Pressure question on road tyres

[Cyclist33]

Hi

Does anyone know roughly what %age of pressure is lost when you release the pump from a valve on a clincher-style road tube/tyre?

So if I put in, say, 100psi, what will it actually come out as?

Thanks

Stu

 

[Angelfishsolo]

Hi

Does anyone know roughly what %age of pressure is lost when you release the pump from a valve on a clincher-style road tube/tyre?

So if I put in, say, 100psi, what will it actually come out as?

Thanks

Stu

I don't think that is easily answerable. I am guessing it would depend on the value, the speed at which the pump comes off the width of the tyres and many more things I can't think of.

That said usually one push of a track pump more than required is adequate.

 

[Cyclist33]

Thanks for that honest if unfulfilling answer

I figured it would involve too many variables to be able to just say "10%" or whatever. I will just whack 105 in tonight and see how it goes tomorrow.

Cheers

Stu

 

[John the Monkey]

Presta?

Should just be the pressure in the hose of the pump, unless you knock the valve nut taking the pump head off.

 

[Angelfishsolo]

Thanks for that honest if unfulfilling answer

I figured it would involve too many variables to be able to just say "10%" or whatever. I will just whack 105 in tonight and see how it goes tomorrow.

Cheers

Stu

I would say that if you can take the pump head of quickly and in one smooth motion then the pressure will be fine.

 

[benb]

Seeing as it doesn't really matter if you're a few psi over or under, I wouldn't let it worry you unduly.
Just stick an extra stroke or two on the pump once you get to the required pressure if you must.

Sometimes I have to give the pump head a good wiggle to get it off, and what sounds like a lot of air hisses out. Tyres still feel nice and solid afterwards though, so not that bothered.