james_giant wrote:and Dougal, whats the lateral force on a tyre? by lateral I mean sideways when you are hard out cornering.

That's a hard one to quantify on a bike, because you lean into the corners you're effectively putting all of your weight on the same line as you would when you're upright.

In that case on a hard surface, the lateral force is your weight times the sine of the angle you're leaning at (zero degrees being vertical). 30 degrees lean makes for the lateral force of half your weight.

If you lean more or less than the bike or ride on soft ground, it gets much more complicated. Let alone the proportion of weight on the front/back through a corner.

Well, if ghetto tubeless tyres can 'burp' air out, I would have thought that with a tube the surface on the tyre can move on the rim as well...

Ive never have burpage on my ghetto tubless,and I run em soft and ride em hard*.

Possibly cos the rimstrip is actually glued to the bead of the tyre by the latex now.

Which may make tyre removal "interesting".



*Make of this what you will.

Dougal wrote:

james_giant wrote:and Dougal, whats the lateral force on a tyre? by lateral I mean sideways when you are hard out cornering.

That's a hard one to quantify on a bike, because you lean into the corners you're effectively putting all of your weight on the same line as you would when you're upright.

In that case on a hard surface, the lateral force is your weight times the sine of the angle you're leaning at (zero degrees being vertical). 30 degrees lean makes for the lateral force of half your weight.

If you lean more or less than the bike or ride on soft ground, it gets much more complicated. Let alone the proportion of weight on the front/back through a corner.

so 280+ lbs? me being 200.

I was thinking that this force would have been more than the tube vs tyre pressure or at least enough to cause movement betwen the two. Granted I havn't done physics since 3nd yr uni may many moons ago.

Also wouldn't the motion of a tyre rolling over a root or rock cause movement between the two surfaces? I mean normally both are working around a very large axis 26" and are then forced to move around a axis as small as two inches.

james_giant wrote:Also wouldn't the motion of a tyre rolling over a root or rock cause movement between the two surfaces? I mean normally both are working around a very large axis 26" and are then forced to move around a axis as small as two inches.

I don't believe they move in normal use, I think the flexible tube simply moves with the tyre. If there was a degree of rubbing movement, you'd notice wear over time on the inside of the tyre and the outside of the tube.
If the pressures get low enough (like flat) you do get movement which can be seen by folds wearing in the tubes. At this point though the tyres aren't resembling round any more.

I've had many stick themselves together pretty well, they definitely weren't moving.

Are you pumping up your tires reguarly? I had a similar problem with one of my tubes and I was alwas pumping up and letting down the tire for up and downhills. I'm a bit of a Timmy when it comes to pumping up the tire with my hand pump and as I was jiggling it when I pumped it up it was slicing around the valve.

Mals wrote:Are you pumping up your tires reguarly? I had a similar problem with one of my tubes and I was alwas pumping up and letting down the tire for up and downhills. I'm a bit of a Timmy when it comes to pumping up the tire with my hand pump and as I was jiggling it when I pumped it up it was slicing around the valve.

I think Mals has tumbled (well Timmy'd) upon the problem.
I wonder if you used a track pump... all your problems would disappear?

Incidently, I use DH tubes + Michelin tyres - so I guess punctures are never really gonna be a problem

Stun wrote:I think Mals has tumbled (well Timmy'd) upon the problem.
I wonder if you used a track pump... all your problems would disappear?

Incidently, I use DH tubes + Michelin tyres - so I guess punctures are never really gonna be a problem

My riding is at a very unsophisticated level right now (I hope that will change by next summer) so no dicking around with the pressure. My tyres are old smokes and the tubes are whatever is in stock. I don't get regular punctures, just valve probs. Infact, I've done two touring trips and I think on both I only got one puncture. My girlfriend, on the first trip, had huge problems with spokes - long live stainless steel, regular sized wheels and bike stores that don't mind crazy kiwi girls taking over.

I only ever use a track pump. I keep meaning to get a proper pump to carry on the bike when riding since the last one died, umm years ago.

Hmmmmm... so it's not the pump.
Back to the drawing board me thinks...

Just found this thread (and forum!) through Google as I've got a similar problem at the moment. I've got (presta) valves pulling out of the tube at their base. It only started recently on a set up that's been bombproof for months (Diesel 2.5s on mavic d321). (3 different brands of tube so far - so that's not the problem)

I'm pretty sure that it's the tyre slipping on the rim causing pull on the vavle - it's on a singlespeed and there's quite a bit of torque going through the back tyre on steep climbs, especially now it's drying out here (UK) and grip is improving.

My first guess is that the rim tyre contact is just too dirty to grip well enough - so I'll be just cleaning everything up, maybe wipe down the bead with some meths or something.

On the talc or not thing - I don't reckon that talc will provide enough lube to stop the tube moving with the tyre in a one-off slip - but it probably does provide enough movement between tube and tyre to stop the tube moving with the tyre as it creeps around the rim (which it will do at low pressures as the tyre deforms at the point of contact).. just an idea

yo sweet you have diesel MTB tyres? *goes to google*

wicked 2.5's

Yup - very pleased with them. About 10 months on them so far and they're good in most conditions (heavy mud being the exception) and they're wearing very well too

Oh - and they look the bollocks ;-)

You could try 4 little dots of super glue in the 12, 3, 6 and 9 o'clock positions between the bead and rim on one side only of the tire....

I would mark the tire and rim in one spot and watch it to see if, when, how far and how often the tire does rotate about the rim.

No point in gluing your tire to the rim if the tire is not actually moving.

We used to do this when I was road racing motor cycles so we could eliminate causes of chater.