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Leaky tires but no puncture?

Discussion in 'General Motorcycling Discussion' started by Exportswede, May 23, 2016.

  1. So I have a 2008 CB400 that I love very much.
    No problems with it so far, never had anything wrong with the bike, no punctures, no cracks, no...nothing with the tyres, yet, for the past few weeks, whenever I go check my tyre pressure in the morning, it's dropped a fair few psi.
    Over a week, it used to go down 2-3 psi (which feels pretty normal) but in the past 2 weeks, it's started dropping 7-8, even 10, usually only on the rear, but sometimes on the front too.

    Friend suggested it might simply be someone sneaking around deflating my tyres, but I don't see why they would nor do I see when or how they'd do it, considering where I park every night. I've checked multiple times, and there are no cracks, no punctures, nothing stuck anywhere and there's no visible leaks coming from anywhere (spraying water all over the tyres, nothing shows up anyway).

    So, what gives? Anyone have any ideas? I've checked at home, with my own gauge, I've taken it to three different petrol stations to check, all with the same results. It's starting to get a bit frustrating.

    Oh, I've got a fairly new set of Pilot 4s (my second pair, as they've worked perfectly so far) and as I said, never had any issues in the past.
  2. Might need new valves...
    • Agree Agree x 2
  3. If not the valves there may be minor corrosion between the tyre & rim preventing it from sitting 'flush'.
  4. this one

    make up a solution of soapy water and pour it over your valves and check for bubbles forming, it's odd though that it would be affecting both valves at the same time but I think Steve VtecSteve Vtec is correct - unless the batch of tyres is faulty, could always phone the fitting place and ask if they've had similar feedback.

    last thing, are you checking the tyre pressure when warm then again in the morning when they are cold? this will make a difference as pressure is higher in warm tyres due to expansion.
  5. Inflate, maybe even over-inflate a few psi. Put a dab of saliva on the open valve and observe closely over a few minutes - if it is the valve, the bubble will grow. - replace the valve.

    A friend of mine who operates a tyre business told me that it is actually the cap which holds the air in the tyre most securely. That the valve is only there to stop it rushing out when inflating. He suggested that all valves should have metal caps with a little rubber gasket seal in them. That was news to me, but I accept he probably knows more about it than I do.

    The other, very real possibility is that you have a poor seal around the bead of the tyre. The solution is to remount the tyre. In extreme cases, it may be possible to find the leak (where it is significant) by rolling the tyre into a pool of water and looking for bubbles around the rim. You won't be seeing bubbles if it is only leaking at the rate of a couple of psi per week or two however.

    What you've tried with the water may work, but you are much more likely to see leaks if you use very soapy water so that it will form and hold bubbles that you can see. Don't forget to clean the soapy water off the tyre thoroughly before riding.

    Explore the simple things first. Most tyres will lose a little air over weeks - a couple of psi only. I don't find this more than a good practical reminder to check tyre pressures frequently. It's not a bad idea to carry a tyre gauge and check the pressures every tank or two or weekly as a minimum. With the onset of cooler weather, tyres which do not leak air will lose pressure, not due to leakage, but to change in temperature. Why you should always check pressures when the tyres are cold.
    • Agree Agree x 2
  6. Thinking the same. Might need to get that sorted, because it's tarting to really piss me off.
    Thanks for the input! Always appreciated to get someone else's opinion before you go off and try to fix stuff :)
  7. Yeah, I always do pressure checks when the tyres are cold. Leave the bike overnight, and check first thing in the morning, as I have a gauge with me on every ride (next to my bike toolkit, neatly fitted under the seat). Just seems odd that it's started only in the past two weeks, as I've had the tyres for a few months and they've never had any issues so far. Hence, I'm thinking it can't be the actual tyres (as in manufacturer fault or possibly a poor seal). Again, losing a psi or two over a week, that's not even an issue, that's just what happens, but when we're talking 5-6psi overnight, then it's starting to get problematic.
    Might try to soapy water thing though, and see what happens :)
  8. Slow leak is generally not a puncture so maybe just stop in at the tire shop and see if they have 5 mins to check for you. Watered down morning fresh bubbles like crazy, great for finding leaks. As jstava said, please please clean the tire properly after doing this. Morning fresh is v slippery
    • Agree Agree x 1
  9. A mate forgot to put his metal valve cap on at a track day, turn 1 at Eastern Creek and he had a front tyre deflate, centrifugal force opened the valve.Lots of damage to Anton's Guzzi race bike. I had heard this lots of years ago but this was the first time I had heard of it happening to someone I know.
    • Informative Informative x 2
  10. Slippery tyres = bad idea. :D

    Yeah, will definitely go get it looked at.
    Thanks a lot Steve VtecSteve Vtec, jstavajstava , chilliman64chilliman64 and Big WBig W for all your input. This is why I like NR so much :)
  11. Thats why angled tyre valves are a must for high speed stuff
  12. Some of us actually have to wash our tyres when cleaning the bike, because we are sloppy with the kero/chain muck/oil. Detergent is fine when rinsed properly.
  13. Check that the valve core is done up tight too.
    • Agree Agree x 2
  14. Do you have a 90 degree valve stem with a rubber base.
    If you do, there's a chance that the rubber base is split. This is sealed when the wheel is stationary, but when the wheel is spinning it starts to let air out, the faster you go the quicker the air escapes.

    My Valkyrie had these, the front tyre deflated at high speed, it was very interesting to bring the beast to a stop.
    • Informative Informative x 4
    • Agree Agree x 1
  15. Yeah, that might be it actually. Seeing how it's fine when left overnight (well, as fine as can be) but then air keeps seeping out when riding. Will get it looked at today so hopefully this'll be the last of it :)
  16. Ha, I'm the same. Whenever I clean the chain, my bike needs a proper wash afterwards too. I'm too messy, apparently :D
  17. I've heard only bad about the angled valves mate. Been told ok for the road not ok for the track as they have high failure rates.
  18. At EC the other month they were handing out metal caps to anyone who didn't have them at scrutineering time, and brought the subject up at the riders meeting.
    • Informative Informative x 2
  19. Mine are rated up to 350kph which should safely have my pace covered! The standard vertical valves can apparently be forced open due to centrifugal force at high speed, which is why they recommend at least using metal caps with the secondary seal in them.
    • Informative Informative x 2
  20. Might not be the cause, but I had similar symptoms. Rear had a slow leak, needed a few PSI every fortnight or so. Front never dropped. Then rear started getting worse until would go dead flat over weekend. Was corrosion on Alloy rim.

    And you bunch or rotten sods! Was very happy with my angled valve stems until now. Rubber base does seem to be very flexible.