Airing up tires on road bike?



DancenMacabre

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Jul 17, 2009
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I know this is a pretty silly, um maybe dumb, question.

When I use a big floor pump to fill the tyres on my bicycle, it sounds like they are sometimes loosing air. When I pump, the gauge number goes up but then it starts dropping until you pump again.

What is the trick to this so you can air up tires without losing air after the last pump and before you remove the line?
 
DancenMacabre said:
I know this is a pretty silly, um maybe dumb, question.

When I use a big floor pump to fill the tyres on my bicycle, it sounds like they are sometimes loosing air. When I pump, the gauge number goes up but then it starts dropping until you pump again.

What is the trick to this so you can air up tires without losing air after the last pump and before you remove the line?

No trick. The air you hear escaping is air that escapes from your pump hose (most likely at the seal between the pump head and your valve stem), not from your tire. The tire valve will close as soon as the pressure starts dropping, so you should not really lose a significant amount of air/pressure in the tire itself.

That said, if you have air escaping in the way you describe, you might want to look into replacing the seal in your pump head.
 
Dietmar said:
No trick. The air you hear escaping is air that escapes from your pump hose (most likely at the seal between the pump head and your valve stem), not from your tire. The tire valve will close as soon as the pressure starts dropping, so you should not really lose a significant amount of air/pressure in the tire itself.

That said, if you have air escaping in the way you describe, you might want to look into replacing the seal in your pump head.

To add a bit to that, I have seen folks push the pump head too far down on a presta valve stem which will hold the valve open, which can cause some funny things to happen.

Like Dietmar said, if you are getting a good seal the valve in the tire stem will open when the air pressure from the pump exceeds the air pressure already in the tire.

Then as you you pull up on the pump handle the air pressure in the tire will cause the valve in the stem to close with little pressure loss.
 
Think I got what you all explained. The seal is prolly why I hear the air escaping.

I will experiment and see if this gets better.

That was helpful guys, thanks.
 

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