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What do the numbers on tyre sidewalls mean?

2018-02-15 06:00

Tyre sidewall markings are like international shoe sizes: challenging at first to decipher, but easy to get excited about once you get the hang of them.

Municipal account numbers, tax numbers and your DSTV’s decoder serial number: pointless digits that only complicate your life amidst your best efforts to escape the morass of modern living.

And when it comes to your car’s footwear, there are none as irrelevant as the numbers that adorn its tyres’ sidewalls, right? Wrong. Each has a life story – you just need to know what to look for.

Let’s take a tyre size: 265/30 R20 94Y. The first six of these are geometric specifications, in this instance meaning that the tyre is 265mm wide, while the height-to-width ratio (or aspect ratio) is expressed as a percentage of the width (in this case, 30% of 265mm), and the inner diameter measures 20 inches to fit a rim of that size.

Of course, there’s more. The tyre’s load index number specifies the maximum load that can be carried at its given speed rating. These weight-per-corner carrying abilities are classified from “62” (able to carry 265kg) to “126” (1700kg). The “94” rating from our example above amounts to a 670kg carrying ability.

Now, for the fun part. Speed ratings start at “E” (70km/h) and end at “Z” (240km/h), although curiously “Y” is a higher speed rating than “Z” – 300km/h. 

Those are the speed stats, so how about some biographical information? Furthermore, the tyre’s composition is explained (usually a combination of layers of steel and polyester), its traction rating on wet surfaces (“AA” is the highest and “C” the lowest) the operating temperature range as well as the maximum allowable pressure it can be inflated to. Similarly, temperature ratings refer to the ability to withstand heat at high speeds, from “A” to “C”.

But most significantly – especially helpful when it comes to the replacement of tyres (every five years, regardless of the distance covered) – is that they tell you when they were made. However, should you use your vehicle for business or travel long distances daily, the tread on the tyre could wear out much faster and tyres would need replacing sooner.

It’s strongly advised that tyres are checked once a month. All tyres have tread indicators, but these can generally only be seen on the surface of the tyre once the tread depth has already reached its limit at about 1.6mm. Tyres should then be replaced as soon as possible.

The final four digits following the DOT number indicate the week and year of manufacture. It is expressed as a four-digit code in a week/year format, so “1214” would mean that the tyre was produced in the 12th week of 2014.

Geeky? Probably. But consider that tyres are the sole point of contact between your car and the road. And that the contact patch represented by each tyre is smaller than the size of your palm.

These round hoops are the most overlooked and underrated safety kit on the average car. They have to grip, steer, power and brake, usually without you giving them a second of thought. Considering they could save your life, isn’t it worth getting to know them a little better? 

Find the right wheels for you at AutoTrader. AutoTrader South Africa has a multitude of new and used vehicles for every possible kind of preference, and has been the leading media marketplace for the past 25 years. Whether you are looking to buy a brand-new car or are in the market for a pre-loved model, AutoTrader has over 71 000 quality cars to choose from! Visit AutoTrader today to find your dream car.

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