Cycling UK Forum

ive a frame with canti brakes with 27 in wheels will 700 c work with the brakes
thanks

Please add a side-on photo showing how much the blocks can be moved.

Jonathan

That can't be easily answered without clear photos of your brakes and how much room for pad height adjustment there is available.

Probably . I have 3 Trikes that have front cantilevers intended for 27" wheels and run all on 700's quite successfully .
As previous need to see clearances and also what brakes you have . Some are more flexible than others.
Mine are Mafac / Weinman / Dia Compe cantis .

700C wheels are 4mm. less in radius than 27".
If your blocks can be moved down by this much, and still hit the rim squarely, you have a good chance of being able to make the substitution.
ETRTO diameter 622 as against 630.

only if you can somehow cope with the 4mm smaller 700C rim radius. Many cantis include provision for some block adjustment, but it isn't always obvious. BITD I brazed bosses on to a number of frames, and in every case they could use either wheel size, because despite appearances, the BR-AT50 brakes had ~4mm of vertical block movement available.

Brucey wrote: ↑14 Jun 2024, 7:55pm only if you can somehow cope with the 4mm smaller 700C rim radius. Many cantis include provision for some block adjustment, but it isn't always obvious. BITD I brazed bosses on to a number of frames, and in every case they could use either wheel size, because despite appearances, the BR-AT50 brakes had ~4mm of vertical block movement available.

I once had a tourer made for 27 inch wheels, which I converted to 700c for ease of tyre choice, and my existing cantis coped with the lower wheel rim. It was a long time ago so I don't remember the details, and maybe I was just lucky, but I had working brakes. Close-up photos of the brakes and rims from various angles would help.

It may also be possible to file the fork drop out to give you a few more mm's.

A picture is worth 50 posts.

with older designs (eg Mafac) which use post mount brake blocks, mounted where the radius of movement around the boss cannot be varied, it happens that the ideal position for the post mountings (so the brake block contacts the rim squarely) is about the same for some older 27" rims (eg. birmalux) as it is for parallel-sided 700C designs. This occurs because the braking surfaces on the larger 27" rim are angled. This means that, sometimes, conversion can be easier than anticipated.

The width of the rim has some bearing on whether it works too.
If the frame was designed for wide 27” wheels and you fit narrower 700c the brakes might meet the rim at the right height but the arc of closure might be extreme and result in rapid block wear and frequent adjustment.

There should be enough adjustment in the cantis to facilitate it.

If older brakes like Mafac, you won't have the same level of adjustment

peetee wrote: ↑15 Jun 2024, 8:20pm The width of the rim has some bearing on whether it works too.
If the frame was designed for wide 27” wheels and you fit narrower 700c the brakes might meet the rim at the right height but the arc of closure might be extreme and result in rapid block wear and frequent adjustment.

I guess I was supposing that any bike old enough to have 27"wheels would also have the bosses close together, but maybe I was wrong.

Brucey wrote: ↑17 Jun 2024, 7:09pm

peetee wrote: ↑15 Jun 2024, 8:20pm The width of the rim has some bearing on whether it works too.
If the frame was designed for wide 27” wheels and you fit narrower 700c the brakes might meet the rim at the right height but the arc of closure might be extreme and result in rapid block wear and frequent adjustment.

I guess I was supposing that any bike old enough to have 27"wheels would also have the bosses close together, but maybe I was wrong.

Of the two of us, I’d say the likely wrongness is mine.
By a long way.
Nevertheless, I thought it was worth mentioning, if only to look clever.
For a little while.