Bicycle Mechanics - Need advice on tire inflation technique

Hi all, I am a newbie and am having some problems keeping my tires properly inflated. I have presta valves and a new Joe Blow Pro Topeak floor pump. My recommended tire pressure is 120lbs.

After I inflate the tire to 120 and then attempt to remove the nozzle from the valve there seems to be an unavoidable gush of air upon removal that I think may drop my pressure significantly. Is there a way to avoid this? Must you over fill your tire by some 10 lbs or so to compensate for this leakage upon removal of the nozzle? The pump seems to be very good and even has a bleeder valve to zero in the pressure but it seems to be for naught if so much is lost upon removal of the nozzle.

Any help or advice would be greatly appreciated as I am participating in my first 50 mile ride tomorrow and want my tires to be properly inflated.

Thanks, Dr. Mike

Don't sweat it, doc. That's just the pressurized air left in the hose escaping.You are not losing air from your tires.

...there seems to be an unavoidable gush of air upon removal that I think may drop my pressure significantly. Is there a way to avoid this? Thanks, Dr. Mike


The air being released is the air contained in the pump and its hose. It's not air escaping from the tire.


That is the beauty of the presta valve design. The presta valve seals due to the differerntial pressure inside and outside the tube. When you are pumping the tire, the relatively high pressure in the pump opens the valve and allows air to enter the tube. When you release the locking lever on the pump head, there is a huge pressure differential across the valve (inside tube = 120 psi, outside tube = 14.7 psi) and the valve shuts. However there is still air in the pump (at 120 psi) that needs to escape somewhere and it exits the pump through the hose.

The Schrader valve operates on a spring loaded valve. When the pump head is inserted into the valve, the valve's spring loaded piston is depressed, which opens the valve - air can go in or out without discrimination. When you unlock the pump head and with the pump head still on the valve, you can get an escape of air from the tube. Hence, for a Schrader valve, it is essential to remove the pump head as quick as possible so the spring loaded valve can close.

thanks guys, the info. is greatly appreciated !


Dr. Mike

And if the spring loaded valve us broken just as you insert the pump.

Then GG.

(True story, happened to me, pure gay I tell you)