre can handle without exploding or at least becoming dangerous.  This is, however, not the tyre pressure you should set your tyre to for everyday driving.  I does depend upon the manufacturers specifications.  Generally most cars have their tyres set between 26 and 36 psi, but it’s always best to check the manufactures manual.  Trucks and trailers have very different requirements for tyre pressures.

You’ll also find the brand of tyre printed on the sidewall.  Michelin, Goodyear and Bridgestone are some common reliable brands.

Amazingly more than 200 different materials are used in the construction of a tyre, and you’ll find materials like carbon black, silicon, sulphur, plastersizers (which increase the plasticity or viscosity of a material), vulcanizing agents, steel or even Kevlar.  These different raw materials are used to make a wide variety of components that are used in the manufacturing of a tyre – each of which give the tyre strength, durability and flexibility.

If you’re a driver who wants the best performance and handling from your machine, doing a bit of homework on the brands and types of tyres available, and there reputation in the wet and dry, will help you to make the best informed decision when it comes time to get a new set of tyres put on your car.  Some of the better known tyre brands are: Michelin, Bob Jane, Bridgestone, Dunlop, Goodyear, Hankook, Kumho, Pirelli, Continental and Yokohama.

Most of all, drive safe out there!


  1. John says:

    Another very important number is the date code. Tyres typically are only guaranteed for five years. After this date, they can be unpredictable, and a cause of blowout at highway speeds, and tyre companies may not accept a claim for damage due to failure. There are 4 numbers, and a code of 1816 means that the tyre was manufactured in the 18th week of 2016. very few workshops even know this, and never looked at for roadworthy certificates. The code can be found as an embossed oval near the rim, normally only on one side. John

    January 24th, 2017 at 11:38 am