Spring is nearly here in the UK, which means more hours of daylight and (we hope) better weather to get out for some nice bike rides in the countryside. The roads and tracks, however, are still covered in mud, grit, stones, thorns and twigs. So it’s a good time for another look at the cyclist’s old foe the Puncture Fairy, with her bag of magic drawing pins.
Last time I discussed some simple techniques to reduce your chances of a puncture without spending money. This time I’ll consider ways of toughening up your tyres.
1. Puncture-proof tyres
Most bikes today have ‘clincher’ tyres. A clincher tyre has two parts: the ‘inner tube’, which holds the air, and the outer tyre, which has a U-shaped cross section and fits over the inner tube, hooking onto the rim of the wheel. The outer tyre is usually made of at least two layers. First there’s the ‘carcass’, which is made from woven nylon or similar fabric, coated thinly with rubber. This makes the shape of the tyre. Then on the outside, where the tyre contacts the road, there will be a thicker rubber strip – the ‘tread’.
Puncture-proof tyres have another layer in between the carcass and the tread – the ‘puncture-proof strip.’ This is normally made from a light but tough inflexible material such as Kevlar (the stuff they make bulletproof vests out of), but it varies widely. In some tyres it’s just a layer of harder rubber. Because the puncture-proof strip is embedded in the tyre, it’s not protecting the outside of the tyre. Thorns and flints can still stick into the rubber tread layer; what the puncture-proof strip does is prevent the thorn from passing all the way through the carcass and into the inner tube. Looking at the picture, you’ll see that the strip doesn’t go all the way round. The sides of the tyre (‘sidewalls’) are relatively thin and unprotected. Some tougher tyres add extra rubber coating on the sidewalls.
Because pointy things can still get embedded in the outer tread, it’s best to check your tyres occasionally for sharp objects sticking into them. An unattended flint can gradually be pressed further and further in as you ride, eventually working its way through the puncture-proof strip and into the tube, causing a delayed-reaction puncture perhaps days after your tyre originally picked up the object.
So, a tyre with a puncture-proof strip will stop your inner tube from puncturing… most of the time. In reality it won’t be proof against everything, so you still need to be prepared for punctures. The tougher the puncture-proof strip is, the more heavy, rigid and uncomfortable the tyre may be to ride – especially if the sidewalls have also been toughened. Keen cyclists talk about the tyre being less ‘supple’. In reality most puncture-proof tyres are a balance between protection and performance.
Are they worth having? Definitely. The undisputed champion of puncture proof tyres is the Schwalbe Marathon Plus. If avoiding punctures is what matters most to you, go for a pair of them. But be warned that they are heavy and inflexible, so may reduce your enjoyment of riding the bike slightly. On the other hand, you might consider that a fair trade-off to avoid being stuck by the roadside as the rain comes on.
2. Solid tyres
Back in the good old days, most bikes had tyres made of solid rubber, or leather, or possibly even wood. Then along came John Boyd Dunlop in 1888 with the idea of an inflatable tyre to alleviate the jarring effects of the road on his young son’s tricycle. The rest is history. But why? When pneumatic tyres are so prone to failure, why do we use them so much? Apart from opening the door to the Puncture Fairy, what did John Dunlop ever do for us cyclists?
Well, there’s the handling. And the rolling resistance – far less on a pneumatic tyre. And of course the comfort. And the weight.
Modern solid tyres are an attempt to find the best of both worlds: a tyre that can’t be popped with a drawing pin, but that still has some of the handling and shock-absorbing capabilities of an inflatable tyre. Every few years some inventor claims to have created a solid tyre that will revolutionise the industry, gets a few mentions in the papers, then disappears from sight (probably into bankruptcy).
