Ride UK Tech Columns

#63 Punctures

(This article first appeared in Ride UK issue No. 63 and is reproduced here by kind permission of Ride UK.)

I guess we have all envied after skateboarders once or twice. Usually when your back wheel has just had a little brush with coping and is making that awful hissing noise. Just then the idea of rolling round on a plank with solid wheels that NEVER go pop is pretty attractive.

A couple of years ago I went through a real nightmare with punctures. It seemed that I only had to touch the coping to get a pinch puncture. In one day I added 7 patches to my back wheel. To add insult to injury each time I wanted to remove the tyre it was this awful wrestling match that drove me insane. All this trouble drove me to do some serious thinking about punctures, why was I suddenly getting so many more than usual? And more importantly what could I do to stop them?

The following is my hard won wisdom on the matter. You may think you know how to mend a puncture or get a tyre off, but read it anyway, I bet you will learn something.

Well I am not going to hold back on you, here is the single most significant thing I learnt. Most punctures are, at least in part, due to the rim! That’s right don’t blame your tyre for being a tight fit on the rim when it seems impossible to remove, blame the rim. When you get mysterious punctures in the middle of the night, and come down to find you have a flat you didn’t have the night before, take a long hard look at your rim. Does it have a smug smirk on its face? Does it have a sharp little hole hidden at the edge of the weld? Are the spoke holes bristling with sharp edges? Most likely yes.
Most people run a rubber rim strip or a few layers of electrical tape to cover the spoke holes but these are of limited use. They often move or just plain let the sharp edge poke through. Much much much better is a couple of layers of Duck Tape (Gaffer tape, duct tape, whatever you want to call it, the important part is that it is fibre reinforced and tough). If you split an ordinary roll down the middle you get a strip just the right width to cover the whole inner face of the rim. Just 2 layers should be plenty to let you sleep at night without fear.

There is a definite technique to getting tyres off. If you know it, then you can get most tyres off most rims, without tyre levers and the risk they add of extra punctures.
The key is to understand what you are aiming to do. And the aim is very very simple. All you want to do is get as much slack as possible into the tyre and to get all that slack over to the same side of the wheel.
The tyre bead is reinforced with steel wires that run all the way around the tyre so there is no way you can "stretch" this over the edge. The rim is a substantial aluminium extrusion so there is no way you can compress this to let the tyre off.
What you CAN do is push the bead into the centre of the rim where there is a little dip. At this point the rim has a smaller diameter so at the other side of the wheel we can pull the tyre out over the edge. We also have to contend with the fact that the rubber tyre is very grippy, so while we might have a fair bit of slack in the bead we cant easily get it all over to one place.
If you follow this system you should have a much easier time:-
1. Deflate the tyre COMPLETELY.
2. Pull the bead away from the rim as much as you can next to the valve.
3. Keep pulling the bead outwards and at the same time reach across the wheel to the opposite side. At the other side push the bead into the very very centre of the rim where the deepest point in the channel is. Push the bead down into the bottom of the dip and try to feed the slack round to the valve where you are still pulling outwards.
4. Keep doing this to feed all the slack round to the valve.
5. Eventually you should have enough slack at this point to easily pop the bead over the edge.

Because the dip in the middle is essential to creating this slack some rims work much better from this point of view. Deep Ukais and Alex Supra Es are the hardest to get tyres off and Sun Big Cities are the easiest.

Having got the tyre off we just need to patch it and bung it back in right? And we all know how to mend a puncture don’t we? Well most of us do but I still see an alarming number of people who simply will not let the glue dry before slapping the patch on. SO if you are one of those people, let the glue dry before you add put the patch on! And remember it should be a thin film of glue not a girt puddle of the stuff!

So as a side effect of my puncture epidemic I developed into the worlds fastest puncture-mending machine. You might think this made me very happy, but surprisingly I was still pretty pissed off. I didn’t want these punctures, I wanted to ride.

Nearly all the punctures were pinch punctures, a neat little snake bite caused by the tyre bottoming out to the rim, so I started thinking long and hard about this.
What was going on? There was no hole in the tyre, no evidence of the rim cutting through, so what made the hole? After a lot of thought I decided it was more like a split. After all the holes were always thin slits anywhere from 2 or 3 millimetres to 2 or 3 centimetres long. And often I was getting punctures even though I would swear I didn’t hit the coping that hard. Fair enough I had hung up but I was sure I hadn't hung up so hard as to hit the rim, and there was no corresponding dint in the rim sidewall.
After a bit of thought I decided that the problem was stretch. As the tyre deformed the tyre was deforming into a weird shape. On the inside of the curve the inner tube would have to stretch around the tyre and maybe it was this that was causing the puncture? As the tyre kinked inwards the tube had to follow the curve, and because it would stick so much to the inside of the tyre all the stretch would occur in a very small localised area.
My solution therefore was to "unstick" the tube from the tyre. If the tube could be allowed to slide over the inside of the tyre easily, then the strain would be spread over a lot more inner tube and it might not puncture!

Having worked this out I decided that chalk was the solution. Puncture kits always contained a small block of chalk to rub on the patch to stop it sticking to the inside of the tyre and I reckoned it was worth a go. So I bought myself a huge block of climber's chalk and broke a little corner off. Next time I got a puncture I crumbled it all around the inside of the tyre and rubbed it in with my fingers. And it worked! Overnight I went from a dozen punctures a week to just a couple. A huge improvement. But I still felt it was too many. I no longer got punctures for the slightest brush with the coping but it still seemed I was getting more than my fair share.

In an attempt to further reduce the puncture problems I started putting higher and higher pressures in my tyres. We all know that tyre pressure is crucial. Run too little and every ride is a succession of thuds as the rim bottoms out and punctures become a certainty. Most of us hover around the 90psi mark as a balance between this and bone shaking vibration. Flatlanders and vert riders who live in beautifully smooth worlds run well into the hundreds.
I worked my way up until I was regularly running 140psi (in a tyre rated at 65). Suffice to say my bike was FAST. Unfortunately it was also as rigid as George W Bush's cock at the thought of going to war. Also I wasn’t getting any fewer punctures, and to make matters worse no patch would stay on at that kind of pressure so it was a new tube every time.

It was time for a change in tack. Trials motorbike riders have always run real low pressures for grip, yet don’t seem to get that many punctures. The difference is that they run really really wide rims. So I tried that. I dumped my knackered Alex rims and laced up a pair of Hula Hoops. Overnight I stopped getting punctures. I ran those rims for about four months and only got one or two punctures. Clearly width was the key. So for my next set of rims I got the widest I could find, Sun Big Cities were the widest and I just don’t get punctures anymore.

Yesterday I did a good old fashioned blunt on street. My tyres were way down around 70 or 80 psi and I could feel a sickening thud as the sharp angle iron edge banged into the rim. I waited nervously but… No puncture.

Wide rim + chalk in tyre + Duck tape rim strip = happiness.

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