Homemade Tubeless Tires As I was browsing Youtube for cycling related videos, this one on making your own tubeless setup caught my eye.

The procedure is essentially as follows:


Clean a standard rim (not for tubeless tires, which has rimtape installed)
Fit a 20" tube on a 29" wheel
Split the tube along the seam of the tube so that it covers the edges of the rim
Clean the chalk (used for manufacturing the tube so it doesn't stick to itself) out of the tube
Install a standard tire (designed for tubes) on top of the split tube (so the edges of the split tube cover the rim), and pump it up to see if it seals well enough
Add sealant and shake the tire up as usual, trim the excess 20" tube off the rim.


I can see why this works to some extent [ the tube prevents air escaping through the edges of the rim as well as towards the spokes ], but I am curious about a few aspects of this:


Why doesn't air escape through the standard tire? Presumably the tire itself is somewhat porous to keep the weight down (since only the tube needs to be air tight but the tire itself does not). I'd also guess the tube on tire contact isn't very good at low pressure, but the pressure may be high enough and the interface between the tube and tire nice enough.
Why does the tire not roll over the rim at mountain biking pressures? Presumably theres less area and mechanism for the tire to grip onto the rim, and I'd expect a sew-up tire-like roll off, especially on rough terrain, or at least the seal to give out.


Now, I'm not recommending anyone try this (including myself), but it does seem like some people have used this successfully. In the unlikely event that someone has actually tried a setup like this, I'm somewhat curious as to what the results were as well (but I'm not trying to primarily solicit opinion-based answers).
Air will escape, one of the biggest problems with Ghetto tubeless (unfortunate, but long established name for this technique) and not using specific tubeless ready or UST (tubeless standard) tires is that you need to inflate your tires a lot. At worst for every ride.
The tires often do roll off the rim. Not every combination of Ghetto tubeless will work (the internet used to be full of lists) so it's about trial and error. It's always been recommended to do the rear first and ride for a few rides before doing the front. If the rear tire comes off you may be able to stay up right!


Higher pressures (+40 psi) are worse for tires rolling off.