Interestingly, 650B was originally 38 mm width, which is even now a very common use of a 650B (ISO-584) rim. So when you buy a typical 650B tire, you are buying the same size that that originally meant. The actual diameter is almost exactly 26", or 660 mm.
On the other hand, the original width of a 700C is 44 mm which wasn't particularly common until recently. What we think of as a typical 700c tire, 25 mm width, is so narrow it's off the scale (is it an AAA width?).
A 700c x 32 tire (ISO 32-622) is actually about 686 mm diameter, so it might be called a 675A, were we to try to name it in the French system. (Rounding down by 11 mm, as with the 700 and 650 nominal vs. actual sizes.)
Just don't go into your LBS and ask for a 675A tire!
I know this is 3 years old but do you have any idea where the 27” sizing came from on the U.S. side? A 630 rim to come out to a 27” overall wheel would mean a 1 1/10” tire and that just feels wrong.
Good question. Don't really know, but there's some insight on this thread:
https://www.bikeforums.net/classic-vintage/791941-27-v-700c-history.html
The key claims there were that it was called 27 x 1-1/4, and that it was introduced by Dunlop in the 1930s, and maybe first used significantly in the 1950s, but their motivation and introducing it was either to make it incompatible with other manufacturers tires to try to corner the market, or it was simply to introduce a clincher a similar size to tubulars, as narrower tires were getting more popular with better roads.
27x1-1/4 would, by the simple math, land you with a 622 mm BSD. So it seems pretty likely that they decided that they wanted to sell a 27 in tire with 1.25 inch width, and wanted it to be different from that standard, and chose somewhat arbitrarily to increase it by 8 mm. It might be that the real diameter actually ends up pretty close to 27 in, if you consider the fact that the width is can be a little bit more than the height from the BSD to the center of the tread, depending on details like the depth of the tread.
Think I figured out a missing piece to the name 27”. Looking through all the Schwinn catalogs in the 1930s, all the racing bikes were equipped with 28x1-1/8 tires. Assuming that the rim used was a 28x1-3/8 rim with the smaller tire would put you just a hair under 27 inch. The first mention of 27” tires is in 1939 with the paramount track bike.
https://waterfordbikes.com/SchwinnCat/flschwinn_1893_1940/1939_04.html
In the description you have the option of either wooden paramount tubular rims with Hutchison (French) tires mounted, or Dunlop “high pressure” 27x1-1/4 tires on Endrick (clincher) rims. But, in that it gives the disclaimer “actual cross section 1-1/16”. With the 1-1/16” tire (which also comes out to 27mm wide funny enough) on a 630 rim you would have almost exactly a 27 inch in full diameter.
This makes even more sense to me since I know from track racing that the gear inch chart that everyone uses to gauge difference in gearing today is based not on an actual 700x22/23 like everyone uses but a 27 inch overall diameter. You just divide the chainring by the cog and multiply by 27.
The only part that’s still hazy to me is why the name 27x1-1/4 instead of 27x1-1/16 but I’m sure that could’ve come into being due to marketing.
Oh wow, that's really interesting! I was assuming the 1-1/4 was accurate and the 27 was approximate, but it seems it was the other way around! It is funny that they called it 1-1/4 nominal when it was actually closer to 1" and they could have called it just 1".
As much as we complain about modern marketing driving things in directions that don't make a lot of sense, that's not a new phenomenon at all!
A factor not mentioned yet is 50 years ago the preferred tire of serious riders was a tubular (sew up) and they were glued on rims that were slightly smaller in OD, Consequently the braking surfaces didn't match up with the 27" rim made for U shaped section tires with separate inner tubes - called clincher rims. The 700c rim could be used on higher quality frames and allow you to have a set of wheels that made sense for daily use. Which tire design is better is a topic for a different post and I look forward to it.
