10 March 2014

On Punctures

Todays post is a rambling one about the one thing all cyclists hate - punctures! I had remarked earlier that I seemed to be lucky to have fewer than average flats on my rides, only to find that my rear tube had developed a slow leak (after the Devarayandurga ride) and was flat in a couple of hours after I got home. It must have happened in or very close to campus, because I'm sure the tire was fine until then. Finding this puncture was tedious - it was imperceptible to the ear or lips, and was found only after I submerged the tube in a bucket. As expected it was a tiny hole.

Glass Marking Pencil
To mark the spot I use a glass marking pencil which sits neatly in my kit along with a small sharpener. (I don't use chalk - it just makes a ghastly mess.) It is essential to mark the spot accurately so the patch ends up centered on the puncture. Patience is the key. So is practice. This applies especially to randonneurs and bicycle tourers. You can (should) "simulate" on road repair by using exactly the same tools you carry, but in the comfort of your home or locality. You might even want to try doing this in the dark.

Next, make sure you locate the source of the trouble. If you patch the tube and leave the thorn in the tire its going to be a lot of wasted effort. Simply replacing the tube will only give you additional punctured tubes. A common tip is to align the name/brand mark of the tire with the valve on the tire so its easy to locate what caused the flat - visually first, fingers next. Be very careful, though - a shard of glass in the tire might cut you very badly.

Some riders patch the  tube, but put in a fresh tube - it saves some time, and is insurance against a failed patching. Make sure you are familiar with your pump, too. Try to inflate your tires and home and see whether your pump can actually reach the required pressure. This will also help you arrive at a comfortable position/posture for using the pump. Pumping can be hard work, especially high pressures or volumes, and in general, bigger the barrel of your pump, easier it gets.

Don't forget sandpaper in your kit. It is needed to remove the "surface" of the tube, as Jobst Brandt describes here. Some people carry sadpaper stuck to an icecream stick, but I find its easier to wrap the sandpaper on the back of my pencil and rub the tube with it.

One last point on equipment. I used to have steel tire levers (not great quality - they had some burrs on the edges). On one long bumpy ride to Anchetty the tire levers punctured the tube of rubber cement, making a red gooey mess in the rack bag, ripped a hole in the bag and nearly fell out and off the rear rack. Luckily the spare tube was spared (no pun intended!). Immediately thereafter I got a pair of plastic tire levers, and now I wrap all the tools in a rag in my kit pouch, held by a rubber band so things don't rattle around.
One last photo before I close - the day after Devarayanadurga I got my first snakebite flat (a.k.a pinch flat), so here's a photo. Enjoy!

Snakebite flat on a commuter bike tube showing the distinct two punctures symmetric about the tube axis
Snakebite puncture

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