Sweaty tires: why is sealant leaking from the sidewalls?

I got a new-to-me mountain bike this January, and it is great. However, I noticed that sealant is sweating out of the sidewalls.

The tires are set up tubeless on Stans NoTubes Arch wheels with S-Works tires on the rear. The tires might be a bit older, but they still have quite a bit of tread on them. I have new ones, so changing them won’t be a big deal either.

What is causing this? What should I do? Should I replace the sealant? Or the tires and the sealant?

shake em around until it stops. the sidewalls are just thin. Probably will need a top up at some point.

Mine kept seeping occasionally for a couple months

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Thats normal, it’s the difference between a tubeless and tubeless-ready tire. It will settle once the sealant dries up and seals the sidewall for good. I haven’t experienced it on MTB, but my Schwalbe Pro One TT skinwall were leaking like a colander.

Depending on the amount of leakage consider topping up the sealant more frequently.

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You are probably good, some weeping is normal from a lot of tyres, even though that generation of Spec tyres where alle 2Bliss (tubeless), so it should not weep that much.
I have used Fast Traks from that generation with all casings and never experienced weeping.
What sealant?

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Super common, my MAXXIS MTB tyres do it all the time, all models, all TR.

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I’m not sure, the sealant was put in by the previous owner. I bought my own (I think Orange Seal, but I am not 100 % sure). I reckon it’d be advisable to clean out all the old sealant first? (As you might be able to tell, I’ve only been on the tubeless train since last year when I bought my new road bike. But I have yet to do any maintenance in that regard.)

Some tires just do this especially Schwalbe tires. I have a pair of Schwalbe Rocket ron’s which I have on my daily commuter which have wept for 3 years now with rarely topping up

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That’s not bad & you’ll be fine. I’ve been tubeless since 2008 or so & have seen this in many many tires. I’d say the worst were Bruce Gordon Rock & Road by Panaracer. To be fair, they weren’t tubeless rated & I was using a homemade tubeless brew. Many different Maxxis models have done it for me but my recent Forekasters with Orange Seal Endurance don’t seem to weep much at all.

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I have never used orange, just Stans. Anyway, by all marks youre good to use that tire.

I never clean out old sealant completely. I just remove clots and lumps and other loose items.
When adding new sealant some of this sealant will be “used” to cover the inside of the tire anyway.
EDIT: But if you change to another type of sealant I would have removed as much as I can.

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IIRC S-works tires have a 15% thinner sidewall as a way to save weight, or at least they did on the XC tires and mine would weep like that. Take the wheels off and lay them on their side over night and it may help coat the tire.

You will probably want to add more sealant after doing that. If the sidewalls are leaking sealant it means air is getting in and will be drying out the sealant and you may be left with mainly water after the good stuff in the sealant dries out. . I would add some more sealant after the tires have a nice coating.

Change it. The sealant can separate over time, the sealing stuff you want dries up, and the rest seeps out. (Well maybe not all of it). It then doesn’t work well anymore. I’ve mostly had this seeping issue when the sealant got old (ie, when the wheels hadn’t been used for a few months).

When you change it, just wash/wipe out all the old sealant and any big lumps etc. I wouldn’t make any more effort in removing the old sticky sealant, because a), its a massive pain, and b), you’ll be opening all the pricks and cuts up that its currently sealing. There are some sealants that aren’t very compatible, but I think the majority is fine, and even the other ones are ok once dried. So I’d just get rid of the liquid stuff and put new sealant in.

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