Tubeless has started slowly losing pressure

Nick Payne
Nick Payne Posts: 288
edited October 2017 in MTB workshop & tech
I have a pair of Compass 650bx48 Switchback Hill tyres mounted tubeless on DT Swiss XM 1501 wheels. I use them mainly for gravel road / fire trail touring. For the first couple of months, both tyres held pressure without any problem, but lately the front tyre is losing about 10psi/day from the 25psi that I normally run it at. Since this started happening I have replaced the valve core and added another 50ml of sealant (Orange Seal) to the tyre, but neither change made any difference to the problem. I can't see any evidence of damage to the tyre anywhere or of sealant leaking. Any suggestions on what else I should look at?

The rear tyre still maintains pressure fine - I just check the pressure every ten days or so - but I have to pump the front back to pressure every time I take the bike for a ride, and the following morning it will have dropped by 10psi or so.

Comments

  • The Rookie
    The Rookie Posts: 27,812
    So just pump it up before the ride!

    Sometimes they hold 100%, sometimes they don't.
    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.
  • iwilldoit
    iwilldoit Posts: 710
    What tape did you use to seal the spoke holes, I had a similar problem and the tape had come a little loose in one small place and it leaked into the rim, I've got a big water butt by my shed and put the wheel in it and at around 40 psi you could see bubbles coming out around some spoke holes and the valve.
    https://goingdownhillfastsite.wordpress.com/
  • Nick Payne
    Nick Payne Posts: 288
    After a bit more investigation I found that the sidewalls had very slow leaks at a couple of the locations where the moulding process leaves small knobs of rubber sticking out from the side of the tyre, and the normal process of riding the bike was not letting the sealant get to these points to seal them. I took the wheel out of the frame and sloshed it around horizontally to coat the sidewalls with sealant, and this appears to have sealed the leaks, as the tyre is now holding pressure.
  • JGTR
    JGTR Posts: 1,404
    Nick Payne wrote:
    After a bit more investigation I found that the sidewalls had very slow leaks at a couple of the locations where the moulding process leaves small knobs of rubber sticking out from the side of the tyre, and the normal process of riding the bike was not letting the sealant get to these points to seal them. I took the wheel out of the frame and sloshed it around horizontally to coat the sidewalls with sealant, and this appears to have sealed the leaks, as the tyre is now holding pressure.

    You need to slosh! Give wheel good shake/slosh when fitting new tyres to get sealant to everywhere.

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