Ive just got a set of UST wheels and thought I'd try my luck at fitting a set of non-UST racing ralphs, so, just for the fun of it and not expecting it to work at all…..
Fitted tyres (no sealant)
Pumped up with track pump (80 PSI until bead was making popping noise)

to my amazement the only leaks are from puncture holes, no audible leaks from sidewalls, etc, and I reckon with a bit of stans in they'd seal fine.

Has anyone one this, what are the downsides/risks (will tyre roll off rim or burp easier), tyres are fairly new with loads of tread, so I dont really want to get rid and buy UST's just yet…

Also, those using Stans, how often have you needed to top it up?

i never would have done it but after some discussions on here i went ahead, with no issues.

provided they are pumped up to a reasonable pressure they should be fine.

i top my sealant up every 2 or 3 months.

I did it briefly as a test on mine (nevegals on traversees), worked a charm once the existing punctures sealed up (I was using some old ultraseal I had in the garage, not proper bike sealant, still did the job). And even with the standard beads, it wasn't going anywhere, it was a pain in the nuts to remove in fact. I'm sure different tyres will act differently mind.

Yeah, the tyres were fairly straight forward to get off after I initially fitted them, which made me think they may be liable to rolling off…. I dont really trust the sidewwalls and general strength of the ralphs after I ripped great big hole in one that was only a few days old, but I must have hit something pretty sharp as the current ons have been fine over al sorts of terain.

Biggest downside I can see is that they are not UST tyres. Ie. they are flimsy and will puncture and probably pop out of the rims if you hit something hard.
USTs are designed to be run with no tubes and no sealant (although most people do use it) and are therefore meaty, tough and resiliant, with very thick sidewalls.
I've got plenty of non-usts hanging on the garage wall, but will never risk running them tubeless!

I've done exactly what you describe and this was the outcome.

yes it works, but there are limitations. 1) puncture prone and 2) frequent burp of air when riding low pressures (25 to 30psi – 12stone rider)

the best fix to these that I've found is a) fit a stans rim strip (or cut down inner tube approach that many like to do) in order to make a tight seal under the beading and b) use some wheel milk to ensure thorn punctures are delt with automaticaly.

I was thinking a bit of rim tape or standard rim strips would make the tyre a tighter fit, I was thinking that non-UST's would also be much lighter..

Duckers – yes rim strip or rim tape will make them tighter. No, non-UST's are in fact looser. UST tyres have extra rubber sealing around the beading to stop the burping effect and makes the initial inflation easier by being tighter seal when deflated.

What are the lightest UST's, and what do you all use?

I tried what you did, but couldn't get them to seal easily enough without a rim strip.

Now using Stans standard rim strips and they go up nicely.

I use a non-UST Big Earl 2.5 tubeless on my 719s – had to use a bmx tube as a rim strip to get it to seal but it's been fine since then – lots of fast rocky riding in the Lakes with no burps.

It did roll around a bit at very low pressures but I think that was as much to do with using 2.5 tyres on slightly narrow rims. They were fine at around 25 PSI.

Ideally I am looking for UST's at 2.1 or below, mostly because I have a Scott carbon frame with very narrow tyre clearance! trying to keep the weight down as well.