I have a Schwinn unicycle that I purchased new in 1994 from someone’s secret stash. If it helps to identify the cycle, here are some of the features:
Non-cottered crank
White pedals
Blue decal with white SCHWINN lettering on the forks
Blue “Viscount” seat with white plastic bumpers.
Blue rim marked “SUN METAL PROD. INC. 05-91” with 1-inch inside width.
National Tire Co. Panaracer Unicycle H-P, 24x1.75, blue tire with white sidewall
The original tire has gotten hard & crumbly. I can’t use that. I bought a replacement 24x1.75 tire made by Hwa Fong, with the brick tread pattern and white sidewall. I may have had trouble with it staying seated at the rated 50psi pressure – that was several years ago. Then I got the idea that I wanted a semi-slick high pressure road tire and somehow managed to track down an IRC Metro 24x2.0. However, it definitely does not stay seated at its rated maximum pressure of 85psi. At one point I went through several tubes trying to determine the real maximum safe pressure, but I don’t remember what it was. Now I want to ride again, and I’m trying to figure out why I am having so much trouble.
The IRC Metro is marked “to fit 24x1.50-1.75” rim. I measured my rim, and it is 1" on the inside. Is that my problem? Are there any high pressure slick tires for a 24x1.00" rim?
I just put the Hwa Fong “brick” tire back on and pumped it to 50psi and took it around the block. It seems to work just fine. Now I remember that the seating problems were with the original tire, which had picked up a kink in the metal bead at some point.
The blowouts I have gotten with the IRC Metro are probably due to too wide a tire (2.00") for my 1.0" rim. If you’re in the SF Bay Area and would like to buy a nearly un-used IRC Metro 24x2.00 tire really cheap, drop me a note.
> The IRC Metro is marked “to fit 24x1.50-1.75” rim. I measured my rim,
> and it is 1" on the inside. Is that my problem? Are there any high
> pressure slick tires for a 24x1.00" rim?
>
Not all 24" rims are alike. One problem is with older tire sizing the
diameter number wasn’t the rim diameter or bead seat diameter, I think
it it was outside tire diameter of some nominal tire. It doesn’t make
much sense now, but that’s how they did it back then.
The tire on my Schwinn says “24x1 3/4 to fit S7” rim. This doesn’t
quite match the chart in the link below which says S7 is a 26" size.
Nor is that size found on the chart. But that link might be interesting
anyway.
In tire sizing a 24 x 1-3/4" tire is not the same as a 24 x 1.75" tire. They are two different sizes to fit two different size (diameter) rims. It makes no sense, but that’s the way tire sizing happened.
Schwinn used the odd-ball 1-3/4" size which fit an odd-ball S7 size rim. It’s not a true 24" rim in the way we think of standard 24" rims. So you need a special tire for it. The tire needs to use fractional sizes rather than decimal sizes. Your bike shop will be able to order such a tire. Tire choice, however, is going to be very limited.
Schwinn did the same with their 20" unicycles using a similar odd-ball size tire. It didn’t fit the standard 20" tires that BMX bikes use.
One option is to rebuild the wheel with a standard 24" rim so you’ll be able to use regular 24" tires. The problem there is that a wheel rebuild with a new rim and new spokes and wheel build labor will be spendy (figure $70 - $80 or so give or take $20). The advantage there is that you’ll get to use standard tires from now on and you’ll get to select a good strong rim that is better than the stock rim. That was the option I went with when I upgraded the wheel on my Schwinn giraffe. The giraffe now uses a standard 20" tire.
David’s link to Sheldon Brown describes the oddities in tire sizing.
I’m aware of the distinction between 1-3/4" and 1.75" widths. As you can see, I listed the original tire as a 24x1.75, which is exactly how it’s marked. I don’t have one of the older cycles which use 24x1-3/4" tires.
I’ve measured the bead seat diameter, and 507mm is the closest size on Sheldon Brown’s chart. The “traditional designation” for that ISO diameter is 24x1.50 - 24x2.125.
I honestly think that the problem is that I have a 1.00" wide rim and the tire is designed for a rim that’s 1.50" to 1.75" wide.
> I honestly think that the problem is that I have a 1.00" wide rim and
> the tire is designed for a rim that’s 1.50" to 1.75" wide.
Since the rim is 507mm, and there doesn’t seem to be a slightly smaller
rim size, I guess it points to that. Surprising if true though–on MTBs
it’s common to run wider than 2.0 tires with narrower than 1" wide
rims. They’re made to be compatible though.
I thought the “fits 24x1.50-1.75” on the tire was all about replacing
those tire sizes and not at all about rim width, but maybe I’m wrong.
Welcome Orthonormal! There is a large community of Bay area riders, who have a mailing list for rides they do, sometimes more than one a weekend. This weekend is the California Mountian Unicycle Weekend at Lake Tahoe, and next weekend (Setp. 29-Oct. 1) is the Berkeley Juggling/Unicycling Festival.
Your Schwinn is from the “modern” era, the most advanced unicycles Schwinn made. They were made from 1986-93. Then there were none for two years, and in '95 they came out with a “retro” version that lost some of the improvements they’d made in the 80s.
All of those Schwinns (everything from 1986 onward) use 1.75 rims, not the older 1 3/4 dinosaurs. Sounds like your IRC Metro tire was just too wide. Here are some 24" tire choices at Unicycle.com: http://tinyurl.com/5cta9
The last one should definitely fit your rim.
Or maybe not perfectly, as the rim you described may not be the original rim. I thought those blue Schwinns used Araya rims? But maybe not…
I am pretty sure that it’s the original rim, since the unicycle arrived brand new in a Schwinn box with that rim. I do have the last tire on that list (the 24" Schwinn white wall tire), it’s the 2nd tire I described, and what’s on the uni now.
Unfortunately, I think the one I have is defective. There is one spot on the bead that always rides up. Now I remember why I went looking for a new tire. Maybe I will just order another one of the same model.
David, that’s what I originally thought, but it actually says “to fit 24x1.50-1.75” rim". If it were meant to be a replacement for a 24x1.75" tire, then I can imagine repeating the process with a 24x2.25" tire that’s meant to be a replacement for a 24x2.00" tire, and so on. I am a little bit surprised that it doesn’t work anyway, since such a wide range of tire sizes fit on my MTB wheels.
Update: I contacted tech support at Schwalbe tires because they had a few tires that looked like they might fit. I described my problem, and got a helpful and detailed response back from Tim Unger. Tim suggested that older rims with the folded over lip don’t grip the tire’s bead as well as modern extruded rims. That, and maybe the tire really was too wide for the rim.
So what the heck, I’ve ordered a 24x1.75" (507mm) rim and some spokes, and I am going to attempt to build the wheel myself. The IRC Metro tire should fit perfectly, and the path is open for even fatter tires if I ever wear this one out.