A worn or damaged tyre could cause a blowout and sudden loss of control. Here’s how to spot when a tyre needs replacing.
Car tyres have a legal minimum tread depth (1.6mm). Bicycle tyres don’t. You replace them when necessary, not when a law says. In other words, when you or your local bike shop’s mechanic think they’re worn or damaged.
Wear is easy to see on tyre that has lugs, like a knobbly off-road tyre, or an incised tread pattern. If the lugs or pattern are gone or visibly fading, the tyre is worn and needs to be replaced. It’s hard to tell with a smooth, slick tyre – although some of them have inset dots or sipes. Treat these like any tread pattern: when you can’t see them, the tyre is worn.
Tyre mileage varies enormously. Heavy-duty ones with more rubber in them, such as Schwalbe Marathon Plus, might last for 10,000 miles or more. Paper-thin racing tyres might not reach four figures. A tyre on the front wheel will last longer than one on the rear, which takes more of your bodyweight and transmits drive. Tyres kept the right inflation pressure should last longer; overly soft ones are more likely to suffer punctures and sidewall damage.
The tread is so worn that you can see the threads of the tyre casing underneath. Replace the tyre immediately. You’re likely to suffer more punctures than usual before you get to this point, as there’s so little rubber left.
Small nicks and cuts
Small nicks or cuts in the tread – caused by that thorn you pulled out of your flat tyre, perhaps – are seldom anything to worry about. You can repair them with a small blob of superglue. (Flex the tyre to expose the nick, apply glue, then let the tyre return to its normal shape.) Sticky threads called tyre plugs will seal holes up to 2-3mm size in tubeless tyres.
Holes and tears
Bigger holes or tears (e.g. that you could force a pencil through) can be temporarily repaired with a ‘tyre boot’ if the tyre has an innertube. The ‘boot’ is any piece of tough, flexible material that can be placed between the tube and tyre, held in place by the tyre beads. This is a get-you-home repair. The tyre is ready for the bin.
The tyre casing has failed and the innertube is starting to press out through the sidewall – a bit like a hernia! Replace immediately.
The curved shape of the tyre, generally the rear, will gradually flatten where the central section wears on the road. Keep an eye on it: it may become threadbare soon. You can check by removing the tyre from the wheel and feeling the tread thickness with thumb and forefinger. A flat spot in one place only is caused by skidding, and the tyre won’t roll as well. Check for other damage.
If it’s just surface cracking of the rubber and not deep or extensive, the tyre will hold up for a long time yet. If the casing underneath is visible or the crack is wide, replace the tyre. Ditto if it bulges at this point. Treat sidewall abrasion similarly. If it’s just a scuff, it’s fine; if the casing threads are damaged, replace.
Tyre bead separating from sidewall
If the metal or synthetic bead at the edge is tearing away from the tyre, bin it.
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