I'm actually just curious. As far as I can tell, there is no apparent difference in ride or strength. Was it style or a desire to come into compliance on a race rule? Was it a combination of both or did a couple of bike designers just decide it was a cool wheel size?

700c (622mm) and 27" (630mm) rims were diff standards, from Europe and the U.S., I think. Higher-end American bikes mainly had 700c wheels even in the '70's, and my guess is that racing's influence pushed the U.S. toward all 700c during the 1980's. But I really don't know much of this history. It's a question for Sheldon, and probably for many others who are older than I.

Tim's right. 27" was strictly an American/British size and most of the bikes made or imported here were of middle to low quality.

By the 60's and 70's most really good quality bikes came from Europe (primarily France and Italy) and were equipped with 700c wheels so these became the mark of a "serious" bike. The Japanese followed the European model and used 700c wheels on their better bikes and it became the standard.

I think that another nail in the 27" coffin was that there were a lot of bikes with tubular wheels....the ability to swap into and out of clinchers was attractive and that worked best with 700c. There have been lots of wheel standards over the years but I never quite got why 27" got started. I wonder if it wasn't some marketing ploy to produce an answer to a question no one asked....

Good thought and I'm sure that was a factor. Again, "serious riders" used tubulars and 700c clinchers so they were copied by everyone who wanted to look serious.

I think 27" wheels were developed in England, probably before or at least contemporary with 700c. The Brits always go their own way and didn't care what the Europeans were doing. Ever see the headline reported to have been in a British newspaper: "Fog Covers Chanel. Continent Isolated."

I think 27s(clenchers) were developed to compeat with sprints(sew up) and were a 700(622) rim with a bead added which made the rim size 630.Dunlop developed the 27 and also dunlop developed the wire bead tire.
That my guess anyway???

May I suggest that 700c (622mm) was chosen because it was the largest wheel that would make a bike. On road bikes with little tiny tires, the ability to role over irregular surfaces is even more critical than on MTBs where you can pack lots of air and rubber on to keep the rim safe.

OK, thanks all! I was curious and I got SOME answers aty least, or decent opinions!
Ah well, it appears to be one of those mysteries, and I think I did see that headline in a book on Cultural Morphology discussing some of the quirks of British culture (NOT a hit at you English, just relating a scrap of text!

I'm relatively certain that 700c came awhile before 27", in my understanding of bicycle chronology. I have seen some wooden rims from the turn of the century that were 28"/700c according to their owner.

metric sizing won over english sizing... it happened in my car too..

frameteam2003 is closest to the mark. Dunlop introduced 27" to produce a guaranteed market, otherwise they'd have to compete with European manufacturers in 700C.

All of the above are correct, some additional details. 700c where mainly sew-ups while 27 where mainly clinchers. in the late 70's early 80's, when nice quality bike came from Japan, there was a revolution in tires. Good quality clinchers where being made in both sizes, by good quality I mean kevlar bead light weight tires. So you could hav a folding tire, for a spare, that you could pump up to 100+ lbs, with the convience of a clicher, ie no glue to change a tire. And the race was on, Bicycling magazine had an article, titled something like 'Which will win; 27 or 700'. Need less to say we now know who won(and which of us backed the wrong horse). The bottom fell out of the Japanese bike import industry due to increased tariffs, and with it went any support for the 27" wheel. Along with some good components not made by Shimano, my Suntour Cyclone will still stand up to campy, and that is a loss for us all. If you want to get some blank stares, and cause mass confusion, go in to your LBS and ask for 27x1 tires with a kevlar bead.

Who makes the 27"X1" Kevlar Bead? I'd love to find some myself and knowing who does make'em might help me out!

Tom I haven't seem them since the early 90's. Specialized made them, sorry for get the name. I also kind of stopped riding that bike, heavy tires, and friction shifters, aren't much fun for me any more, the index shifter revolution spoiled me. Check Performance, and Nashbar.

Oddly enough many places in Europe call 700c rims 28 inch rims. It's the *only* thing I've ever seen measured in inches in Europe. Go figure....

Some bicycle fittings are still spec'ed in "English" measurements.

English (ISO) bottom bracket cups are 1-3/8" diameter (often seen as 1.37 or 1.375 or as their metric equivalent of 34.9 mm) and 24 tpi (threads per inch). Even Italian bottom brackets used the mixed measurements of 36 mm x 24 tpi.

The new "oversize" handlebar and stem diameter is 1-1/4", again sold under their metric equivalent as 31.7 or 31.8 mm (the exact measure is 31.75 mm) and steerers are either 1" (25.4mm) or 1-1/8" (28.6 mm).

Harris Cyclery has some beauties, I'll plug Sheldon's stuff anytime because he just plain rocks. He's got interesting pages on wheel and tire sizing too, on his site. Go here to see the tires, scroll down for the narrow, folding Avocets (27 X 7/8), and also Panaracer 27 X 1:
https://sheldonbrown.com/harris/tires/630.html