Car care: How to check and look after your tyres

Posted by mustard.co.uk on August 26th, 2020

Tyres. They’re the most significant, hardest working part of your car, yet you probably only give them a thought when something’s gone wrong. With recent cars even including the ability to check pressures (or warn of deflation) from the dashboard, you might even have forgotten your car has tyres at all.

There’s a lot more to tyres than just making sure they’ve got air in, though; and their condition can make the difference between a relaxed drive or feeling anxious in poor weather. Neglected tyres are dangerous, so here’s how to keep your car’s wheels turning in the safest, most efficient manner possible.

If you use your car regularly, then the chances are you’ll notice problems, but not wear. If you only drive occasionally, neglected tyres can degrade and be unsafe when you most need your car. Either way, we recommend weekly checks at best, and no more than a month without inspecting your tyres for wear and damage. And if you’re concerned about anything, bring it up at your next scheduled car service or visit a dedicated tyre shop.

What’s the legal minimum tread depth for car tyres?

When buying a used car, or maintaining your own, tyre tread depth is the number one consideration. In fact it should probably be lower down the list of worries than it is for most modern cars purely because it’s so obvious, but it’s the quickest way to get a fine, and the easiest way to end up in an accident if you let your tyres wear out.

The legal minimum tread depth is 1.6mm in the UK.

How to check tyre tread

You can measure tread depth with a coin. This used to be a 10p referenced against the dots, but now you use a 20p – if you can see all of the 20p writing, the tread is below the minimum level.

Tyre condition is about more than just treadwear – you also need to have no splits, bulges or cracks in the sidewall and no cuts or exposed cord anywhere (even if the tyre has plenty of tread). Remember that the tyre has two sides, too – put gloves on and feel around the back of the wheel, or turn the steering to view both sides.

How to check tyre pressures

Correct inflation is vital for safety and economy. Most cars have a range of tyre pressures easily referenced, either inside the fuel filler flap or on the door frame, but if it doubt you can look them up online. In the absence of any information at all, inflating to around 32 to 35 P.S.I is a safe range for most cars; high performance, off-road and unusually light or heavy vehicles may have more variation.

It is important to have the same pressure side-to-side, but you can have different pressures front to rear. Tyre pressures can also be increased for sustained high-speed or fully-laden vehicles; if you have forgotten to check this and your tyres are otherwise correctly inflated, the car should be safe, but may be less efficient or comfortable.

Understanding your tyre specifications

Fitments for tyres have become, largely, standardised. This makes it easy to get tyres anywhere in the world, and to ensure different brands are at least vaguely compatible, though it’s not a good idea to have different types of tyre on the same axle (opposite each other).

Tyre sizes are specified as in inner diameter, a width, and a profile; the width and profile come first in the form of mm and ratio in percent. For example, an older small car might have 165/55 or 165mm wide, 55% deep, a high-performance car might have 235/40. The next measurement in the name is the diameter of the tyre; this is in inches, and most modern cars have sizes from 14-inches to 22-inches. Older cars could have wheels as small as 10 inches in diameter – that’s smaller than a vinyl record!

What do the numbers on your tyre mean?

With the three main measurements on your tyre – for example 235/40 and 17 – you’ll also notice the first letter. Nearly all tyres you find now are radial, so 235/40 R 17 is how you know what size of tyre you need.

There are two more crucial measurements. After the diameter, you get a load index, which specifies how firm the sidewalls of the tyre are, and how much weight they can carry. Manufacturers will give a range of ratings here; if you prefer a softer ride, you can chose the lower number, if you regularly have a fully-laden car or are towing, you may find the higher rating feels more secure.

Some types of tyres have additional reinforcement; if your manufacturer specified it for your make and model of car, stick with it. The stability control, any active suspension, and the overall feel and predictability of the car have all been designed around that tyre’s behaviour.

The most important rating of all for high performance cars is the final letter. Ranging from N to Y, this covers sustained speeds from 87mph to 186mph. Using the correct tyre for your car’s performance is vital, and if you’re involved in an accident where speed was a factor even brand-new, perfect tyres could invalidate your claim, or the claims against you, if they’re the incorrect rating for your car.

Except in extreme cases, there’s very little money to be saved when buying tyres of a lower speed rating. Don’t cut corners here. Fitting the wrong tyres for your car could even invalidate your insurance.

Matching tyres: Are they important?

Historically you could get two major differences in tyre – crossply and radial – and the consequences of mixing them could be fatal. These days tyres adhere to the same advanced construction techniques, but they still have many differences in performance. You should always match tyres side-to-side; front to rear is less important, but for the most effective performance of car safety systems, all-wheel drive and stability control keeping the same type of tyre all-round is the best course of action.

You should ensure you have the same load index and speed rating at the very least. If your current tyres are handed – directional – then you should replace the opposite side with the same kind, or replace both tyres ideally.

Some four-wheel drive cars require tyres to be changed in sets of four so they wear evenly. A mismatched tyre can overload the all-wheel drive technology and cause premature failure, though this is becoming less of a factor with the latest systems.

Extra features: weather, rims and runflats

Around the standard specifications of tyre, there are a few other common features to watch out for. The most obvious is ‘seasonal’ tyres. Winter tyres are more effective below 7 degrees centigrade, though they may have lower speed ratings than your manufacturer recommends they’re the one time it’s okay to fit something different.

Summer tyres are the opposite, optimised for grip in dry weather but prone to offering little extra when the temperature drops. If you’ve got winter tyres on in summer, they may wear faster and produce more road noise (in the UK, studded tyres aren’t legal on the highway – but the compounds are noisier too), and if you’ve got summer tyres in winter, you may find snow isn’t dispersed as easily from the tread, the compound can become greasy or inflexible to touch, and your cornering will be less secure.

Naturally there’s a compromise available, and for most cars ‘all-season’ tyres are fine for all but the most extreme weather conditions in Britain. Off-road vehicles are usually equipped with mud & snow tyres designed to operate well year-round, but faster SUVs often come with more purposeful compounds and should be top of the list for swapping summer and winter tyres to get the most out of that all-wheel-drive security.

If you have larger wheels on your car with low-profile tyres, the risk of ‘kerbing’ – scraping the rim of the wheel on kerbs, edges of potholes or rocks – is increased. To mitigate that, many premium tyres include a raised, robust lip, which will make noise and push up to prevent gentle damage from kerbs. More determined efforts will still lose the wheel’s shine, though!

Finally, the most useful development for many drivers is the appearance of run-flat tyres as standard fit on many more vehicles. Once a specialist technology for armoured cars and specialist vehicles, these reinforced- tyres will protect the wheel and give a small amount of tread for slow-progress over a longer distance, or retain stability in a blowout, making the lack of spare wheels and toolkits in modern cars less of an issue.

They require special rims and aren’t a magic solution – some damage can still render them dangerous – and they’re often less refined in terms of noise and comfort. If you’re afraid of being stranded by a flat tyre, though, they are the most appealing option you’ll find on a modern car.

As long as they meet the specifications for your car, the brand and type of tyre you have is unlikely to affect your insurance premium or claim. However, you will want to inform your insurers if you fit upgraded or aftermarket wheels. Check with your insurer before fitting winter tyres, too – some will charge an an additional premium, despite the safety benefits, but not informing them of the change could invalidate your cover. Conversely, some insurance policies may support this common sense, and also offer cover for a second set of winter tyres and wheels when they’re not installed on your car, if not covered by your home contents policy.

As always, it’s best to be honest and accurate when getting your insurance quotes, making it easier to find the best insurance for you.