On my mountain bike I have Continental X-King tires (tubeless ready) on tubeless ready rims. I rode them a couple of times with tubes and now I went for tubeless setup with Stan's NoTubes Sealant.

At first everything looked fine, but they keep on deflating slowly. From 3 bar to 1 bar in roughly 10 hours. I've submerged the tires in water to see what's wrong. There are no major cuts or holes, just very small bubbles are leaking through the sidewalls. I did a couple of rides to distribute the sealant inside the tire, I also tried leaving the wheel laying horizontally overnight, but no luck so far.

Is it going to fix by itself after a few more pump-ups, or is the tire bad?

  • 1
    It might just need more sealant to reach the area to actually seal, which may take a few more rides/agitation on your part, assuming you seated the tire properly (e.g. with a compressor, so you get a huge volume of air in quickly).
    – Batman
    Feb 3 '17 at 5:09
  • Yeah, I'll give it a couple more tries. The tire sits well on the rim, even when it deflates.
    – pcv
    Feb 3 '17 at 5:33
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    Is it really leaking through the sidewalls or are you referring to the bead, the area where the tire contacts the rim?
    – mikes
    Feb 3 '17 at 11:10
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    you could try a different sealant or some of the crazy sealant hack techniques, but quite honestly I hate Conti tires for mountain tubeless (yes it's a personal opinion). Myself and several people I know have had endless leaking out the sidewalls, like osmosis out the sides of the tire. Also, mine started showing threads and fraying after just a couple months.
    – Paul
    Feb 3 '17 at 20:06
  • 2
    Are you inflating with air or CO2 or something else? CO2 leaks out of a tyre very quickly.
    – Criggie
    Feb 23 '17 at 19:11

I've found Contis in general to be a bit harder to seal and take up to a few weeks of riding before they settle down. I've tried Mountain King II and XKings both the "Protection" versions I also have friends who have tried this.

Two things that might help

  1. Before fitting wipe the inside of the tyre with Isopropyl Alcohol. The theory is it removes the "release compound" which the sealant might have issues with.
  2. Put lots of sealant in (like 150-200ml) and ride for a couple of weeks. You can then remove the excess sealant if they've settled down (either using a syringe through the valve or by pulling one side off the rim). Riding generally seems to be much better than wheels sitting in the shed for sealing.

I've fitted 3 new Mountain King 2s and an XKing and the last two I fitted seemed to be better using the techniques above. Obviously I've not done an "A/B" test so this is just my experience. My current fix is to buy Maxxis instead which seem to go up no problem.

  • 1
    If sealing indoors you can also give the wheel a spin (at a variety of angles) every few hours to spread out the sealant. I also found higher pressure also helped.
    – Rider_X
    Feb 23 '17 at 17:01
  • This, I had an awful experience with a pair of X/Race Kings RS tires last year, they didn't seal in 3 months, I've used all the tricks, except for Revoseal instead of Stan's.
    – Klaster_1
    Feb 24 '17 at 2:56
  • The answer as above is always more sealant and buy Maxxis EXOs. Some brands require more sealant than others and TR tyres in themselves are lighter and more porous than USTs. USTs can be inflated without sealant at all.
    – DWGKNZ
    Feb 25 '17 at 11:22
  • Contra @DWGKNZ I have had the same problem with Maxxis EXO/TR Ikons.
    – JP May
    Feb 27 '17 at 22:30
  • Obviously anecdotal but I had no issues with Maxxis Ardent EXO. 80ml of sealant and one ride and that was pretty much it for a couple of months (when I topped it up with sealant as I was doing all my tubeless wheels). Feb 28 '17 at 16:35

I've used several sets of tubeless ready Maxxis Ikons with Stan's sealant and they've always leaked slowly through the sidewalls for several weeks before they settle down and hold air long term.

The ultra-light sidewalls needed the latex sealant to seep through and dry to maintain full air-tightness I theorize.


My sidewalks start leaking in my Hodag fat bike tires after they get sufficiently worn that the cords start showing. So far sealant hasn't helped because I think centrifugal forces tend to keep the sealant up against the tread area. I'm going to replace the tires when they get to this stage of their life.

  • 3
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    – Weiwen Ng
    Sep 6 '19 at 13:39

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