Bicycle Mechanics - Total newbie pls help
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03-12-05, 08:38 PM
Hi. I am fully aware this is a completely ridiculous question, but I am totally serious. I am trying to pump my tires for the first time (until a few days ago I was not even aware I had to do this regularly, I thought it was something you did after fixing a flat), but when I remove the pump from the bike (I don't know the technical terms...), when I tighten the screw on the tire to stop the air from coming out, because I am not fast enough, some of the air escapes--therefore, defeating the whole purpose of pumping the tire. I was told to pump it to 100, I tried to be sneaky and pump to like 120, so when some of the air escapes right away, it's still at about 100--but I can bet it's below that. What do I do so the air I just pumped in doesn't go out when I disconnect the pump from the bike? I don't know if this info matters or not, but it's a Presta valve (Specialized Dolce Elite), and the pump is a floor pump (JoeBlow) made by Topeak.
Thanks so much! Sorry for my ignorance. I am a very non-mechanically inclined girl... who is new to biking... I have a ride tomorrow AM with a group and I have to make sure my bike is ready...
Once you remove the pump from the the valve stem, no air should escape from the tube unless you press the end of the valve. Inside the tube, the air pressure forces the valve closed. When you tighten the nut on the stem, try not to press down on it and you should be able to tighten it without air loss.
Don't tighten the nut very hard. Just snug it in place.
03-12-05, 09:03 PM
Thanks. Tried again-same thing-some air comes out, and then it stops. The tires are pumped ok though--I've had it worse... so hopefully I'll be fine tomorrow. I am planning on going to a bike maintenance class on Wed, so hopefully I'll learn this stuff there.
Unless something is wrong, most of the air you hear coming out is coming from the pump itself - releasing pressure.
03-12-05, 09:35 PM
the most common mistake i see people make with presta valves is that when they tighten the little nut, the push down at the same time. So try not to do that, althouhugh it often happens without realizing you have done it until you hear the air
03-13-05, 03:04 AM
when I remove the pump from the bike (I don't know the technical terms...), when I tighten the screw on the tire to stop the air from coming out, because I am not fast enough, some of the air escapes--therefore, defeating the whole purpose of pumping the tire.
Not to worry. The air that you hear escaping is coming from the pump hose. Your inner tube has a poppet valve in it that the air pressure inside of the tube pushes shut as soon as the air pressure on the outside of the valve stem is released. If you squeeze your tire after you are finished, it should feel nice and hard.
I'm new to the presta valve also. I've found that pushing the valve stem sideways also will unseat the valve seat and allow the air to escape. If the air is escaping while you're disconnecting the pump then it's as the others said, it's probably the pressure releasing from the pump and not the tire.
If the air is releasing as you're turning the nut, then either you're pushing the stem inward (or sideways) or the valve is faulty.
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