On Thu, 05 May 2005 17:39:02 +0100, BigBen
<
[email protected]> wrote:
>On Thu, 05 May 2005 08:45:21 -0400, dvt <[email protected]> wrote:
>>I've used these for years with no problem whatsoever:
>>
>>http://tinyurl.com/ddo8m ...or...
>
>I some just like that, but without any rubber o-ring. Could that make
>a significant diference?.
>
>Also, what's the point of the metal cap on the Presta valves, which
>have to unscrew to inflate the tube, and then screw back?
>
>Regards,
>BigBen.
Dear Ben,
That's a lock-nut that makes sure that the wedge-shaped
Presta valve is pulled up tight and stays that way. Unlike a
Schrader valve, there's no internal spring to keep it in
place. (The Presta can get wedged into place, so to top up a
low bicycle tire you often have to over-pump before the air
pressure blows the valve open. Doing this on a floor pump
with an air gauge affords idle amusement.)
You have to have an O-ring seal that tightens around the
valve to pump up a Presta valve. Most pumps have a thumb
lever to tighten things, but air-hose Presta chucks often
just push on and off, relying on instant pressure to seal
the O-ring.
Places like
www.performancebike.com and
www.nashbar.com will
sell you sub-$25 frame, mini, and even floor pumps with
heads that handle both Schrader and Presta valves, either
with two holes or else quick-remove-and-reverse designs.
They work fine.
http://www.performancebike.com/shop/category_tools.cfm
http://www.nashbar.com/subcategories.cfm?category=106
They often have sales and coupon codes:
http://www.edealinfo.com/Coupons/performancebike.shtml
http://www.edealinfo.com/Coupons/nashbar.shtml
I finally broke down and bought a handsome yellow floor pump
on sale with a nice pressure gauge and dual chuck and have
to admit that I use it at least as often as my air
compressor. This may be it:
http://www.performancebike.com/shop/profile.cfm?SKU=16031&subcategory_ID=4360#
Among other reasons, the Presta valve is used on bicycles
because it's so thin and a tiny bit lighter.
The thinness means that the hole in a narrow racing rim is
smaller, so the wheel is a bit stronger. The bicycle tube
volume is so small compared to a tractor tire that the
slower inflation rate doesn't matter.
The lightness is psychologically important.
Carl Fogel