I've had good and bad experiences with both slime and ultraseal. The issue seems to be a mixture of cure time and hole size. If the hole is small a small number of rubber bits block it, it cures quickly and you have a near permanant fix. If you get a big hole you get the "tea leaves in the sink" effect and get to do a proper fix after your next meal break. If you get a hole in a surface that moves or isn't flat (seam of a tube in my case) it simply doesn't work and the stuff is just messy. All in all though I can see practical advantages to this. I don't carry it as the Bonneville has very easy to change tubes, but for example with my dad's Guzzi running tubeless tyres on the worlds tightest tube type rims, Ultraseal would for sure be my first choice if he ever went more than a hundred miles from home.

Like I said, it's the engineer in me that likes to see proper testing, an affliction that no doubt does prevent progress that inventive people will naturally bypass. I've had one explosive blow out in my previous test driving career (I used to work for WABCO the brakes people), fortunately on an axle with twin tyres but the noise was enough. I can also change my tubes in next to no time, so no encouragment there I guess

The comments from the guys doing this in the US are interesting. The bigger the wheel the harder it is to seal, or is it the front position? The spoke flexing is different either way IMHO. A rear is going to flex it's spokes based mostly on engine torque applied? The ends of the spokes to me will "roll" in the rim, something the front also see's under braking? The front is subject more to impact type hits to the rim trying to push the spoke into the rim, making a gap a little like a poppet valve as the rim flexes? The longer the spoke the bigger the gap created when it moves, so the harder it is to keep your chosen seal in compression?

As a test routine, I'd want to seal the biggest rear I could and ride it off road so it see's impacts. Then I'd want to try the same size as a front, so 19-inch on a classic/Enfield? You'd at least be learning if it's the wheel loading or spoke length that limits your seal. Hopefully you find out if you've got a rolling or opening issue and can then add a suitable o-ring or flat seal to support the semi-liquid?

My other fear is changing the resonant frequency of the wheel by some stiffening of the rim to spoke joint. What's the chance of breaking a spoke now and after the seal starts acting as a damper? If a spoke breaks what are the chances of this causing a rapid tyre failure? Like I say, it's just the engineer in me that likes to see FMEA's and the like on safety critical items.

Good luck to the innovators out there

Andy