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Flat Tyres

Discussion in 'Technical and Troubleshooting Torque' started by gato, Sep 9, 2009.

  1. Hi all,

    Over the past 2 weeks my bike tyres have been deflating on their own - rear more than front. I don't have the numbers but it was noticeable enough when riding, especially pushing it around to park. The difference after pumping them up again was like gaining 100kW and losing 200kg.

    I pumped both tyres up to 250kPa as specified on saturday. Today morning i had to pump them up again. they were around 230+kPA (first reading on pump). What could be the problem?

    I checked for any obvious puncture marks and found nothing. I appreciate all help and advise, thanks.
  2. Check that the valves are not leaking....
  3. Could be a number of things mate, how old are your tyres?

  4. tyres are 2 1/2 years thereabouts.

    how do i check the valves besides getting a shop to do it during tyre change? do i just listen to hissing noise?
  5. It might be time for some new tyres me thinks bud.
    Definitely get yourself to a tyre shop and have a professional tyre fitter have a look at them. My money is on them being hard and cracked (but i could be wrong)

    Rubber is porous material and it's not unusual for some air to escape through it. It's a good practice for all riders to check their pressures regularly. However with the amount of pressure loss your talking about, it sounds like your tyres are shot.

    2 1/2 years is a long lifespan for a tyre that hasn't been stored and kept out of the elements.
  6. Easy way to check valves, put a bit of spit on them, if they bubble, they are leaking....
  7. Oh and i never answered your actual question.

    Check for valve leaks with a bit of soapy water. The rubber around the valve deteriates over time. Valves need to be replaced at regular intervals and are usually ignored by tyre shops. :roll:

    What's more likely to be a problem though is the spring inside the valve no longer being springy enough to keep the valve closed while you're riding. Can't really check for it either, except your tyres go down everytime you go for a ride. The inner valves can be changed independantly of the valve body, and if you have the right tool (costs $8) you can do it yourself.
  8. Can you tell me where to get tires that last 2/12 years :LOL:

    Are you checking the cold pressures?

    Not sure what your bike is but 250kpa (36psi) is to low on the Bandit and an extra 6psi makes a huge difference.

    Put some spit on your finger and put that on the valve to check for a slow forming bubble.
  9. Thanks for the excellent advice and information. I had the feeling it was about time for tyre change. I'm going to do some research now for the best shops. Anyone has any recommendations? I'm riding a GSXR600 K6 by the way.
  10. They're actually the stock tyres that came with the bike! :eek:
    How long does a set of tyres last in general? of course, that would depend on the riding style.

    I always check them cold - after a 2min ride to the servo. The suzuki manual specifies 250kPa. this morning i put them up to 255kPa. i'll keep monitoring while I decide on which shop to go.
  11. Which area do you live in?

    And yeah i agree with 2wheels, making your tyres last for 2 1/2 years on a gixxer is not koshar!!!! more trackdays for you i think.

  12. :grin:

    It's sacrilegious to treat a gixxer as a commuter, a pack mule! Need to go for fun rides more. Yeah i've been wanting to do california superbike, but time and especially money does not permit at the moment.

    I live in the richmond area. Moving down to the Blackburn area soon. So in terms of shops, I'm flexible and open to all good suggestions. For a good shop, I will literally go the extra mile!
  13. There's Everything two wheels in North Fitzroy, Pete's got an excellent reputation.

    These guys are further out east near Mt.Waverley. I can vouch for these folk.

    If you go and see them, have a chat about joining in on their next trackday. With their group bookings they can get the price down as low $120, plus they'll give you lots of good pointers for free. So if SBKschool is out of reach at the moment, this is a good option.
  14. Kenoaf. Go see Pete. And tell him I accidentally f*cked his mum again.
  15. Porous? Are you sure and to what extent? I never would have believed that statement but this link here says there's diffusivity which means there is some permeability. For the time spans we're talking about here, the permeability of a tyre to air is near enough to negligible for practical purposes as far as I'm concerned. Porosity of rubber is not the issue. Holes could be.

    My last bike was a shocker with the front tyre. I had to pump it up every week. In two weeks it would go from about 30 psi to about 20. I only had to pump up the rear tyre once in 8 months (and that was to add 4 psi when the weather cooled).

    My car tyres are great. They lose a maximum of 1 psi (with similar weather, but usually little-to-no change for at least 3 tyres) in the space of 2 months and that's been the trend for the last 2.5 years.

    My guess for the OP is that the rim or the valve is the issue.

    EDIT: Just a follow up on permeability for anyone who is interested, if I can believe this link then 2.1 x 10-6 m/day is air going through rubber which means it'd take at least 13 years for the air to start leaking through the rubber (say it is 1cm thick) at an extremely miniscule rate.
  16. Yep. Not all tyres do it, not all tyres do it to the same degree, but it does happen all the same. It's exacerbated when tyres are run up to the higher temp ranges. The pressures go up with them, which lets more air out, and once everything's had a chance to cool, you end up with lower pressures than when you started.

    Old cracked hardened tyres can open up pores and release the air as well. Interesting thing is, they don't usually go completely flat. Once the pressure is low enough the pores close up and they stop doing it. So what you end up with is a half flat tyre, no obvious puncture, and a bald spot where you've been scratching your head.

    It was actually taught to me by FLUX, i wasn't in the habit of checking pressures regularly, but once he put me onto it, I was shown that the pressures end up all over the shop. So now before i go for a blat i check them. :wink:
  17. I said cold not warm.
    Seriously get one of these or similar and check them at home.
  18. WTF? what's going on there???
  19. Gotcha. I'll get one of those tyre pressure gauge this weekend. thanks for that 2wheelsagain.

    seriously, i dreamt about buying an air pump last night. the joys of inflating my own tyres in the comfort of my own home.
  20. Make sure you don't buy a cheap and nasty one. I know a bloke who had the handle break off while he was using one, and the shaft shot out and very nearly embedded itself in his eye.