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How to inflate tyres accurately?

madstermadster Posts: 5
edited May 2017 in The workshop
Hello,

I'm relatively new to commuting, and one of the basic rules I learned is to always inflate your tyres.

Now, I find this very challenging, because every time I inflate tyres there is always a split second of air coming out, when you remove the pump and screw the cap back in. I have no idea how much pressure my tyre eventually has. Sometimes I even doubt is better than before :/

Am I doing something wrong? How do you inflate your tyres?

Thank you!

Posts

  • slowbikeslowbike Posts: 8,490
    I put in a couple of PSI more than I want - so when the pump head doesn't release quickly it comes back down to the pressure I need.

    But TBH - it's irrelevant - unless you spill air for a few seconds you're going to be within 5psi anyway.
  • fat daddyfat daddy Posts: 2,632
    air always comes out, so just choose a number and pump it up to that .... if you decide it needs more or less air then next time pump it up more or less.

    Thinking I need exactly 90psi and trying to inflate to 92.3psi so when you de couple it deflates to 90psi +/- 0.4psi is futile and pointless

    keep the process simple, pick your arbitrary number in the range on the tyre (90psi), take the pump off "pssht" and test the tyre ... if its not hard enough for you ... stick more in .. (95psi)
  • slowbikeslowbike Posts: 8,490
    fat daddy wrote:
    air always comes out, so just choose a number and pump it up to that .... if you decide it needs more or less air then next time pump it up more or less.

    Thinking I need exactly 90psi and trying to inflate to 92.3psi so when you de couple it deflates to 90psi +/- 0.4psi is futile and pointless

    keep the process simple, pick your arbitrary number in the range on the tyre (90psi), take the pump off "pssht" and test the tyre ... if its not hard enough for you ... stick more in .. (95psi)

    exactly - my arbitrary number is "just above" the magic number I think I want - as my guage isn't calibrated it may or may not be the pressure I get ... seems to work though :)
  • timothywtimothyw Posts: 2,482
    The thing you have to remember, when you are pumping up tyres you are not just inflating the inner tube/tyre - you are also bringing the air inside the pump's hose up to that level of air pressure.

    The consequence of this is that there will always be a 'hiss' of air when you disconnect the pump, as the air pressure inside the hose returns to the ambient air pressure - and although it will take a fraction of a second for the inner tube valve to seal, you're unlikely to loose any noticeable amount of pressure in that time.

    Well, unless you make a real hash of removing the pump anyway!

    So in short, don't worry about it.
  • fenixfenix Posts: 5,437
    timothyw wrote:

    So in short, don't worry about it.

    This.
  • The RookieThe Rookie Posts: 27,747
    A ten degree temperature rise using the day will see a pressure change of more than 3% anyway!

    Where I was riding recently was seeing a 30C rise from 5C overnight to 35C at 2pm....so about 10% pressure effect.
  • cooldadcooldad Posts: 32,904
    I still use the thumb test.
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  • madstermadster Posts: 5
    Thanks guys, I thought there was some special method I didn't know... all good then :)
  • drlodgedrlodge Posts: 4,824
    As TimothyW said, the hiss of air being expelled is air from the pump tube, not from the tyre. Just inflate to the required pressure (give or take) and be done.
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