I bought a Cannondale Fat Caad 2 that came with tubeless ready rims and tires— the rim is even pre-taped. I’m converting to tubeless currently — removed tube, installed valve stem, put 120ml of sealant in the tire, inflated the tire to 30 psi to seat it, rolling the tire.

Testing with soapy water, it’s sealed everywhere except for at the rim seam. It’s actually leaking through the seam at the groove where the small bubbles in the picture are and slightly at the bead where the big bubbles are.

Will this seal after rolling the tires for a few days or should I open it back up to do something, and if so, what?

  • 5
    Looks to me like you have a bad rim joint. If more sealant (maybe some heavier duty stuff) doesn't fix it then you need either a new rim or a tube. You might try letting most (but not all) of the air out of the tire, then laying it down with that section down overnight, so more glop collects there and it has a chance to "set". Mar 19, 2019 at 1:42
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    Did you slosh the sealant around so it can seal the rim seam. You want to coat the whole internal rim/tire complex so that any small leaks are sealed. For example I often get a leak near the valve stem / rim interface. As soon as I slosh the sealant around near the stem I can instantly hear the leak getting sealed.
    – Rider_X
    Mar 19, 2019 at 14:20
  • @Rider_X - I did do that, but I realized at 4am that I still had the psi up to 30 to seat the bead. I let it out down to 15 til I got up later when I lowered it to 5. Rode it 18 miles on railroad gravel today and it seems fine. Not sure if it needed time for everything to solidify or if the higher pressure was keeping it from sealing. I'll keep an eye on it.
    – MikeJansen
    Mar 19, 2019 at 18:38
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    @MikeJansen some times it can take some time at low pressure for the seal to “cure” before it holds for higher pressures.
    – Rider_X
    Mar 19, 2019 at 20:27
  • Is there a burr or a "step" at the rim joint? If so, perhaps filing the rim joint down to make it flush may help the tire seal better.
    – P. Barney
    Mar 20, 2019 at 3:22

2 Answers 2


The fix ended up being very simple. After inflating the tire to 30 psi to seat it, I decreased the psi to 15 and rolled the tires like normal over the next couple hours. Then I dropped the psi down to my running pressure of 5 psi.

The problem simply seemed to be that 30 psi was too high while the sealant was sealing the gaps. 15 psi seemed high enough to push it into the gaps and low enough to let it seal.

  • 1
    Thanks a lot for adding your own answer! I wish you good rides with the tubeless tyres.
    – gschenk
    Sep 18, 2019 at 20:14

The only solution that I've found for this is to put in a thicker sealant along with the one that you're already using. The two that I've had the most success with are Finish Line and Never Flat. I've never had an issue mixing this with any of the sealants that I've used before.

If this doesn't fix it, then unfortunately it's just a matter of not using that particular rim/tyre combination. Some tyres just don't play nicely with some rims and there's no way to make it work.

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