We all know that tyres don’t last for ever but exactly when do they need replacing? Here’s how to tell when the time has come for a new pair.
There are essentially five parts to a clincher tyre (standard tyres that use inner tubes, held in place by a bead that hooks to the wheel rim, as opposed to tubulars that are bonded to the wheel):
Casing The supple body of the tyre, made of nylon (usually) in various numbers of threads per inch (TPI), that’s covered in rubber.
Protection layer Manufacturers sometimes use various different types of material underneath the tread to provide resistance against punctures.
Tread The compound that comes into contact with the ground.
Bead The bit around the edge that secures the tyre to the wheel rim. These are made from wire or foldable Kevlar.
Anti-chafing strip The reinforcement that protects the bead.
Most road bike tyres will go through their lives without experiencing too much in the way of trauma, but you might hit a pothole, a big stone, or some other obstacle that causes damage to the structure, or something might ping up from the road surface.
Check your tyres carefully if anything like this happens.
“A casing breach of any size in the sidewall/ 2mm under the tread would usually render a tyre disabled and ready for replacement,” says Shelley Childs of Cambrian Tyres, the company that distributes Continental bike tyres in the UK.
“If you hit a pothole and feel the wheel rim has made contact with the road surface, then there is a chance that the tyre sidewall (casing) has been breached, even if there is no air loss of the inner tube. Stop and check.
“Also, if you ride over something that causes an obvious bump or jerk to the handling of the bike, your tyre may have been damaged, even if you don’t suffer a puncture. Again, stop and check just to be safe.
“If you do see a tear anywhere on the exposed surface of the tyre (tread or sidewall), inspect it thoroughly and try to see if the inner tube is visible. If so, the tyre is unsafe. If not, then the casing should still be intact and you can ride on, but get the tyre checked by your local dealer just to be sure.”
Check the wheel too.
“If the tyre/tube survives a pothole smash then it’s essential that after you’ve checked the tyres you should also check your rims to make sure that their structure hasn't been compromised,” says Schwalbe's Dave Taylor. “A dented rim or displaced spoke can cause unwanted friction for tyre and tube which could lead to a puncture on a later ride.”
Tread wear indicators
Most often, though, tyres simply wear out gradually with use due to contact with the road.
Some tyres come with tread wear indicators that tell you when it’s time for a replacement.
Continental road tyres, for example, now have two small ‘tap-holes’ in the central area of the tread. These are designed to disappear as the tyre nears the end of its serviceable life. Once the holes are gone it’s time to bin the tyre, no matter how tempting it is to try to wring a bit more life out of them.
A small triangle and the letters TWI on the sidewall show you where the tread wear indicator should be.
Although it's getting worn, the tread wear indicators on this tyre (above) are still visible.
Other manufacturers use their own tread wear indicators. This one (above), for example, is on a Giant tyre.
If you’ve skidded your bike it could be that the tread wear indicators are still intact but you’ve worn through the tread in another area. You need to change your tyre in this situation.
What if your tyres don’t have tread wear indicators?
“A tyre will change its shape slightly once it has worn out,” says Shelley Childs. “As well as affecting the handling of the bike slightly, it will no longer look round in the cross section [as above], it will look more square, as the tread area has worn significantly.
“If your tyre had a tread pattern, this will have disappeared and in extreme cases, you may even see the casing material showing through.“
Dave Taylor says, “When the puncture protection belt or the carcass threads can be seen through the tread the tyre has reached its wear limit and must be replaced. As puncture resistance also depends on the thickness of the tread layer, it may be useful to replace the tyre sooner.”
If your tyres don’t have tread wear indicators, repeatedly getting flats from small stones and pieces of glass is an indication that the tread could have worn thin and it’s time to replace your tyres.
If the protection layer or the casing is showing through, it’s definitely time for some new rubber.
A tyre’s sidewalls will sometimes fail before the tread is worn out.
“In most cases, this premature failure is due to prolonged use of the tyre with insufficient inflation pressure,” says Schwalbe. “Checking and adjusting the inflation pressure at least once a month with a pressure gauge is most important.”
The sidewalls may be damaged if a bike is left on flat tyres for a long period. If fitted on a wheel, tyres should be inflated or the wheel should be hung up for storage.
If the bead is damaged and is blown off the rim when you inflate the inner tube, you need to replace the tyre.
Don’t worry too much about the depth of the tread pattern – if there is one on your tyres – affecting performance. When we visited Continental last year, their experts told us that the tread pattern doesn’t make much difference on the road. It has a role in certain circumstances, but it doesn’t do much, unlike off-road when the tread pattern is vital in determining grip on conformable ground.
However, if the pattern is getting shallow, that could be a warning that the tread itself is wearing thin and that the tyres will soon need replacing.
Swapping front and rear tyres
Your rear tyre will invariably wear quicker than your front tyre. Some people will swap over the front and rear tyres after some use to make sure they wear out at roughly the same time, but Shelley Childs doesn’t think this is good practice.
“It is not advisable due to the change in handling characteristics of each tyre as they become worn,” he says. “A rear tyre will be square, whist a front tyre more rounded. To put a worn rear tyre on the front wheel would negatively affect the handling of your bike.”
Schwalbe's Dave Taylor isn't so opposed to the idea.
“This is really up to the individual rider and takes into account things like their own budget, riding style, riding distance, and riding surfaces," he says. "You would want fresh rubber front and rear for a gran fondo, for example, but would settle for a front and rear swap for your daily commute.”
Mat has worked for loads of bike magazines over the past 20 years, and been editor of 220 Triathlon and Cycling Plus. He's been road.cc technical editor for seven years, testing bikes, fettling the latest kit, and trying out the most up-to-the-minute clothing. We send him off around the world to get all the news from launches and shows too. He has won his category in Ironman UK 70.3 and finished on the podium in both marathons he has run. Mat is a Cambridge graduate who did a post-grad in magazine journalism, and he is a past winner of the Cycling Media Award for Specialist Online Writer.