what's it for?

[fossyant]

The Presta valve is held shut by air pressure..... rotating forces will not be enough to open this...come on........

TBH..I'd rather use Presta on 100 psi tyres than schrader....full stop.

Any sudden deflation will be a valve failure..... the lock nut just keeps stuff nice and tight.....

 

[Sittingduck]

I broke the valves on both my first 2 presta tubes during fitting. Both went flat... suggest replacement asap. They're only about 3 or 4 quid a tube so why risk it?

 

[Gerry Attrick]

The Presta valve is held shut by air pressure..... rotating forces will increase this force... i.e. the valve will be forced outwarde - i.e. shut.....

TBH..I'd rather use Presta on 100 psi tyres than schrader....full stop.

Any sudden deflation will be a valve failure..... the lock nut just keeps stuff nice and tight.....

Not wanting to make a huge issue of this Fossy, but I have to say your physics appear a little faulty.

 

[buggi]

okay, i'm putting an end to this debate now. Gerry is right coz i just found this on another forum

"I done exactly the same on the London to Brighton, and my mate recently done the same at Afan - both occasions required a quick change, so in went new tubes. Pumping up tyres hurridly using a mini-pump, which obviously means you are moving the actual valve around alot and the brass centre piece bends or breaks.

Both occasions the tubes went down within minutes of setting off. "

That settles it, off to change my tube. Damn i was sooo comfy on my settee. thanks Gerry

 

[fossyant]

Dodgy pumping up of tyres folks...... there is a lot of pressure in 100 psi, jim will be about to explain the bike will need to do about mach 1...

No dodgy physics...dodgy pumping technique and knackered valves....replace..... I was debating the centrifugal forces........

Change the tube, as I said in my OP.....

 

[Crackle]

I gotta say my view is pretty simple.

If it didn't have it it wouldn't need it, it does so it do.

Anyway how did you break it? I think you need to replace saviour with brain.

 

[Mr Pig]

Why can't they just make a high-pressure version of the Schrader valve and be done with it? let's face it, Presta valves are crap in every other respect.

 

[Gerry Attrick]

Why can't they just make a high-pressure version of the Schrader valve and be done with it? let's face it, Presta valves are crap in every other respect.

I think the problem is that Schrader valves are relatively "fat" and the hole required in a narrow racing rim would cause too much weakness.

 

[fossyant]

I think the problem is that Schrader valves are relatively "fat" and the hole required in a narrow racing rim would cause too much weakness.

Exactly....


The 'lock nut thingy' stops you blowing the valve into the tube when inflating the tyre......

Presta is simple, but you'll see most MTB tubes are moving that way now ?

One Fossy advice here.....

Always buy a good tube..... (e.g. Vittoria Ultralight / Conti Race) are my fave's - I am a Vittoria die hard though for the tubes (not tyres -Mitch for me)........

Cheap tubes lead to problems....... I've been using Vittoria tubes on my road bikes for too many years and have never had a 'problem' valve.........

 

[Mr Pig]

Schrader valves are fat and in a racing rim would cause too much weakness.

Naa, I think roadies are just too stuck up to use any part also found on a car! ;0)

 

[meenaghman]

>>
One Fossy advice here.....

Always buy a good tube..... (e.g. Vittoria Ultralight / Conti Race) are my fave's - I am a Vittoria die hard though for the tubes (not tyres -Mitch for me)........

Cheap tubes lead to problems....... I've been using Vittoria tubes on my road bikes for too many years and have never had a 'problem' valve.........
<<<

Well I'll add my two pennys worth here.. I find tyres and also inner tubes made to slightly different sets of measurements.. so Vittoria, Michelin, Continental and Schwalbe seem to be harder (vittoria) or easier to fit (Schwalbe) on rims. I believe the inner tubes are made to similar measurements.. thus in theory running a vittoria tube in a Schwalbe tyre requires one to inflate to far higher pressure than running it in a Vittoria tyre to get the same level of hardness.. I normally inflate to 100-110 PSI and recently put some Contis on my rims with vittoria tubes and found that they required an extra 10 psi to make them that bit harder... otherwise I felt they weren't hard enough. I reckon this was the reason for a spate of blow outs I had. Switched to conti tubes with the conti tyres and things have been fine.. and they seem to be my level of hardness @ 100-110 PSI. I was using Vittoria tubes with Michelin pro 3 and found them fine but the GP4000s conti tyres seem to be a bit fatter than the Michelins,(both 23 tyres) take more air to fill, and as a result the inner tube needed to be inflated more and thus a higher pressure to fill the tyre properly.. well thats my theory on it.. or maybe I just had a bad batch of tubes.

 

[dellzeqq]

talcum powder! Insist on it!