the 'full size V-brakes'.... that weren't...?

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Brucey
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Joined: 4 Jan 2012, 6:25pm

the 'full size V-brakes'.... that weren't...?

Postby Brucey » 18 Oct 2015, 9:22pm

I've been messing about with another project bike recently. It came to me as a frameset, with very few parts attached.

It would originally have been fitted with cantilever brakes, and the frame accordingly has a brazed-on hanger for the rear brake. The front brake would have been fitted via a (special) bolt-on uphanger, which is sadly missing. The frame needed a lot of work, (including a weld repair, rectifying completely seized suspension, and dealing with a seized -and difficult to replace- seat-pin) all of which I've managed to complete over the last week or so.

So having sorted out the frame so that it can be built up, I thought I'd build it up quickly so that I can see what it is like to ride. I've fitted the correct size wheels, with a two-speed automatic coaster brake at the back, and went to fit a rim brake at the front. 'Easy job...' I thought, ' ....I'll just stick a V brake on there'. So my carefully stashed set of unused Avid single digits came out and on they went. I was even careful to set the brake lever to the 'V-brake setting' before I fitted it.

But then I hit a snag; for some reason I couldn't easily adjust the brake pads high enough in the brake arm slots. I checked the brake arms and they were perfectly normal in terms of the adjustment on offer. I checked again that the correct size of wheel was fitted, and even that there wasn't another (smaller) rim size that could possibly make the brakes fit any better. I reckon that the rim centreline is ~42mm above the canti-boss centre line; to get these brakes (indeed most Vs I reckon) to work at all, the pads are at the top of the slots and they must be angled upwards too!

Now the arms are 100mm long or so (just like most Vs) but the caliper MA is now nearer 2:1 than the usual 3:1 or even 4:1 that is more often seen with these brakes. Needless to say with the lever set to 'V' setting the brakes were wooden and useless. I changed the levers back to 'canti' setting and I have something that is more like a brake.

Another side effect of this is that with 2" tyres fitted, the noodle only just clears the tyre, a bit like you find with some Mini-V setups. If I fit mudguards, I reckon I have about 10mm total for the mudguard and clearance above and below it....which isn't enough. The frame has another 5-10mm clearance than that. The rear brake will fit the same way because the bosses are similarly positioned.

Now I daresay I can file out the brake arms a bit and maybe find a slightly longer full-V brake of some kind, and maybe this will allow me to fit Vs. Weirdly, I reckon I'll be able to use road STIs or brake levers with them and they will be fine. So I'm not in a total cleft stick.

But this does leave me with a few questions;

1) has anyone else seen this kind of thing? (I've previously only ever seen a few frames that used much over 30mm boss to rim height, and if cost were any guide, I'd be surprised if it were a mistake on this one. The frame would have been designed around 1993 and manufactured around 1996 I think, i.e. just predating common use of V brakes).

2) I wonder how on Earth I can fit cantis so they work? I think that the MA will be very low unless I do something clever. At the front I can tolerate wide arms, but I can't get the straddle very low (fat tyres plus mudguards...) and at the rear part of the suspension means that I can't get the straddle low there either, it'll be about +40mm above the mudguard, even... I can't get the MA back again easily because wide arms are going to be a heel clearance issue.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

gregoryoftours
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Joined: 22 May 2011, 7:14pm

Re: the 'full size V-brakes'.... that weren't...?

Postby gregoryoftours » 18 Oct 2015, 10:58pm

I've not heard of that problem before. I don't know if the some of the style of cantis or v brakes where the arms are cylindrical rods would have more vertical adjustment than usual, would they? I mean something like avid tri-aligns or something like this - http://www.btt.com.ar/mtb/569600-tektro-cantilever

http://www.ebay.ie/itm/Tektro-865a-Ligh ... MeoY27zDoA

there are other retro types I can't remember. But I think that these low profile types would have really bad m. advantage. I guess what would be best is some wide profile cantis that have a lot of vertical adjustment and are extra wide to provide the needed m.a. If you could get a v brake that fits you could still use a canti lever to compensate for reduced mechanical advantage. Even if this did work to some extent the tyre clearance problem is still there I guess.
Last edited by gregoryoftours on 18 Oct 2015, 11:19pm, edited 1 time in total.

