How interchangable are 700c and 27" rimmed wheels? I've heard you need new tires, and it would depend on the clearance of the frame, but would it be noticable to run, say, a 27" on the back and a 700c on the front?

Ideally, I wouldn't want a riding poistion like this https://www.wattagetraining.com/ttSetup/images/bike.jpg as it is supposed to be a winter training bike i'm building up

Asking out of desparation really, as I can't get hold of a 700c flip-flop rear wheel on my cash-strapped budget, but found a 27"

It wouldn't be anywhere near as extreme as the photo you linked to.

Bead seat diameter of 700c rims: 622mm

Bead seat diameter of 27" rims: 630mm.

Distance the 27" wheel would raise the bike compared to 700c, assuming all other things are equal (i.e., same sidewall height on the tires): 4mm

And you are correct, the tires are not interchangeable. That's really the biggest drawback of 27" wheels these days, the tire selection isn't very good. But good 27" tires are still out there-

A 27" rim is 630mm
A 700C is 622mm
8mm is about .32"
A 27x1-1/4" (630x32) tire would supposedly have the same diameter as a 700x36C (if they made one).

The brake pads would have to be able to be adjusted 4mm in the caliper if used.

But to be clear, it's the 4mm difference in radius that would make the difference in ride height, not the 8mm diameter. Again, sidewall height of tires being equal-

Often the problem with swapping 27 for 700C is brake reach. Many sidepull calipers don't allow you to move the brake pads down far enough. You may need a long-reach caliper.

And a lot of bikes htat originally came wiht 27" wheels already have long-reach brakes that are nearly maxed out on their reach anyway. My Schwinn Le Tour and Traveler are both like this - had to stick with 27" wheels on both of them unless I updated to super-long reach brakes. But I had no reason - you can still get 27" rims, mainly in single-wall construction (although Sun makes the M13II and CR18 double-wall eyeletted rims in 27" size) and I had enough old wheels anyway.

not interchangeable in the true meaning of the word.In your case,well ,you can use a plate with a slot,the location of the holes needed to use your on caliper will be an eighth of an inch off.Too much to work yet not enough space for a clean hole,just a slot.I did it once,scavenging,years ago.I never recomend it,I say it now because you have only one to do and you're broke.Some want to use 700's on bikes that take 27"s but
that's not bright at all,as the man said just now,27' wheels are cheaply and easily had,even new.You'll hear more folkes state things too.You'd better get the correct wheel,otherwise it's butchery.

It's strictly a case-to-case thing with the brake reach issue, on my '83 Schwinn that had 27's originally I'm running 700c's with no problems. I'm using the original brakes, centerpulls with a lot of reach, no modifications necessary........But I'm wondering if the OP doesn't have a bike originally intended for 700c's and he's retrofitting a 27" on it instead of the other way around. That could cause brake reach problems in the other direction of course, but it sounds like maybe it's going to be a fixed gear, with maybe no rear brake at all-

In the end, it's the distance from the rim sidewall to the brake caliper mounting hole (on the fork for the front wheel and on the seat stay brake bridge for the rear). Every case can be different, and usually is - just as you say. There's likely a quote from Sheldon "Reach_is_Everything" Brown on this subject ;-)

OK interesting to hear about the Schwinn,a good one,that conversion comes-up sometimes.As far as the OP,I thought of a couple/few possible scenarios too,I shot from the hip in answering,I used a dis-similar make once it once.

That's rich...

There's no doubt that Sheldon would come up with something wittier than my nick, but he does, in fact, have something to say on "reach":

https://www.sheldonbrown.com/gloss_ra-e.html

-- scroll down to "reach"

Thanks for the replies guys...

As the man says, I am going from a bike currently running 700c (but knackered out old wheels), and looking for a fixed back wheel. I've already got a spare 700c front lying around, so it's a case of seeing whether the frame has enough spacing for the wheel to be able to move around in the rear dropouts (to ensure chain tension) without hitting the frame.

But from what I've gathered, I'm really not going to feel like I'm sloping forwards or any other silly old school lo-pro position, which is good!

Or use the shortcut: https://sheldonbrown.com/reach

Sheldon "Easy URLs" Brown

If it's a close clearance frame with short reach calipers, like one that can only take a 700 x 23 in the rear, then the 27 probably won't fit. If there's plenty of room btwn the wheel and brake bridge then you should be fine.

Off the back of this thread, I've gone ahead and bought the 27" wheel. Now looking around for a tyre to run on it - the conti gator skin and sport ranges look ok, but I've heard a few bad things about their handling in the wet, and their puncturability.

Has anyone had any bad experiences running these tyres? I'd be really interested in finding out what anyone else runs on their 27"-ers, I'm still looking around for non-amber sidewalled tyres!

In my opinion, the Continental Ultra Gatorskins are the best road tire out there in 27". The only downside is they are pricey, usually about $35 per tire. They're even very good on wet pavement. Good puncture protection, too-