M41 has recently released a 20x4 muni with brake…
Sounds like a fun toy
Finally!! Yesterday my lbs called and told me that they got the tire now! I have had other parts for this project for ages now so I got straight into building the wheel yesterday evening (got nipples from lbs too because my spokes were missing them…).
One thing to note when ordering rims from Classic Cycle is that their erd measurement has spoke hole offset taken into account already. I guessed the offset for my calculations when ordering spokes and they were just a little too short to use with 3 cross lacing. That’s why this wheel is laced 2 cross now.
I bought a regular 20" tube for testing purposes today. No tubeless yet because I had just ran out of tubeless sealant and I have ordered more already. Seems to work very well. Tire is a little thinner where the valve is but at least I didn’t notice that when riding in snow.
Frame that I used for testing is the one I normally use for freewheeling. I will build a properly fitting frame when I have time. 29x3 tire looks huge when compared to 20x4! 
I will report when I get more riding done with this thing or something new happens to it. Has anyone else ridden this tire in snow? I’m not sure if I’m dreaming but it felt really good and grippy to me. 
Pictures here: https://imgur.com/a/1CXOA (tell me if that link doesn’t work)
That looks like loads of bouncy fun.