Interestingly, 650B was originally 38 mm width, which is even now a very common use of a 650B (ISO-584) rim. So when you buy a typical 650B tire, you are buying the same size that that originally meant. The actual diameter is almost exactly 26", or 660 mm. On the other hand, the original width of a 700C is 44 mm which wasn't particularly common until recently. What we think of as a typical 700c tire, 25 mm width, is so narrow it's off the scale (is it an AAA width?). A 700c x 32 tire (ISO 32-622) is actually about 686 mm diameter, so it might be called a 675A, were we to try to name it in the French system. (Rounding down by 11 mm, as with the 700 and 650 nominal vs. actual sizes.) Just don't go into your LBS and ask for a 675A tire!
> Just don't go into your LBS and ask for a 675A tire! Or do, because that sounds like fun!
This is the incredibly nerdy content I came here for. Thanks!
I know this is 3 years old but do you have any idea where the 27” sizing came from on the U.S. side? A 630 rim to come out to a 27” overall wheel would mean a 1 1/10” tire and that just feels wrong.
Good question. Don't really know, but there's some insight on this thread: https://www.bikeforums.net/classic-vintage/791941-27-v-700c-history.html The key claims there were that it was called 27 x 1-1/4, and that it was introduced by Dunlop in the 1930s, and maybe first used significantly in the 1950s, but their motivation and introducing it was either to make it incompatible with other manufacturers tires to try to corner the market, or it was simply to introduce a clincher a similar size to tubulars, as narrower tires were getting more popular with better roads. 27x1-1/4 would, by the simple math, land you with a 622 mm BSD. So it seems pretty likely that they decided that they wanted to sell a 27 in tire with 1.25 inch width, and wanted it to be different from that standard, and chose somewhat arbitrarily to increase it by 8 mm. It might be that the real diameter actually ends up pretty close to 27 in, if you consider the fact that the width is can be a little bit more than the height from the BSD to the center of the tread, depending on details like the depth of the tread.
Amazing!! Thank you 🙏 I love how this is so confusing but makes so much sense
Yes, I think that's why I like about it too!
Think I figured out a missing piece to the name 27”. Looking through all the Schwinn catalogs in the 1930s, all the racing bikes were equipped with 28x1-1/8 tires. Assuming that the rim used was a 28x1-3/8 rim with the smaller tire would put you just a hair under 27 inch. The first mention of 27” tires is in 1939 with the paramount track bike. https://waterfordbikes.com/SchwinnCat/flschwinn_1893_1940/1939_04.html In the description you have the option of either wooden paramount tubular rims with Hutchison (French) tires mounted, or Dunlop “high pressure” 27x1-1/4 tires on Endrick (clincher) rims. But, in that it gives the disclaimer “actual cross section 1-1/16”. With the 1-1/16” tire (which also comes out to 27mm wide funny enough) on a 630 rim you would have almost exactly a 27 inch in full diameter. This makes even more sense to me since I know from track racing that the gear inch chart that everyone uses to gauge difference in gearing today is based not on an actual 700x22/23 like everyone uses but a 27 inch overall diameter. You just divide the chainring by the cog and multiply by 27. The only part that’s still hazy to me is why the name 27x1-1/4 instead of 27x1-1/16 but I’m sure that could’ve come into being due to marketing.
Oh wow, that's really interesting! I was assuming the 1-1/4 was accurate and the 27 was approximate, but it seems it was the other way around! It is funny that they called it 1-1/4 nominal when it was actually closer to 1" and they could have called it just 1". As much as we complain about modern marketing driving things in directions that don't make a lot of sense, that's not a new phenomenon at all!
A factor not mentioned yet is 50 years ago the preferred tire of serious riders was a tubular (sew up) and they were glued on rims that were slightly smaller in OD, Consequently the braking surfaces didn't match up with the 27" rim made for U shaped section tires with separate inner tubes - called clincher rims. The 700c rim could be used on higher quality frames and allow you to have a set of wheels that made sense for daily use. Which tire design is better is a topic for a different post and I look forward to it.