Narrow forks with canti brakes?

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jackt
Posts: 38
Joined: 30 Jul 2008, 11:13pm

Narrow forks with canti brakes?

Postby jackt » 22 Sep 2014, 11:35am

I'm looking for some advice.

I've a Roberts light tourer with quite a narrow fork crown, and canti brakes. The fork is so narrow that the long canti brake shoes/pads don't fit in the space between the fork crown and the wheel rim, so thus far I've been fitting shorter caliper style pads, which is not really optimal.

Is it possible that the rim is too wide, reducing the space for the brake pads? The frame just about takes 28mm tyres with muguards, and this would be my preferred tyre width. Should I be looking for a narrower rim? What is the narrowest rim that'll accept 28mm tyres?

Or is the problem in the canti brakes? Currently Tektro CR720.

Any tips or advice much appreciated.

Jack
Author of Lost Lanes, Lost Lanes Wales and Lost Lanes West. Presents The Bike Show podcast.

tatanab
Posts: 3788
Joined: 8 Feb 2007, 12:37pm

Re: Narrow forks with canti brakes?

Postby tatanab » 22 Sep 2014, 11:44am

I would simply stick to using short brake blocks as you are doing. This is the way things were before long skinny MTB V brake parts and so on.

I seem to remember that in theory the length of the brake block makes no difference to braking, except perhaps for cooling.

Narrow rim to take 28 tyres is something like a Mavic Open Pro.

Brucey
Posts: 36097
Joined: 4 Jan 2012, 6:25pm

Re: Narrow forks with canti brakes?

Postby Brucey » 22 Sep 2014, 12:18pm

worth looking at all the various long pads that are out there; some are a lot slimmer than others. If you do succeed in fitting long pads, you will likely find that you can't get the wheel out without deflating the tyre (which isn't a complete disaster).

My suspicion has always been that long brake pads work better because they skew less under load. Short pads therefore do less well with unaccustomed braking loads; typically when you really need them the extra force causes the pad to skew more than normal, this reduces the contact area still further and then the brake goes away because the pad overheats locally... or something....

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

jackt
Posts: 38
Joined: 30 Jul 2008, 11:13pm

Re: Narrow forks with canti brakes?

Postby jackt » 22 Sep 2014, 8:02pm

thanks both - very helpful
Author of Lost Lanes, Lost Lanes Wales and Lost Lanes West. Presents The Bike Show podcast.

LuckyLuke
Posts: 226
Joined: 10 Jun 2010, 11:54am

Re: Narrow forks with canti brakes?

Postby LuckyLuke » 22 Sep 2014, 8:11pm

Hi Jack,

What's the distance between the brake bosses? ~80mm is the current norm. I've had / have frames with 65mm and 55mm gaps between bosses, and modern V brakes and canti's (like your Tektro's) don't fit. These use 'threaded' brake pads and they jut out from the brake arm too much for the narrow fit.
Older cantis and one or two early V brakes do fit, if the brake arm uses the 'smooth post' or unthreaded brake pads. E.g. Shimano BR-MT60 cantis, or Shimano STX RC V brakes.
See pictures from 531 Colin halfway down the page:
viewtopic.php?f=5&t=52762
The unthreaded brake pads can be butted right up against the brake arm, allowing a tight fit.

Koolstop Thinline smooth post pads also work well if you've a tight fit:
http://www.koolstop.com/english/thinline.html

Best wishes,

Luke

jackt
Posts: 38
Joined: 30 Jul 2008, 11:13pm

Re: Narrow forks with canti brakes?

Postby jackt » 30 Oct 2014, 4:44pm

Sorry for the delay (frame was in for repair and repaint)... distance between the brake bosses (centre to centre) is 72.5mm. Which I guess is less than the standard 80mm, but not as narrow as some.
Author of Lost Lanes, Lost Lanes Wales and Lost Lanes West. Presents The Bike Show podcast.

Brucey
Posts: 36097
Joined: 4 Jan 2012, 6:25pm

Re: Narrow forks with canti brakes?

Postby Brucey » 30 Oct 2014, 10:56pm

you can use quite narrow rims with 28mm tyres and this would help somewhat. You can check rim manufacturer's specs to see what they suggest; often you can find a rim that is basically the same shape as a rear rim but skinnier and this will give a 'matched pair' well enough for most folk.

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