I often scan the unicycle listings on Ebay, and see a few older Schwinn models (24"). What is the quality of these older Scwinns in general??
JUNK Seat is going to wear out in nothing flat. Once you learn the cranks are going to pop off the axles. Buy at least a unicycle with a seat with a handle and cotterless cranks.
Not junk, and not worth more than $50 in great condition. That said there are a few incarnations of them. I would say that if you really want a Schwinn, get one that was made after 1984 with the blue Araya rim, and sugino cotterless cranks. Those ones have a standard size wheel that fits a normal 24" tire.
I learned on a Schwinn 20". I have a Schwinn 24" that I loan out to people, and I never worry about it.
When I think junk uni’s like the old Troxel’s, Sears, old Cyclepro’s with lollipop bearing holders, things like that come to mind.
Today’s Schwinn:
No reason to buy one. While it retains the “classic” stamped frame, it still has the bolt-thru-seatpost adjustment system, with 1" increments on your seat height. If you take your unicycling seriously, that’s a joke.
1967-79:
The classic years; cottered cranks. Cool as collectors’ items, or to hang on the wall for decor, but the seats can’t take being dropped and the cottered cranks are troublesome. Also it’s hard to find the tires to fit. Okay for learning to ride on, though.
1980-83:
Cotterless, Sugino cranks, a big improvement!
1986-93:
The blue-rimmed ones jtrops mentioned (24" only). Best version of the Schwinn. Improved seat (Viscount), a little lighter, and you can fit today’s tires on it.
1995-2000?
They went retro, and returned to the chrome & black look. A step backward.
The missing years:
They didn’t produce unicycles during those gaps. I’m not sure the dates on the most recent gap. Unicycle.com is responsible for resurrecting the Schwinn from possible oblivion. The Drummonds believed that many returning riders would seek out the Schwinn as a brand they knew they could trust.
Schwinn Giraffe, 1977-83:
An awesome giraffe. It man problem is the tire compatibility thing, but it’s worth changing out the rim. A great find if you see one on eBay for less than $200 (depending on condition).
The cotterless cranks go back to 1980 (140mm). The better rims are easy to spot because they’re blue. Harder to tell on the 20" models, which still had black seats and silver rims. I think those rims were steel, but they were of the compatible type.
Yes to the old lollipop bearing types, but the Troxels, Hedstroms and other department store unicycles aren’t worthy of the label “junk”. 
Schwinn Unicycle Tires
[QUOTE=johnfoss;1488907]
Today’s Schwinn:
1967-79:
The classic years; cottered cranks. Cool as collectors’ items, or to hang on the wall for decor, but the seats can’t take being dropped and the cottered cranks are troublesome. Also it’s hard to find the tires to fit. Okay for learning to ride on, though.
Hey, The original tires are hard to find, Got this note with a recent purchase and thought to pass it on.
I managed to snag a fairly great condition 70s Schwinn for $27. Once a part does go out on it though, especially not knowing the cost, I will probably move onto a more up-to-date uni…but the Schwinn you can say is my gateway into unicycling. Right now, I’m pretty happy with it except the fact that the seat doesn’t have bumpers on it, therefore, it doesn’t like UPD’s. Also, the incremented bolt holes are strange but luckily it fits just right for me. The frame also feels pretty sturdy despite the single bolt securing 1 end and the cranks and bearing lock rings on the other end.
Whoever had mine before must have never ridden it as the seat was in like new condition with no scuffs. After I got a hold of it and actually rode the thing, it has it’s battle scars and tears beginning to form at the seam. I may just get some black gorilla tape for a quick fix and some protection.
Wow, a potentially cool resource for all you owners of old Schwinns! However the seller failed to mention if those were black tires, or the much snazzier whitewalls. Both were made.
The other concern with such old tires is condition. Depending on how they were stored, they may be cracky and dry rotted. However mine, which have lived mostly in garages all these years, seem to be in pretty good shape. I still have one or two unused 20" Schwinn whitewalls left! not for sale. 