Typically a solid tyre will have a solid outer covering over a bubbly, foamy honeycomb centre (mmm… excuse me while I go and have something to eat). The thousands of tiny pockets of air in the honeycomb section are independent of each other, so popping one makes no noticeable difference. The problem is, that foamy layer tends to be too soft or too hard, but never ‘just right’ for cycling on. Air-filled tyres have some fascinating physical properties which I won’t bore you with now (because I don’t understand them all) but it turns out it’s very difficult to emulate them using bubbly synthetic foam. Solid tyres have a reputation for being slow, heavy and poorly-gripping, with a tendency to ‘bottom out’ on corners – i.e. to squash up so much the wheel rim bumps against the road – or worse still, detach from the wheel.
The latest attempt to garner publicity is the Tannus solid tyre. This has a few drawbacks: it’s expensive (£90 a pair) and difficult to fit: one user advised, “Get someone else to fit them. Anyone else, maybe someone you don’t like or just a bike shop that are up for a laugh.” But with a claimed lifespan of up to 9,000 miles and no flats to fix, you don’t have to buy them or fit them very often. While the Tannus sounds better and more secure than many previous solid tyres, the consensus seems to be that it is slower-rolling than a traditional tyre and a little less comfortable. For cycle touring I can bear the slower speed, but I like my comfort.
‘Slime’ is a brand name; other products are also available, as they say, but none of the others has such a good name. It’s a gooey green liquid that you squirt into your bike’s inner tube. If the tube punctures while you’re cycling, some of the slime fills the hole and sets solid, preventing further air loss. With tiny holes you might not even notice the puncture happened. You’ll still want to carry a pump, though, because with larger holes most of the air may escape before the sealant can do its job. And with even larger holes (bigger than 3mm) Slime can’t cope at all, at which point you’re faced with the prospect of repairing an inner-tube and tyre that are covered in green goo.
Slime also has a reputation for blocking up the tube’s valve, making it harder to inflate. Slime adds weight to your inner tube – about 120g (4oz) per tyre. That’s not a lot, but ‘rotating weight’ added to the wheels is more noticeable than dead weight elsewhere on the bicycle.
You can buy inner tubes pre-filled with slime, which is more convenient and less messy than squirting the goo in yourself.
The makers of the original Slime claim that it’s green in more than one sense: it’s non-toxic and water-soluble, which can’t be said for some of its competing products
Once again, it’s a trade-off: for the convenience of avoiding punctures most of the time, you have to work a bit harder when pedalling , and when you get a bigger puncture it’s harder to sort out. It is, however, a cheap and relatively easy way to improve puncture resistance on your bike.
4. Tubeless tyres
Not to be confused with ‘tubular’ tyres, tubeless tyres are a recent innovation. Someone somewhere thought, ‘Hey, what if we just made the wheel rim airtight and the tyre really close-fitting, like a car tyre, then squirted in some of this Slime stuff to seal the rim and the tyre together? Then we could throw away the inner tube and just pump the tyre up.’ The result has become very popular in mountain biking circles, and is beginning to be seen on road-going bikes.
Besides a special tubeless tyre, your wheel rims need to be designed (or converted) for tubeless use. The initial installation can be challenging, but once they’re on they should be trouble-free for a good while.
Aside from puncture-reduction, another advantage of tubeless tyres is that they can safely be run at lower pressures then equivalent-sized conventional tyres, meaning more comfort and better grip when going off-road. (In a conventional tyre, low pressure means more risk of ‘pinch punctures’, where the inner tube gets squashed between tyre and rim. No inner tube, no pinch punctures.)
The drawbacks: Again, if you get a big puncture the slimy sealant won’t cope and you face a major – and messy – repair challenge. Some riders carry a conventional inner tube to put into the tyre at this point; others phone for a lift home. Local bike shops may not have the spares for you, but that will no doubt change in time.
And the answer is…
It’s hard to say. I’m tempted to ‘go tubeless’ on the mountain bike. If the Tannus solid tyres come down in price they’re probably worth considering for a commuter bike that’s used for short journeys. For my other bikes, I’l be sticking with decent puncture-resistant tyres, conventional inner-tubes and (for journeys longer than the trip into town) a spare tube and a puncture repair kit. Sometimes the old ways are the best…
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