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Whenever I cycle in heavy rain with my tubeless tires, what I presume is the sealant seeps out of the rims in a kind of gloopy dark-grey mush. Is there something wrong with the sealant I'm using? Or perhaps compatibility between the tires / sealant / wheel?
I heard a moderately loud pop when when I set up the tires and they appear to be seated correctly.
Using gravelking foldable tubeless ready 35mm tires with Orange Seal sealant.
I don't know what the association would be with rain, but sealant coming from random spots on the rim but not the bead lock area implies a tape problem. If it's happening at the bead itself (the joint between tire and rim), too narrow tape could be a cause.
The loud pop is normal and is a good thing. The first thing to double check would be a consistent lock all the way around.
Orange works well with all the light Panaracer or Panaracer-made tires, so no this does not sound like a compatibility problem.
If you got a puncture (which is potentially likelier in the rain) and some sealant escaped in the process of sealing, you could get something like this, collecting at the rim in a way that suggests that's the leak, but it's not. The same is true if there was a puncture that the sealant wasn't quite able to fill. But that probably wouldn't be both tires, all the time.
Light tires like this can have a way of "eating" a higher amount of sealant in initial riding, and until then can lose some through the casing. It's possible this is what you're seeing. You can test that easily by using a 2mm allen or other small thin tool as a dipstick through the valve, and then re-upping as needed if there's little or no free liquid. Clean the tire off before riding so you have a fresh start. If that doesn't work then I think looking at the tape is probably the next thing, unless you're just losing it from punctures.
From my read of the photograph, I believe this is brake grime, not tubeless sealant. The black color is some mixture of brake pad material and aluminum from the rims and we can see that it extends both towards the middle of the rim and out on to the tire sidewalls. As the brake pads abrade the rim and vice versa, they break off a bunch of small particles. In the rain, this dust rinses off and sticks to the sidewalls and to the rest of the rim, but not so much to the brake track itself, because the pads push most of it off that area. Braking in the rain may cause more of this dust to form because the wet rims and pads are more prone to pick up grit.
I’ve seen a number of bikes with the same dirtiness with clinchers and tubes, no tubeless sealant required. The worst/most visible cases tend to be the ones with white paint, aluminum rims, rim brakes, and fenders. Whether that’s because bikes with fenders get ridden in the rain more, or because the fenders direct the brake grime slurry back to the fork legs, frame stays, etc., I’m not sure, but I suspect it’s a combination of factors.
TL;DR: I think that’s just brake dust, no indication to worry about the tubeless setup
I would presume that you are using some bad sealant which might be water-soluble, I don't really know but that is the only connection I can make between water and leaks. Also maybe your sealant is old (you should change it every 6-9 months).
