Why do riders puncture so often?

A rider punctures in a race. They’re forced to stop and to stand by the side of the road, often holding up a wheel in the air with a forlorn look on their face. You’ve probably seen it on TV many times, maybe you’ve experienced it too.

Hopefully the rider will get a spare wheel and return to the action. But precious energy is wasted and when the pace is high the rider can lose time and placings. Look to Sylvain Chavanel in Paris-Roubaix last Sunday. One minute he’s at the front of the race, the next minute he’s out of contention. It happens so many times a year it seems normal. But is it? Would you work with a tool that let you down so often? If a rim or a crank failed this often nobody would use it.

An outsider to the sport would probably be amazed by the number of punctures that happen in a race. The energy wasted, the races lost, these incidents aren’t a mere inconvenience or hassle. Punctures cost results and points. At times even careers and reputations can be ruined. Why?

First let’s look at the basics of the technology. The “tubular” used by most riders in the pro peloton. It is made from cotton fabric that is stitched around a rubber inner tube. This is then given base tape on one side and on the other first a layer of puncture protection is added and on top of this the rubber tread is added. The advertorial here explains it well:



The puncture protection is usually a layer of special material, for example kevlar. Here a tough material is woven very tight. The rubber tread is soft for grip but a small piece of glass or flint can easily pierce and the protective layer is meant to stop sharp objects reaching the inner tube. But too much of this protective belt makes for a heavier ride, the material does not deform like the supple cotton or soft rubber.

How?

Obviously a puncture happens when an object manages to pierce a hole in the inner tube. Sometimes this can happen quickly, you ride over a tack and it goes straight in. Don’t forget the weight of you and your bike is spread over the tiny contact patch of the front and rear tyres, if you go over some glass with a sharp edge then even “bullet proof” kevlar can yield. Often it can happen slowly, a shard of glass little bigger than a sugar crystal can slice into the soft rubber treat and sit there, gripped by the rubber and silently slicing away towards the inner tube during hundreds or thousands of wheel revolutions. As you can imagine it is hard to prevent this.

There’s also another type called the “snake bite” puncture when you hit an object like a kerb or the edge of a pothole hard. The whole tyre compresses and the inner tube is torn against the sidewalls of the rim, creating two parallel holes… as if a snake’s fangs bit the tube.

Why do riders puncture so often in races?

Maybe they don’t. Instead it could just be that we see a handful of riders puncturing yet 95% of the bunch are fine. There are no statistics on this. But there are plenty of stories of riders losing a race thanks to a puncture at the wrong moment.

There are differences for pro races. Riders have their jobs on the line so they’ll think nothing of trying to chancing their $2,000 wheels over a sunken drain-cover and the impact can cause a puncture, either the snake bite variety or by slamming any shard of glass or stone home into the tube. Also in a race every bit of the road is used, including the gutter and other places where debris lies. In training you’d avoid these things. This might help explain the high frequency of punctures.

It needn’t be this way

There are technical solutions. You can put sealant in the tyre. This is liquid that you pour into the inner tube and then inflate. In the event of a puncture it is blown out of the hole but solidifies to block the hole.

It’s been used in the past but only rarely. For example FDJ used sealant with tubeless tyres in the 2009 Paris-Roubaix. But a year later Bikeradar.com did a piece called Liquid insurance – the policy no one’s buying at the Tour de France and the reason why teams didn’t use this technology? Conservatism seems to be one factor. “Weight and [lack of] familiarity” says BMC whilst Saxo’s mechanic said “I don’t know if anyone else does or not but we don’t. We were thinking about it. The tyres are pretty good and we don’t get punctures like years before“.

I don’t see weight as a problem. For sure, if you have a pair of featherweight carbon wheels at 1100 grams a pair then you want to save every gram. But add 250 grams per tub and the wheel + tub weight is 1600 grams. Would a rider notice 30g of sealant in each tub, an additional 3.7% in weight? Perhaps but they’d be like the Princess sleeping on the Pea and besides they’d surely notice ride to the finish whilst others around them punctured.

The big problem with the sealant is that it dries out, leaving residue inside. For the amateur, this means topping up with more liquid every few weeks and adding more weight, effectively ruining the inner tube too, especially if the sealant comes with strong chemicals like ammonia. But pros have an advantage here because they use new tubs all the time, tubs are binned so frequently that injecting sealant isn’t a big deal.

But it turns out some teams are using this. I started a draft of this piece last week and a day later it turned out via Velonews that Sky were to test a sealant during Paris-Roubaix. Presumably NewsCorp didn’t hack the blog. Better still, the team didn’t have a single puncture in the race.

Tubeless future?

Tubeless tyres are rare for now but could take over the market in five years’ time. Like a car tyre they don’t have an inner tube but instead rely on the bead to make an airtight contact with the edge of the rim. Done right and you save the weight of an inner tube and reduce the risk of punctures because the tube won’t burst like a balloon. You can put sealant in and with the right technology the rolling resistance – how fast it rides – can be superior. It’s already widespread in mountain biking.

Summary

Everyone hates a puncture. There’s never a good time. But try to imagine it costing you a big bonus at work or even the chance to etch your name in to the history of the sport? Given punctures are so costly to riders and teams I’m still surprised they happen so often. But the technology is hard to perfect. Just as you wouldn’t want to go running with a bullet-proof vest, rolling on puncture-proof tyres would be equally awkward.

The future could be different for pros and amateurs. Pros can run some sealant and ignore the cost but I doubt ordinary consumers would appreciate this. Longer term tubeless could be the answer, offering low rolling resistance and sealant.