Loss of pressure as you disconnect pump...

[WJHall]

Pressure gauge? When I did cycling proficiency about 1962, they just said pump tyres up board hard. So I go about half a bar over to allow for any air that may escape from the tyres due to a fumbled disconnection.

 

[tyred]

The traditional Dunlop/Woods valve doesn't even allow you to check the pressure and people seemed to manage at the time.

 

[Danny]

I agree with Spire - you can definitely get a small rush of air from the valve. But I do think it is insignificant in the scheme of things, unless you are obsessive about your tyre pressure being spot on.

 

[BentMikey]

Just disconnecting once will release such a small amount of air/pressure that you probably won't see the needle move on the dial at all.
What you need to do, is to disconnect and reconnect the pump 10 times. On the tenth go, see how much the pressure has dropped. Then divided that by 10 to see how much pressure is lost each time. Then figure out how much pressure is added per pump stroke, figure out how that relates to the loss of pressure, and overpump by that amount before removing the pump head.
Is it worth it?







I don't think so!

This won't work, because you do get a more significant release of air when reconnecting. Basically the pump hose all the way back to the pressure gauge gets reinflated by the pressure in the tube. This doesn't happen on disconnection, where the release of air is so small it'll be almost impossible to measure.

 

[asterix]

You need a pump that is built into the wheel; then you would never have to disconnect it. I believe that 'Snotboiler' are working on this idea.

 

[Twenty Inch]

I pump my tyres up to the recommended pressure of 120psi, and am confident that there is no loss of pressure when removing the pump. However two questions are bothering me:

We know that no manufacturing process can turn out entirely identical products, so as batches of tyres are produced, there are differences in the quality of rubber. How do I measure the effect that this has on the tyre pressure?

We also know that heat and cold affects the density of materials, so presumably my tyres are less dense in summer than in winter, which must also have an effect on the pressure.

So my three questions are:

1) how can I measure the combined effects of the two phenomena noted above on my tyre pressure?
2) can I ever be sure that the tyres are running at the correct 120psi?
3) do I need to get a life?

 

[BentMikey]

1) will have no effect on the pressure, since you're pumping to a specific pressure. It might have an effect on tyre volume though.

2) the tyre pressure will only change if the temperature changes after you've pumped it. Perhaps pumping up a warm bike in a warm house and then going out for a ride in the cold might have an effect. I doubt it's much, and I CBA to try and work it out.

3) How's 2" doing? Still the proud dad? We have a new one also, 13 weeks on Saturday.

 

[youngoldbloke]

How does one know that one's pressure gauge is accurate anyway? How can one test it? Is it good practice to have a selection of gauges and average the readings, or is it necessary to purchase an expensive certificated gauge? But how can one be certain of its continued accuracy? What a conundrum!

 

[Twenty Inch]

1) will have no effect on the pressure, since you're pumping to a specific pressure. It might have an effect on tyre volume though.

2) the tyre pressure will only change if the temperature changes after you've pumped it. Perhaps pumping up a warm bike in a warm house and then going out for a ride in the cold might have an effect. I doubt it's much, and I CBA to try and work it out.

3) How's 2" doing? Still the proud dad? We have a new one also, 13 weeks on Saturday.

No, no, you've misunderstood me. Ceteris paribus, the difference in quality of the RUBBER must have an effect on the riding experience. Even if the internal pressure is equal, the changing properties of the rubber tyre that supports my weight and bike.........

.....and so, ad infinitum.

2" is doing great thanks. 14 months old now - trying to play the didgeridoo! How's yours? Settling and sleeping?

 

[Stick on a Giant]

Perhaps what we need is not a pressure guage but a tyre deformation gauge to measure how the tyre will interact with the road.

 

[Twenty Inch]

Perhaps what we need is not a pressure guage but a tyre deformation gauge to measure how the tyre will interact with the road.

Now you're talking. With lasers!

 

[BentMikey]

Doh! Gotcha mate.

miniMikey 2.0 is doing great thanks, almost down to sleeping through the night.

 

[alecstilleyedye]

would a more relevant point not be whether a little less psi makes a difference to most of us?

 

[MartinC]

You could always use solid tyres to save yourself the worry!

The guage isn't the final determinant of what the pressure should be - it's you. From experience you can decide how much air your tyres need for the ride you want. You'll know where this is on your guage - doesn't matter what the absolute value is. So stop worrying about it.