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Question on tyre pressure

Discussion in 'Maintenance and Servicing' started by MrShadow, Aug 29, 2014.

  1. My problem is I have to ride to get somewhere I can adjust tyre pressures. By this time, the tyre has warmed up. And as we all know, tyre pressures should be measured when cold. I can't spring for an air compressor at home (maybe if I hadn't gone for the Triumph... damn them for making such an addictive bike!).

    So my question is this: Say I measure the pressure when cold and it is 2 psi off (33 instead of 35 for example). By the time I get to the service station, for example it may read 35 psi (an increase of 2 psi). Would I be correct in assuming the correct psi would now be 37 psi to bring the tyres up to the correct pressure?
  2. Just set at the servo and don't worry about it, not like you're track racing. A compressor is nice to have though and you can pick one up these days for under $50 I would think.
    • Agree Agree x 1
  3. That's what I've always done - just curious :)
  4. Its a valid question, and logically your tyre pressures will change throughout the remainder of the ride depending on amount of highway, corners, surface condition, amount of braking, ambient temp, wind cooling factor, mass change for food/toilet breaks, and changes through out the day for each etc. So following on from that, you should probably consider adjusting your tyre pressures throughout the course of the ride for optimum connection, ideally every 8.5-8.6mins I'd say. Jk man, get a gauge, it will no doubt be inaccurate, but at least you can hope its consistent.
  5. We have a compressor now (super handy!) but I used to just add an extra 2psi in when I filled up my tyres in the past.

  6. They take forever. Plus all the fart-arsing about connecting to a battery and you'd have to run the motor so as not to flatten the battery.

    I've got a similar one for inflation in case of a puncture which I carry with me, but to top off your tyres before a ride a half dozen pumps and you're done.
  7. I just use a foot pump for adjusting up a couple PSI - which is about all you need in day to day riding.
    • Agree Agree x 2
  8. Treat tyre pressures as advisory. You can safely move up to 5psi either side, provided it doesn't upset the handling of your bike. Although you risk more punctures on the low side.

    I've always played with mine to optimise the response of the bike. I used to run about 40psi on the rear of the 955, but 36 on the front.
  9. Another thought as an alternative is just to have a hand gauge at home. Check your pressures there - you may not need to worry about pumping at all.

    I bought one, and hardly have to worry about stopping at the servo now (except for Gas - no one has a solution for me there yet :) )

    If you do have to pump it up (say they are 5psi down), you can check the pressure again by the time you ride to the servo. While not exact science you can gauge the difference there, and it might give you an idea how much extra you need to pump in.

    ie: If it's 28psi at home, and it's 31psi at the servo and you know you need 33psi cold, pump it up to 36?
  10. one of these has a gauge on it. not expensive.
    front tyre of a motorcycle doesn't have much more air (has less?) than a mountain bike tyre, and similar pressures..

    servo air pumps can be really shit for accuracy..
    my local pumps in 33psi when I set it to 43psi (it's a Shell digital one).. shit...
    • Like Like x 1
  11. The street triple has 34 front and 42 rear PSI. I'm happy to use the servo - though the exercise would probably do me good :) I do have a pressure gauge at home - was just curious as to whether tyre heating and associated pressure increases were linear.
  12. Practically, yes since most of the gauges aren't accurate enough.

    Let me explain a bit.

    33psi cold to 35 hot is an increase of pressure by ~6%.

    So to set it to 35 cold, it will need to be 35+6% hot, which is 37.1psi.

    So for all the practical purposes you're correct since 0.1psi is negligible and not worth worrying about.

    Generally you can expect up to 10% increase in pressure (depending on multiple factors).
    But if it's the same servo you go every time you can measure the increase a few times to have consistent number (like 6%) and always use it in the future.

    Note that it will change in winter, summer, rain shine, but again will probably be negligible.

    Another note. If you need to pump it up much more than a few psis then I would recommend rechecking the difference because the error margin can accumulate up to a few psi-s.

    Hope that helps.
    • Like Like x 1
  13. +1 for bicycle pumps. I keep a floor pump in the garage and a hand one in my backpack (along with the puncture repair kit), both with gauges.

    It's just convenient to do it at home where the tyres are cold and there's never a line for the pump. Short of a puncture, it doesn't take any more than 3-4 strokes of the floor pump to get my rear up to spec. I even do the tyres on the cage while I'm there.
    • Agree Agree x 3
  14. but don't trust the gauge on the pump in #12 either. up to 50% out. get a good one of those slide type gauges from a auto parts store. They are small and light enough to carry on a bike.
  15. Servo machines give me different readings, so I bought a cheap gauge, and used my bicycle pump (like #11) which also has a gauge but doesn't work on the ninja for some reason.
    The cheapo gauge has been giving me consistent readings (minor drop over the course of a week of commute) every morning.

    Now I only check it weekly, unless something different happened the previous day.
  16. Just FYI, pencil style gauge was on sale at Supercheap Auto for something like $3.
  17. I already have a small pressure gauge, though the pencil one might be handy for rides if you get a slow leak or something.
  18. I use one of those as well and it works a treat
  19. That's exactly what I use on a Honda CBR900RR and it's easy to uses on the front. I check tyre pressures with a PCL guage I've had for 30 years, I hope it's still accurate, although I don't race.

    I initially bought it for my bicycle and found it worked perfectly on the Honda. Cheaper at online cycle stores like Wiggle or Ribble but usually about $40 at your local bicycle shop.