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27” to 700c clearance

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27” to 700c clearance

Old 02-16-21, 09:25 PM
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shoota 
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27” to 700c clearance

Any chance of getting a 700c wheel on here? Doesn’t look like much downward movement available on the rear brake.

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Old 02-17-21, 02:32 AM
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yeah, i see what you mean?
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Old 02-17-21, 03:33 AM
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Is that a 27” rim there now? That would mean the canti’s pivot and design (brake pad contact) is right at the limit (by appearances) for the 27” rim (630mm diameter). The 700C rim is 622mm in diameter or 4mm shorter radius at the brake pads.

If you want to use the 700C rims, this suggests you would need to lower the pivots if possible, get offset brake pad holders if available, or find new canti brake calipers set up for a 700C reach with the current pivots you have.
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Old 02-17-21, 03:52 AM
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It looks like your pads are at their limit now. Not much chance of getting 700’s on there if those in the photo are 27”. I have a few bikes with 27” wheels and don’t mind them. Just roll with the wheels you have, with cantilever brakes it is quite a bit more involved to change the reach.
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Old 02-17-21, 04:25 AM
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Originally Posted by Kabuki12 View Post
It looks like your pads are at their limit now. Not much chance of getting 700’s on there if those in the photo are 27”. I have a few bikes with 27” wheels and don’t mind them. Just roll with the wheels you have, with cantilever brakes it is quite a bit more involved to change the reach.
There appears to be a normal bridge with a mounting hole, could just dump the cantis and use a side-pull or centre-pull; if the arms interfere with the posts use a side-pull mounted on the front of the stays.

Mount a rack to the old brake posts.

What's the situation up front?
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Old 02-17-21, 06:02 AM
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Also, older cantis that take pads with unthreaded posts will give you more wiggle room for this kind of adjustment. I've found DiaCompe 981 work well since they
(a) take old school unthreaded-post pads,
(b) have an ovalized slot to allow some pad movement up and down, and
(c) have a geometry that accommodates a "wider spread" set-up, which helps get the pads correctly aimed at the lower level.

Last edited by niliraga; 02-17-21 at 07:02 AM.
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Old 02-17-21, 08:57 AM
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Originally Posted by niliraga View Post
Also, older cantis that take pads with unthreaded posts will give you more wiggle room for this kind of adjustment. I've found DiaCompe 981 work well since they
(a) take old school unthreaded-post pads,
(b) have an ovalized slot to allow some pad movement up and down, and
(c) have a geometry that accommodates a "wider spread" set-up, which helps get the pads correctly aimed at the lower level.
I have 981s on my Voyageur so I'm well familiar with how awesome they are. But even with those brakes I'm not sure there's enough downward adjustment available.

Originally Posted by oneclick View Post
There appears to be a normal bridge with a mounting hole, could just dump the cantis and use a side-pull or centre-pull; if the arms interfere with the posts use a side-pull mounted on the front of the stays.
Mount a rack to the old brake posts.
What's the situation up front?
Interesting, I hadn't thought of that.
The front is normal, which is why the rear setup baffled me. I mean it sure looks like a 27" wheel to me.

Originally Posted by mech986 View Post
Is that a 27” rim there now? That would mean the canti’s pivot and design (brake pad contact) is right at the limit (by appearances) for the 27” rim (630mm diameter). The 700C rim is 622mm in diameter or 4mm shorter radius at the brake pads.
If you want to use the 700C rims, this suggests you would need to lower the pivots if possible, get offset brake pad holders if available, or find new canti brake calipers set up for a 700C reach with the current pivots you have.
It's for sale locally but I haven't looked at it yet. Pretty sure those are 27" wheels. I've asked the seller for more pictures. But if those rear brake pads can't be adjusted down to fit 700c wheels I'm out, I have zero use for 27" wheels.
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Old 02-17-21, 12:28 PM
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Are there any washers behind those brake shoes? If so get rid of the washers, that will allow the cantilevers to come in more. The way canti brakes are - the more they come in the more they angle downwards.
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Old 02-17-21, 12:33 PM
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Never used them, can't vouch for them but maybe someone has.

https://www.amazon.com/BOX-COMPONENT...66484527&psc=1
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Old 02-17-21, 01:47 PM
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You might get a set of vinage MAFAC cantilevers to work. I've found the extra adjustability in them sometimes helps.

The major advantages of going to 700c are the larger selection of quality tires, higher quality (re: more expensive) availability, and wider ones more available than 27". If you want to keep your costs down, stick with 27"
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Old 02-18-21, 10:34 PM
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Are the drop outs vertical or horizontal?

I think those are the same shimano brakes I have on a 93 vintage bike. How many 27" bikes where sold in 93?.

Its hard to tell whats going on with a bike with history till you get a good look. I picked up a mechanic special with all sorts of eclectic parts. What i didnt pick up on was the 700c frame had a 27" fork and the front wheel is 700c and the rear 27". The front caliper is maxed out. Everything else on the bike is intentionaly funky, so I should get it rideable as is and give it a chance, incase the builder was on to something.

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Old 02-19-21, 12:31 AM
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I think the photo is somewhat illusory. When I zoom in it appears that the brake pad is actually rubbing the tire right now and adjusted all the way down in the slot. With 27” wheels this simply could not be the case. I think the brake pad is sitting farther from the rim than it appears. Those Cantis are likely open quite wide and we just don’t have the angle to view it properly. Just gonna have to look at this one in person.
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