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531colin
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Location: North Yorkshire

Re: the 'full size V-brakes'.... that weren't...?

Postby 531colin » 18 Oct 2015, 11:14pm

What frame is it? What brakes were fitted originally, were there ever brakes with longer arms?
If front and rear are the same, frame damage seems unlikely....have the bosses been moved?

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531colin
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Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: the 'full size V-brakes'.... that weren't...?

Postby 531colin » 18 Oct 2015, 11:16pm

gregoryoftours wrote:I've not heard of that problem before. I don't know if the some of the style of cantis or v brakes where the arms are cylindrical rods would have more vertical adjustment than usual, would they? I mean something like avid tri-aligns or something. there are other retro types I can't remember. Probably they don't but I'm not sure. If you could get a v brake that fits you could still use a canti lever to compensate for reduced mechanical advantage. Even if this did work to some extent the tyre clearance problem is still there I guess.


Like these Tektros......

Image

but if you put the pads high up the arms, bang goes the MA.

gregoryoftours
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Joined: 22 May 2011, 7:14pm

Re: the 'full size V-brakes'.... that weren't...?

Postby gregoryoftours » 18 Oct 2015, 11:36pm

531colin wrote:but if you put the pads high up the arms, bang goes the MA.

Yes, what you really want is wide profile cantis that have enough vertical adjustment to reach the rim, and extra wide to compensate for the reduced MA. You'd get clearance then too.

Brucey
Posts: 36763
Joined: 4 Jan 2012, 6:25pm

Re: the 'full size V-brakes'.... that weren't...?

Postby Brucey » 19 Oct 2015, 10:03am

531colin wrote:What frame is it? What brakes were fitted originally, were there ever brakes with longer arms?
If front and rear are the same, frame damage seems unlikely....have the bosses been moved?


I'm pretty sure that the bosses have not been moved. The frame is a Moulton APB, (so a Pashley-built one, probably an APB-3 or an APB-5 originally judging from the braze-ons but I can be sure, frame number in the 1200s so an early-ish one). I guess the rear clearance will vary a little with wheel adjustment anyway; however with a post-mount brake the rear would have slightly different clearance, because the pads are set backwards and the wheel is at such an angle to the stays, but the front clearance will be little altered regardless of brake type, because the wheel runs through the fork pretty much at a right angle. I think the fork is original because the dropouts are stainless steel; apparently later APBs had different dropouts.

I've scoured the internet for photos of similar bikes and those with the braze-on rear hanger (like mine) had cantis fitted, looking mostly like dia-compe low profile ones (which do have long arms IIRC.... but the specs I have seen list shimano TY22...?). Unfortunately close-up photos are few and far between, but even so some of them appear to have the brake bosses set like mine and others less so. The majority of APBs came without the rear hanger and were (or have subsequently been) fitted with V brakes, it seems.

BTW it occurs to me that although the wheelbase is about the same as a conventional bike, because the wheel radius is smaller, the amount of effort required to send you over the bars is less than with a normal bike; [once you get to (say) 45 degrees, a larger wheeled bike would have everything about 4" higher up] so perhaps it was deliberate....?

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

LWaB
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Joined: 26 Nov 2010, 5:33am

Re: the 'full size V-brakes'.... that weren't...?

Postby LWaB » 21 Oct 2015, 6:35am

Not all APBs used 406 wheels, some used larger diameter rims. From memory, the unusual ones were hub-geared.

Those Tektro cantilevers are copies of early Onza brakes.

Brucey
Posts: 36763
Joined: 4 Jan 2012, 6:25pm

Re: the 'full size V-brakes'.... that weren't...?

Postby Brucey » 21 Oct 2015, 7:44am

I did wonder about different rim sizes but a smaller rim would make the brakes fit better, not a larger rim.

There are (were...?) rims at 387, 390, 400mm sizes but these appear to be more or less obsolete and I can't find any reference to them having been used on moulton APBs.

I wonder if it isn't just erratic jigging in the factory. This photo;

Image

shows a TSR front brake, and here they have gone the other way; the pads are in the bottom of the slots!

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~