Went to go for a ride this morning, and my front tire is dead flat. I had been expecting this eventuality, and was prepared, or so I thought. I found a tube on the shelf and as I'm opening the box, I see the words "3-speed only." Huh.
Now, my bike happens to be an old mountain bike frame, and I've been running road slicks on it for decades, but it isn't a 3-speed. How can it matter? Rims are 26". Tires are 26" x 1.25". Tube is 26" x 1.25". We're good, right?
Well, maybe. As I'm putting the tube in the tire, I see perhaps a bit more "extra" than usual. In the end, I have to stuff the extra tube into the tire as I'm slipping the tire onto the wheel. Of course, I used some cornstarch baby powder. Tube seemed bunched up in a couple places. I'll put air in it and see what happens.
I aired it up to 60 psi (tires are good for 100) and went for a ride. Seems fine. Is it?
So is there something different about a "3-speed" 26 x 1.25 tube and any other 26 x 1.25 tube?
Probably no different.
I have used 26 inch tubes in a 29 inch wheel and vice versa when in a pinch.
It doesn't seem to make much of a difference.
In reply to wvumtnbkr :
Yeah, prolly right. I've heard of the excess rubber getting pinched and causing problems. Tube just didn't fit as well as most I've used.
I've worked on some of those old 3 speeds and haven't come across this, but I had to look.
So it's real. That's a fractional tire as used on a lot of English 3 speeds. It's for a wheel that's 590mm in diameter. A 26" mountain bike wheel is decimal and the rim measures 559mm. That's quite a difference! It has to do with old tires being measured by tire diameter instead of wheel diameter, it seems.
As always, Sheldon Brown knows all.
What Keith said.
It's totally a thing.
Most common 3-speed size is 26x1 3/8. I think one of the conventional giveaways is fractions vs decimals, but that bead diameter Keith pointed out is the definitive item (and is usually somewhere on the sidewall).
Er, but Sheldon Brown is much better than my recollections from working at a bike shop twenty years ago...
I've spent the last 25 years working in the bicycle industry, and the biggest lesson learned here is that fractional sizes aren't equivalent to decimal sizes. A 26"x1.25" is not a 26"x1.25" tube when the box is marked 26"x1-1/4"
When in doubt, look for the ISO (should be on the sidewall of the tires, and possibly also in the rim, in a XX-XXX format, where the first two digits are the width in millimeters, and the last three are the diameter of the bead seat in millimeters) rather than the nominal size...or check with Sheldon Brown!
26 inch sizes are a dangerous minefield because not only are there 26" decimal MTB/beach cruiser tires (559 ISO) and 26" fractional 3-speed/British tires (590 ISO) but berkeleying Schwinn went a created their own 26" fractional size which they used on 3-speeds (597 ISO)!!!
20" tires can be a 406 ISO (decimal size BMX bike) or a 451 ISO (fractional size used on some recumbents and oddball youth bikes.) 24" can mean one of four different ISO 507, 520, 540, 547....and so on.
The current bike industry clusterberkeley of standards has roots in each nation having different early 20th-century standards, and then the late-20th-century more-global industry standards that emerged being a weird mish-mash of mostly British, American, and French standards.
ShawnG
UltimaDork
9/5/21 12:10 a.m.
And for some perverse reason, the bottom bracket is STILL English thread.
Thank you, gentlemen! Learn something new every day. The rim is 559 x 21. Tire says 32-559. And that tube is obviously larger.
As it happens, I found a correct tube that I had hidden away in my trunk bag on the actual bike! Naturally, I found it AFTER I had installed the too big one and re-installed the wheel. This tire was "new" but in fact had a few miles on it where I lost the tube and rode on it more or less dead flat for a couple miles to get home. I'm not sure it's in a condition where I'd trust it. Looks like I'll be getting a new tire and putting on the other tube. I believe it's a Continental in the correct size.
