I was wondering if I would have to use a 28" frame if I wanted to use a 26" wheel with a 3" tire.
Re: Yuni frame with 3" tire
no a 26" frame would do but it would be to naroow and using a 28" wouldnt fix the narrowness you would need a wider frame
well unicycle.com sells yuni framed cycles with 3" tires so I don’t think it’s to narrow. The reason I asked was because on the 24" cycle they sell says they used a 26" frame for clearance of the tire. So it just made me think.
it would need to be a frame made for a 26x3 wheel, which if I’m not mistaken will actually fit a normal width 28 inch wheel. but a normal 26" frame obviously won’t fit a 26x3 wheel, and a normal 28" frame won’t fit a 26x3 wheel.
I think that’s right, I could be wrong somewhere…
Aren’t all the Yuni frames the same?
well I just looked again at the frames online and here is what it says “The 20-inch easily fits a Monty 20 x 2.5-inch tire; the 24/26/28-inch accepts the fat 3.0-inch downhill knobby tires. If you’re planning to use the Nokian Gazzaloddi 24 x 3.0 tire, order the Yuni 26-inch frame.” so maybe it’s only for the 24 x 3.0 tire that you need the bigger frame but I’m still not sure.
just email UDC and ask them
I have two different 26x3.0 gazz tires, one on a 2003 Yuni 26 and one on a 2005 Yuni 28; they both fit, though the 26" frame has very little clearance.
Thanks tholub 
I use Nimbus frames which I believe are the UK equivalent of yuni.
Each frame size comes in two froms- rounded top and flat (square) top, and this is a factor when it comes to fitting in tires.
For example, my 28" round frame would take a 29-er tyre- but only just; whereas a square top 28" fits it really well with plenty of clearance- it also accepts the 29"‘big apple’ tyre, which the round top one doesn’t.
My advice is to get the 29-er frame; I’ve got this and it takes all 29" tyres and also my 26 x 3 Gazzalodi.
I have put a Gazz 24x3 on a 24" yuni frame, it fits but there is not a lot of room for mud clearance.
I had a 26x3 gazz on my 26" yuni frame, and it fit, but the clearance was really tight. Also, one leg of my frame was slightly longer than the other, so to stop the tire from scraping the side I had to put in a shim to even out the length. It does work though.
I am running an Arrow Racing 24x3.0 Prime Wide in my Yuni 24" frame and there’s no problem with clearance… I believe the Gazz is a special case of a 24x3.0 tire.