Can the old 27" tires be used on 700c rims?

Nope

I kinda figured that, my conversion calculator came up with 27.58897.
Thanks for the conformation

Don't try to calculate wheel & tire sizes. Many times, the numbers have very little to do with the actual measured "size". It's far better to consult the shade of Sheldon: https://sheldonbrown.com/tire-sizing.html

I'm a mountain biker, the whole road bike tire thing is a mystery to me, is 700 and 700c 2 different things?

MTBerJim, There are two types of 700 tires available for road bikes, tubular (sew-up) and clincher (seperate tube) and the C stands for clincher.

Brad

In general, no.

99.99% of the time, 700 means 700C (note that it's a capital "C"). For a couple years, GT offered a "700D" tire, which is now nonexistent: https://www.sheldonbrown.com/harris/tires/587.html

Read the Sheldon Brown page. Even though he's been gone for several years, the information is still quite relevant.

You're a mountain biker? Don't even get me started on the 6 different sizes of "twenty-six inch" bike tires.

Wrong. Read the Sheldon page (please!). Long ago there were 700A, 700B, and 700C tires. They were all the same outside diameter, but since the "B" and "C" tires were fatter than the "A" tires, the corresponding rims were smaller. Eventually, "700C" rims were the de-facto standard for "racing" bikes, and tire width changed while the rim diameter stayed constant.

I skimmed the page just now, 700 and 27" not the same. It's a good read, I'll get more in to it tonight.
Mountain bike tires are easy, 26" no matter what, Kevlar or wire bead-tubes or no tubes, from 1" to 3" wide. what's so hard to get?

Yes, but 29" mountain-bike rims are the same diameter as 700C- figure that out. And the Surly Endomorph tires go all the way to 3.7" wide- way phat.

26" mountain bike rims are fairly standard, but they're not the same as 26" road bike tires (aka 650C) or 26 x 1 3/8" (which are further divided into Schwinn and non-Schwinn sizes) or 650B (sometimes called 26 x 1 1/2"). Trust me- bike tire sizing will make you crazy.

It would be much less confusing if the actual measurement were specified. There are at least 5 different rim sizes that are all called 26":
559mm (the mountain bike size), 571mm, 584mm, 597mm, and 599mm. I first encountered the problem almost 50 years ago when trying to buy a replacement tire for my Schwinn 3-speed. The tires on it were labeled 26 x 1 3/4" so I went to a store that sold bike tires and they had some labeled 26 x 1.75". Knowing that 1 3/4 = 1.75 I figured that should fit and brought one home. Spent the next couple hours trying to get the tire on the rim, but neither I nor my father had any luck so we finally went back to the store. There we learned that the Schwinn 26" rims were just a little bigger than the 26" rims used by most other bike makers at the time and that we'd have to go to the Schwinn dealer for tires that fit.

Similar situation with 27" and 700c - no way to tell from the names what the actual sizes are or by how much they differ. If we switched to using the actual measurement we'd refer to 27" rims as 630mm and 700c ones as 622mm which would make the situation much clearer. On top of that, the 622mm size is sometimes called 28" and in the MTB world is called 29" despite being a slightly smaller rim than those called 27".

Don't get ME started on the 29" mountain bikes, you wouldn't like my Retro Grinch

That's why I like the ISO/ETRTO tire sizing- thankfully becoming more prevalent.

MTBerJim- see what you started?

Sorry about this Jeff, although I'm getting the impression your a glutton for the punishment.

Darn right. Just ask my wife:

This is exactly what prathmann was saying above, but it's a pet peeve of mine so here I go.... I think what makes this so confusing is that the stated size (26", 29", 700c, 27") are the estimated diameter including the tire, but people use the numbers for "rim size". It is not the rim size. So even though the 700c and 29" use the same rim diameter (622mm ~ 24.5"), the 29'er generally uses a larger tire and therefore has a total size that is larger than the 700c (700 mm ~ 27.5").

And of course, ultimately the actual total diameter depends on the size of the tire itself.

This is just stupid and I can't for the life of me understand why companies and people don't just use the actual rim diameter. Of course this info is printed on every tire and tube you can buy, so why don't we use it.

There are Standards.. the ISO/ETRTO, to keep rim
and tire manufacturers on the same page.
they agree on tire bead seat diameter.. and print that on tires,
27'' = 630mm '700c = 622mm ..

tire width is a second number .. like 622-32 ..

Jeff, Thanks for the correction, I've been incorrect for decades! Evidently 700C has taken on the wrong meaning in common language as even wikipedia is incorrect:

700C Road bicycle wheels / ISO 622
Touring, race, and cyclo-cross bicycles may have vastly different design goals for their wheels. The lightest possible weight and optimum aerodynamic performance are beneficial for road bicycles, while for cyclo-cross strength gains importance, and for touring bicycles strength becomes even more important. However this diameter of rim, identical in diameter to the "29er" rim, is by far the most common on these styles of bicycles. It rolls more easily than smaller diameter tires. Road wheels may be designed for tubular or clincher tires, commonly referred to as "700C" tires.

An interesting link:

https://en.wikipedia.org/wiki/ISO_5775


Brad

Nope. 700A is an obsolete rim that measured 642mm at the bead. 700B is a mostly obsolete wheel size that measures 635mm. 700C is a rim that measures 622mm. 700D is a 587mm rim size that GT tried to make popular...and failed miserably. In the original French system the letter designation referred to the tire width. An 'A' was narrow and a 'C' was wide but that system was soon abandoned. Clinchers and tubular tires don't have a designation that I know of. Both use 622mm rims.

A 29" mountain bike wheel is really just a rebadged 700C rim. Same size: 622mm

I've also seen bikes at department stores with ISO 622mm rims labeled 28 inch. Go figure. Presumably they want to make it sound similar to all the other tire sizes (20", 24", 26", etc.)

I too wish all the dumb names be done away with and just use the ISO/ETRTO system.

It comes from the silly method that is used to size the tires. The 'size' is based on the outside diameter of the tire when mounted on the wheel, not on the diameter of the rim. A 27" tire that is about 1" wide (and high) will add 2" to the 24.8" of a 630mm '27"' rim. It's close to 27" outside diameter. If the tire is 1.5" that's very close to 28". A 29er using 2.2" tires adds enough to make them - almost - 29" tall. It's a dumb system but then it's only one thing among many goofy bike things.

there is a 700 A , and B, also. A: 642, B:635. so bigger rim than 27"

and a 650 A,B,C. more common, 700C & 650B.
Ref : Sutherlands