Tyres: A guide for drivers

Car tyres

A guide to choosing and looking after car tyres, with information on tyre pressure, checking legal limits, tyre sizes, remoulds, winter tyres and more.

It's easy to underestimate the importance of your car's tyres.

For many people, they're a fit-and-forget item; in day-to-day motoring, they're just there, doing their job, one less thing to worry about.

But they are your car's only contact with the road, and that's a heck of an important job.

So perhaps you might want to give them a little more thought…

Tyre pressure

It's very, very important to maintain the correct air pressure in your tyres. If you don't know what this should be, it's pretty easy to find out - it'll be in the car's owner's manual.

If you don't have the manual, a sticker displaying the pressures can often be found inside the fuel filler cap, in the driver's door shut or in the glovebox.Car

Failing all that, ask your local dealer or tyre fitter, or search online for a tyre pressure chart.

There are even smartphone apps available that can tell you the correct tyre pressure by simply entering your vehicle's registration number.

It's important that you check the pressure regularly. Just how regularly will depend on your vehicle and the use you put it to, but at least once a month could, perhaps, be a good rule of thumb.

Getting the right tyre pressure is important because air reacts to heat - the friction of driving around heats up the air inside the tyre and there are various rates of expansion and contraction.

If you suffer a blow-out, don't brake harshly unless you have to - grip the wheel, hold the car in as straight a line as you can and let it lose speed gradually

The manufacturer has worked out what pressure needs to be maintained in order to stop the tyre exploding, which it can do if it's under- or over-inflated.

And if you have a blow-out at speed, you could be in real trouble.

Keeping your tyres inflated outside the recommended limits can also negatively impact on wear, performance and fuel consumption.

It's also worth bearing in mind that manufacturers recommend a slightly higher pressure if you're towing, or if the car is heavily laden - say, with five people and a bootful of luggage.Fuel cost calculator

Again, refer to their guidelines.

You can top up your tyres at most petrol stations - some have free machines, some require a coin or token - or just do it at home with a footpump and tyre pressure gauge. It's easy.

Tyre tread and wear

It's very important to ensure that your tyres are in good condition, and there are a number of things that you need to look out for.

The minimum UK legal limit for tyre tread is 1.6mm of depth across 75% of the tyre

Firstly, tread wear: in essence, your tyres are at their best when they're brand new, and gradually get less and less good as the tread wears away.

Manufacturers fit wear indicators to check the tyre tread depth so that you know when you've reached the minimum UK legal limit (which is 1.6mm of depth across 75% of the tyre).

If you look into the main groove of your tyres you'll see these indicators moulded in. If the tread surface has worn down to the same level as these indicators, the tyre needs to be replaced.

For added peace of mind, for a small price you can purchase a simple-to-use tread depth gauge. When you use this, make sure you're parked on a flat surface in a safe location, and check in several different places on the tyre in case of uneven wear.

Remember, though, that the minimum tyre tread depth set by regulations is not a guarantee of safety or performance, and that stopping distances and grip will be worse on worn rubber than with a newer tyre.

Damage is something else to look out for. If you've hit the kerb with your wheel while parking - don't be embarrassed, it happens - it's possible that you could have gouged a chunk out of the sidewall. This could lead to a rim leak, and a dangerous loss of pressure.

It's also worth remembering that the condition of your wheels is important to the health of your tyres. Thudding into a particularly nasty pothole, for example, can warp the rim and cause a slow puncture or rim leak.

These are also some of the ways to knock out your wheel balancing, so you may need to check the wheel alignment.What to do if you break down

Be sure to also keep an eye on the rolling area of the tyre (the bit in contact with the road) for nails, screws, bits of glass or anything else that could have caused a puncture.

These often stay there for some time, keeping the pressure in. But when such things eventually pop out of the tyre you'll soon be left with a flat - which isn't really very sporting…

Being made of rubber, tyres do perish with age. If they look crazed or crumbly, that's not a risk worth taking. Replacing them would be best.

Tyre sizes and labelling

The dimensions of your tyre are written on the sidewall, and are an intriguing mix of imperial and metric units.

Let's say your tyres are labelled '195/45 R15' - this means that they are 195mm wide, the height of the sidewall is 45% of the tyre's width, they're radials, and they fit a wheel that's 15" in diameter.

If you alter the rolling radius - the radius of the wheel and tyre combined - you might knock out the calibration of your speedometer

In some cases you may find that you have a few more letters and numbers. For example, we can expand that label to read 'P 195/45 R15 82H'.

The P at the start refers to the type of vehicle ('P' for passenger vehicle, 'LT' for light truck, 'T' for temporary/spare), the 82 is a load rating (see more information on this on the Blackcircles.com website), and the H is a tyre speed rating (S is for up to 112mph, H for up to 130mph, V for up to 150mph, Z for 150mph+).

This is all detail that you don't necessarily need to know, but it's helpful to be clued up when you're shopping for tyres.

You can, of course, deviate from the manufacturer's recommended tyre sizes - a wider tyre can offer more grip, a shallower sidewall can offer a firmer ride, and so forth.

Do bear in mind, though, that if you alter the rolling radius - the radius of the wheel and tyre combined - you might knock out the calibration of your speedometer and be driving faster or slower than you think you are. If you're not sure, consult a dealer or tyre fitter.

Winter tyres

Winter tyres aren't really a big thing in the UK, but perhaps they should be. In Germany they're a legal requirement, but the culture of tyre rotation barely exists over here.

Winter tyres may be an additional hassle, but they're definitely worth considering

Dedicated tyres for wintry conditions can offer improvements in braking and traction of up to 50% on snow and ice, which is not be sniffed at, and they also offer huge benefits when driving in rain.

Winter tyres are made of a more silica-rich compound than regular tyres so that they're softer.

Also, the tread blocks have more of those little slits (which are called 'sipes', fact fans), which is how they find the extra grip.

Now, you may baulk at the idea of spending an extra few hundred quid on a set of tyres for the winter, which you then have to store somewhere over the summer when you've swapped back to your regular rubber, but it's definitely something to think about.

After all, in slippery conditions it's not just your own lack of grip you have to worry about - being able to take evasive action when someone skids into your path could steer you clear of bigger bills, or tragedy.

Mis-matching tyres

Your car's chassis is largely symmetrical. So if you replace something on one side that has an equal counterpart on the other (like a shock absorber, say) then you should replace them in pairs.How to cut the cost of breakdown cover

This is also true of tyres.

It is legal to have tyres of different brands and with different tread patterns on the same axle. But why would you risk it?

There are so many variables in terms of construct, grip rate, wear rate and so on that the likelihood of braking in a straight line in an emergency is rather diminished.

You may find that one side grips a lot better in the wet too.

Tyre brands and remoulds

You don't have to spend a fortune to get good tyres. But it does pay to be wary of very cheap ones.

If you're not hugely confident in the world of tyre buying, a good rule of thumb could be to just buy a brand you've heard of.

A 2010 What Car? test compared the performance of Michelin, Goodyear, Continental, Arrowspeed, Ovation and Sunew tyres.

The latter three, the budget tyre options, took an average of 14m longer to stop from 70mph in the wet. That's the length of an articulated lorry!

Also, beware of remoulds. These are made from the shell of old, used tyres, with a new tread grafted onto the skin.

While some argue that they're a sound ecological choice, many more argue that they're potentially dangerous - they generally have poorer grip and higher wear rates and, in an emergency stop situation, the new tread can simply shear off the old shell. Not worth the risk.

How can you tell if you're looking at remoulds? They have to have 'remould' written on the sidewall.

By Daniel Bevis