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> Tubeless with presta
bobosola
post Oct 1 2009, 07:06 AM
Post #21


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Joined: 22-June 06
From: Locks Heath, Hampshire



QUOTE(Chris M @ Oct 1 2009, 06:44 AM) *
I suppose there's the issue of the initial seating of the tyre, i.e being able to use a garage airline, but wouldn't a Presta-Schrader adapter get over that one?

I ghettoed with Presta originally. The smaller holes do make the initial seating harder with a track pump as it's hard to get the air in quick enough. It can be done though - it's just that Schrader is easier for hand pumping. A compressor will certainly get over the problem, as you say. However, you may find on close inspection that your rim holes are in fact already drilled for Schrader but are sized to Presta by a reducing collar - my Mavics were like that. I thought initially it was a drilled reinforcement lug around the hole area but it was in fact just a press-in plastic collar. All you need do then is pop out the collar and buy Schrader 20 inch tubes instead.


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Mad Pierre
post Oct 1 2009, 07:35 AM
Post #22


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Joined: 2-November 05
From: Melton Mowbray



There's nowt wrong with Presta unless you're a fat handed twit!

Proper UST uses presta valves. You can buy the valves from Just Riding Along with removable cores but removing the cores is not the easiest way to put sealant in. Just leave a small amount of bead off when fitting the trre and pour it in before finishing fitting the tyre. Dead easy!


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Chris M
post Oct 1 2009, 07:42 AM
Post #23


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Joined: 18-March 07
From: Kent



Thank you biggrin.gif

Bobsola, I'll certainly investigate the rims, that would make life a whole lot easier cool.gif if not though, I shall get the removeable core Presta's.

Mad pierre, I am a fat handed twit but still manage ok with Presta tongue.gif biggrin.gif

I appreciate what you're saying about adding the sealant, my trouble is that being a bit cack handed, I can see myself confidently sloshing away only to find that I've filled up my shoes with the stuff laugh.gif
A removeable core would just make life that little bit easier. I don't mind a bit more struggle to initially set the system up because, from what I've read, once it's done I hopefully won't have to worry again untill the tyres need replacing, which sounds good to me biggrin.gif

Cheers

Chris smile.gif


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Jarl
post Oct 1 2009, 09:48 AM
Post #24


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Joined: 12-November 06
From: Bath/Hampshire (uni/home)



QUOTE(Rod @ Oct 1 2009, 12:29 AM) *
I've heard it said / read that the pin on the presta gets physically pushed in by the pump adaptor. This way you don't have to overcome the air pressure against it before air goes in. However, air pressure being air pressure and all values being equal for a given for a cross-sectional surface area... I personally don't know about this theory. I suggest it is down to the sectional area of the aperture? I've not done the calculations but I guess the sectional cross section is about twice that of the presta in the Schrader? This in turn means there is less psi presenting to the inlet making it easier for a given pump to excert enough pressure to blow past the schrader valve or go down the throat of the presta.

BUT I guess you are going to tell us all anyway? biggrin.gif

Rod


Well, I can see where you're coming from now but it's not the case; if anything, it's the opposite. The schraeder valve gets depressed when you put the pump on (hence the hiss) and the presta tip is free floating, so will come back up and seal when you're not pumping. Also, schraeder has a larger cross sectional area and IME passes air better- prestas tend to heat up quiet markedly with vigorous pumping, whereas a schraeder will only get warm after a session of trying to get a tyre to seat.

Going into the physics a bit more, the smaller section of the presta means that a smaller force (as you stated in your post) is needed to overcome the pressure keeping the presta valve closed, whereas it depends on the pump as to how much force is needed to overcome the pressure at the anti-blow-back valve of the pump, but it's near certainly more. This could well be why presta has a reputation of "high pressure", but given it's tendency to overheat, I wouldn't want to be pumping a high volume tyre to high pressure through one sneaky.gif


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Gareth
post Oct 1 2009, 03:36 PM
Post #25


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Joined: 28-July 04



Proper UST has a superior fit to the rim well prior to inflation so needs less air pressure to get the tyre to pop up on to the rim. Ghetto conversions can be adjusted to fit with the addition of a layer or more of foam tape e.g. from Maplin.

If you're going Ghetto it is an advantage to use a Schraeder valve with the core removed for the initial 'airing up' as you get a better air flow (even with a compressor - more air always makes things easier).

The main advantage of Presta is that you can have a smaller hole in your rim because a big hole in a narrow rim can be a bad thing strength wise. It also has an integral 'cap' as the lock nut covers the inlet.

Schraeder needs a bigger hole (at least 8mm) so is not as well suited to very narrow rims. Dirt in a Schraeder valve can cause slow leaks so it's best to run a valve cap (prferably O ring sealed like the metal ones from justridingalong) at all times. The justridingalong valve caps incorporate a really handy valve core extractor too.

Some Presta valve stems are made from soft cheese and you don't need to be that fat handed a twit to bend them with a clamp on mini-pump. rolleyes.gif I like pumps with a hose connector partly for this reason - they also make pumping easier as you can flail about a bit without pulling on the valve. cool.gif


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Chris M
post Oct 2 2009, 07:40 AM
Post #26


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Joined: 18-March 07
From: Kent



Thanks Gareth,

I'm hopefully going to tackle this at the weekend, one way or the other. I must admit I'm tempted to drill the rim if required, I'll have a good look and make a decision which route to take.

I was, quite literally, a few yards into a night ride last night when a talon-like thorn flattened the front tyre.

Even without all the other benefits of tubeless, just to avoid hassle like that will make it worthwhile cool.gif


Cheers,

Chris smile.gif


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