- Broken glass and flints
- Thorns and nails
- Pinch punctures
- Leaky valve
- Things which don’t help, much
There are six main causes for flat tyres, and I’ve suffered all of them. There are ways to reduce the effects for each. Fixing a puncture is by far the most tedious work on a bike, so it is worthwhile doing everything you can to avoid it. Puncture patching will be covered in another Newsletter.
- The main things to do are
- Pump your tyres up hard.
- Replace the tyre, as well as fix the puncture, if its tread is worn smooth in the centre.
- Use thick tyres – the more tread the better.
- Ride out of the gutter.
Broken glass and flints
Are much worse in wet weather, especially when it hasn’t rained for a while so debris has not been washed away. Little slivers of broken glass are washed out of cracks in the road when it rains, then they stick easily to wet tyres and get several goes at embedding themselves. Water even lubricates the sharp edge as it cuts its way in. It helps to ride where there isn’t much broken glass – well away from the gutter, where car tyres have ground it up and pushed it away. Some so-called bike paths collect lots of glass after a Saturday night, and are worth avoiding while it’s fresh.
A few American states have passed laws insisting on returnable bottles. Cyclists there report a sharp reduction in punctures.
Some models of tyre are better than others: I’ve had very good results from Continental Top-Touring, but these are expensive and wear quickly at the sidewall unless used at their highest allowed pressure. Different tyres seem to suit different people, though: Dave Earl swears by Michelin World Tour, which also resist punctures fairly well, and wear the tread rather than the sidewall.
Thorns and nails
Apart from not riding over these, there’s not much you can do. The twigs left on the road where a farmer’s cut her hedge are probably full of thorns: if the road is strewn with them, it’s quicker to walk.
Sharp-edged potholes and similar nasty bumps can cause these. They often produce two small holes in the inner tube where it was squeezed between rim and road, giving these holes another name – snake bites.
The best prevention is to pump up your tyres to their limit, or yours if you have an ordinary pump. A pressure gauge (£1 to £10, depending on how accurate, how heavy, and what kind of valve it fits) can help. Until you have used one, you won’t know how your tyres look and feel at the maker’s pressure marked on the side. A track pump (£25 to £35) includes a gauge and makes much lighter work of a regular check (every fortnight or so). Pick out glass before you pump up a soft tyre to high pressure, too.
Don’t use a garage air line. Although cycle tyres use much higher pressures than car tyres, they don’t need very much air. It is all too easy to have a tyre explode in your face with one push of the garage’s control lever!
If you have a single puncture that is in the inside of the inner tube, not lined up with any scar in the tyre, it may be caused by a sharp spoke, a rough or cracked part of the rim, or the rim tape.
If it’s the end of a spoke, file that down, or get your bike shop to do it.
A cracked rim needs urgent replacement, usually of the whole wheel.
Rim tape covers the spoke ends and protects the inner tube from the metal spokes, nipples and rim. If it’s causing problems, replace it (Velox make the best, which lasts for ever and costs about £1.50 per wheel.)
Presta valves (the ones with the little locking screw) hardly ever leak, but can’t be fixed if they do. You’ll need a new inner tube.
Schräder (car type) valves sometimes leak. A special tool can be used to service them, including replacing the valve core. The tool and cores come from car parts shops.
Woods valves, now quite rare, sometimes leak when their little rubber tube is damaged or rots. This is easy to replace, if you can find any shop which still sells them; or the whole valve is also replaceable. Inner tubes with Schräder valves usually fit wheels designed for Woods valves, but you may need an adapter for your pump if you do this.
Old, thin, worn tyres, a hot day, and hard braking can combine to make a surprisingly loud bang. Replace your tyres before they get to this stage! By the time the tread or knobbles have worn smooth, your tyre is tired. If your brakes snatch, one patch of the tyre can wear faster than the rest, so check the whole tyre for smooth bits and get your brakes fixed.
A tyre can sometimes blow off the rim because the tube was trapped under the edge of the tyre. I’ve had one new tyre explode because one of its wire beads broke. The bike shop replaced tyre and tube, that time.
Things which don’t help, much
‘Anti puncture tape’ which you fit between the tyre tread and the inner tube helps with some brands of tyre. After about a year, though, the tough tape can chafe its own holes in the tube. ‘Kevlar belted’ tyres have the tape included in the tyre. They cost about twice as much as a basic tyre, and help a bit. I don’t believe in flint catchers, loops of wire which are fixed just over the tyre to scrape off any object starting to impale it.
Foam-filled tyres (‘Greentyres’ is or was one brand) don’t get punctures. They do give a very harsh ride, though, are harder work to pedal than pneumatic tyres, and don’t last as long as you’d expect. If you can’t pump up or inspect your tyres, or if a puncture would be a real disaster, they are worth considering.
Puncture sealant, goo you squirt into the tyre, or already in the tube, is not very effective.