You do realise that 27.5" is not a real size, the actual size is what has been referred to as 650B for decades, and they can be as small as 650mm in diameter which is actually less then 26".... 29" is simply a marketing name for a wide 700C tire. It get confusing when you look at tires outside the normal use. For example I have a mountain bike that is used as a foul weather road oriented bike, if it had 29" wheels instead of the 26" wheels it has, then there is no such thing as a 29x1.5 or 29x1.75, those tires are actually 700x38 or 700x42 respectively. If we refer to them by their ISO (or ETRTO designation) then they would be 38-622 or 42-622 which means that technically you could install a tire as narrow as 23-622 or as wide as 60-622. The other issue is, that a 27" tire can actually be smaller then a 700C tire..... A wide 700C tire can be as large as 706mm and 27" can be as small as 680mm. 27" itself is 685.8mm......

I switched my Raleigh from 27" to 700C, because I like having more tire options, and it's not just the expensive tires either. 27" is a dying size, every year there are fewer bikes that originally came with 27" wheels, rust and crashes, will continue to dwindle the supply. Conversions will also dwindle the supply, and that will make it harder to justify continuing to make replacement rims and tires in that size. If you want a new 27" wheel, even today, you need to get it custom built, and that is expensive, there are few decent tires made in that size, and for some dealers they are special order. I expect in the next 20-30 years you will need to take advantage of the NOS parts to keep that size, and they will not be cheap.

You can "feel" the difference in "smooth" where the BSD circumference is 1.29% greater? Have you considered working for the space program?

I've switched several bikes over from 27" to 700c rims, but haven't done any controlled experiments where I used an otherwise-identical rim, hub, spoke and tire, but my engineering-brain has a hard time believing this statement. All of the 27" rims I've come across have been the single-walled, non-eyeletted variety which thus can't handle the higher spoke tension. In all cases, I've switched to double-walled rims, and only one did not have eyelets.

On only one occasion did I make the switch partially for the issue about tire availability: I was moving to Europe and would have to order 27" tires from overseas, and wanted to switch my 37 year old touring bike to a modern cassette hub and dynamo hub.

Yes, the Armadillos are well made, tough and flat-resistant.

Slightly narrower than the 27" Gatorskins I've used, but more resistant to cuts from any angle and of course with a stiffer casing.

So many more choices with 700c, such that I can find more of the exact style of tire I want and usually at a better price, basic tires excepted.

I actually do about half of my riding on 700c discards, usually un-worn front tires or new-looking rear tires with a small, boot-able hole in the tread region. At the pressures I run (I weigh 145), such booted tires are still entirely reliable.

cavet: your brakes will probably fit- the old single piviot sidepulls- but if you want to upgrade to dual piviot- go long reach Tetkro's finding out the expensive and hard way myself.

Well, the 622 mm bead/700 size predated the 27" Dunlop size by at least 4 decades. The industry re-embraced 700c clinchers as the standard for road bikes.

I read just today that Dunlop introduced the 27x1-1/4" tire/rim size in 1935, and it was an entirely new set of dimensions not based on any other of the numerical "A, B, C, etc" versions of metric or other existing standards.

It was also stated that the 700c/622 bead seat diameter did precede this 27" standard, using fat tires of 1-5/8" and 1-3/4" to yield rolling diameters in the 28" range.
Likely this is how "700c" racing tubulars came to be referred to by tire maker Continental as 28", not that these thin tires measure anywhere close to that rolling diameter.

The 622 bead was a Canadian standard from around the turn of the century albeit on wooden rims. I mistakenly thought the Dunlops were early 50's. Still, I was wondering when the tubular racing wheel took over the peleton.

I hope they don't stop making 630s anytime soon, most of my bikes still roll on 27s. Tire selection is somewhat utilitarian but not too many people still racing these bikes anyway. On my 630 wheeled bikes, I use Panaracers, Continental and Vittoria and they seem to fit my needs.

Hi Wogster and all; Yes I know all the actual rim numbers well. The post I replied to didn't need an exhaustive explanation; just the descriptive terms generically applied to wheel/tire sizes. I wish the industry would use actual rim measurements too, but they generally don't. There are, and will be countless "27"" rims for many years to come. Longer than I'll care. I only use double wall (Araya) rims in this size. Very well manufactured and roll "true". BTW, there are newly manufactured "27"" rims available on Amazon. Millions of bikes with this rim are still in service all over the planet. However, if the Martians arrive and vaporize all "27's", new, used and otherwise, then I'll adjust to something else, no big deal.
Also, for DiegoFrogs comments; Yes, You, I and anyone else can tell the difference in "rough surface" rolling characteristics of the"27"" vs. the "700". It's not only a rim radius/diameter ratio, but spoke length, hub flange radius vs. rim radius and can include dish variation based on the cluster/free wheel width, tire inflated profile, etc. Numbers can tell a story, we just have to include them all. You may remember the move to larger flange diameters, and then down again. Stiffer ride with little or no appreciable gain in performance and other things.
Also the remark about working for the space program: I did manage an aerospace R&D metallurgical lab for my humble career, but that work was absolutely no help for sensing cycling vibration or lots of other things.

I'm with DiegoFrogs on the controlled experiments question. 1.29% is a lot to ask from measurement capability in such a subtle and complex parameter as "smoothness", and not very easy to meet in a system with so many confounding and/or uncontrolled variables, e.g.: tire pressure, individual rim variations, individual tire variations, spoke tension, spoke length; to name the ones that first come to mind.
Speaking for myself, I wouldn't bother going after or worrying about a 1.29% difference in "smoothness" between 27" and 700C wheels. Now, if there is a difference greater than that being perceived or measured, it must be due to something in addition to or besides the difference in rim diameter.

I have an old Swedish Maraton bike that I love but now I can't find replacement tires and tubes "27 1x1/2 ISO 609" for it. Does anyone have any advice about (1) where to find them ... perhaps in Sweden or Denmark? or (2) what size tire might be a workable substitution? Thanks, I don't know much about these things.

STOP IT!!! This is a zombie thread. If you care about this topic, search for a newer, more relevant thread.

The post is from a newbie.