How to inflate tyres accurately?

madster
madster 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!

Comments

  • slowbike
    slowbike Posts: 8,498
    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 daddy
    fat daddy Posts: 2,605
    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)
  • slowbike
    slowbike Posts: 8,498
    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 :)
  • timothyw
    timothyw 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.
  • fenix
    fenix Posts: 5,437
    TimothyW wrote:

    So in short, don't worry about it.

    This.
  • The Rookie
    The Rookie Posts: 27,812
    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.
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • cooldad
    cooldad Posts: 32,599
    I still use the thumb test.
    I don't do smileys.

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  • madster
    madster Posts: 5
    Thanks guys, I thought there was some special method I didn't know... all good then :)
  • drlodge
    drlodge Posts: 4,826
    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.
    WyndyMilla Massive Attack | Rourke 953 | Condor Italia 531 Pro | Boardman CX Pro | DT Swiss RR440 Tubeless Wheels
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