Mountain bike punctures - valve being torn off.

What pressures are you running? Are the tyres kevlar or wire bead? Do the valves have lock rings to keep them in place? Have you checked the valve hole in the rim for sharp bits?

I run tubeless which gets around such problems although it's a pain in the ass to set up initially and is more picky on what tyres it'll work with. Good for not getting punctures though!

J

I think the problem is probably the low pressure - a good chunk of the friction between rim and tyre is provided by the pressure on the inner of the tyre by the tube. You can try running a few psi higher, or alternatively you can put a few layers of insulation tape (or even better rubber self-amalgam tape) over the spoke tape, i.e. between spoke ends and inner tube; the increased radius and rubber surface discourage the tube from moving.

You can get also get rim tape - double sided tape to go between the wheel rims and the tyre bead, or an extreme solution which I once tried with no success is to cut the tube and shorten it slightly by inserting one cut end inside the other. IIRC, the chap who suggested this reckoned that about 10-15mm overlap was about what you want.

FWIW nomenclature - rim tape is what you're calling spoke tape, and best for all uses I've met is Velox cloth tape. But I've no experience with running at very low pressure.

May be worth asking on rec.bicycles.tech or uk.rec.cycling, since they're pertinent newsgroups. The former certainly has recent discussions of precisely this question. If you can't take the off-topic clutter, just watch the single thread with the question in. Or the Singletrackworld forum?

I thought I'd posted this to URC. My brain obviously wasn't firing on all cylinders this morning. I was wondering what Albert was doing there TBH :D.

Heh :-) I did wonder a bit, since I've seen you on there.

I agree, normally low pressure, and the tube sticking to the tyre and rotating with tyre, because it doesn't have the pressure to hold it all in place.

Try some talk inside the tyre too, before putting it back in.

"Nice tube, please don't puncture again..."?

Have you tried it? Don't knock it. It works ;)

Can't you get rim clamps / security bolts like they use on dirt motorbikes? (a quick google says not) A second (and 3rd if using 2 for balance) hole is put in the rim, a plate sits inside the rim that is bolted though hole to clamp bead to rim.

How long have people been using push bikes to compete on dirt? These have been around in motorbike world for like forever - certainly pre WWII. Standard fitment on world's first "Superbike".

2 and 3 for wm1 2 and 3 rims Still available today for modern dirt bikes. Tyre Rim Clamps/Security Bolts Rubber and steel construction in 1.60,

2.15 & 2.50 sizes £6.95 I don't think any are small enough. Maybe you can make a pair, weld a bolt to a shaped plate with a bit of old inner tube superglued to it.

They do make tyre and tube changing bit more of an arse but don't stop ISDT riders changing inner tube in 2 min flat.

Or drag racers method, a few self tappers though side of rim into bead. They don't need air, just CF the tyre to shape.

The first mountain bike guys started with converted Schwinn cruisers way back when the current indie look was called hippy.

But cyclocross guys have been doing it since the war with dropped handlebars.

Remember, on a pedal cycle in competition, everything you add must have a bloody good reason for being there, because you have to push it yourself, unlike an offroad motorcycle. Even more so in the past when a lot of it would have been made of steel instead of modern aerospace type materials.

If your tyre slips on the rim and rips the valve out it's the end of your race, YOU LOSE. I'd say that an excellent reason.

It's not that massive of a problem. I suspect racers either use superglue or higher pressures - the reason I'm running such low pressures that I'm using high volume tyres on a rigid bike, purely because that way it rides how I want it to - the big soft tyres take a bit of the edge off, but you're still thrown around enough for you to remember that you're riding a bike and not sat in a car (unlike some full suspension bikes I've ridden).

Various reasons they're not used:

Racers don't use tubes. Tubeless is lighter and more resilient to things like pinch flats.

As Doki said, racers would run their tyres harder. Power is limited, so sapping it with squishy tyres isn't good if you want speed.

Good XC racers won't be braking massively either - they'll be carrying their speed through things.