Tektro CR520 Brake Set-up

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BigG
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Re: Tektro CR520 Brake Set-up

Postby BigG » 25 Jan 2011, 3:20pm

Deliquium's set-up in the photos up-thread raises a point about traditional cantilevers. It is not always realised that if the straddle connection point on the cantilever is horizontally level with the arm pivot when the brake shoe makes contact with the rim, then the height of the straddle yoke is totally irrelevant. The pull cable, the yoke and the cantilever arm all move vertically upwards by exactly the same amount. It is only if the straddle connection point is above the arm pivot that additional mechanical advantage is gained by lowering the yoke.

thespod
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Re: Tektro CR520 Brake Set-up

Postby thespod » 8 Feb 2015, 11:28am

Hi. I know this is a very old post so you may not receive this. I'm currently trying to complete a similar setup. I have a Dawes Galaxy that I'm building up. However the cr520 appears to be completely incompatible unless I am making a very rudimentary error which is possible, I'm completely new to Cantis. Distance between bosses is significantly different between front and rear which makes me wonder if front and rear cantis should be different geometry. The set I've been set are two identical sets. Only way I can see to fit these to the front is to have the pads with no spacers at all and accept that until they wear a but at the bottom that the might brake poorly and that with no space there's no way to toe in. Any suggestions would be most welcome. I'm thinking about just going with the At50s that came with the frame and chalking this one up to experience.

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deliquium
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Re: Tektro CR520 Brake Set-up

Postby deliquium » 8 Feb 2015, 12:14pm

thespod wrote:Hi. I know this is a very old post so you may not receive this. I'm currently trying to complete a similar setup. I have a Dawes Galaxy that I'm building up. However the cr520 appears to be completely incompatible unless I am making a very rudimentary error which is possible, I'm completely new to Cantis. Distance between bosses is significantly different between front and rear which makes me wonder if front and rear cantis should be different geometry. The set I've been set are two identical sets. Only way I can see to fit these to the front is to have the pads with no spacers at all and accept that until they wear a but at the bottom that the might brake poorly and that with no space there's no way to toe in. Any suggestions would be most welcome. I'm thinking about just going with the At50s that came with the frame and chalking this one up to experience.


Welcome to the forum :)

Maybe your Galaxy is a model from the 80s or earlier?

CR520 cantilevers require modern bosses at aprrox. 80mm centres. Some frames from around the 1980s had bosses at approx 65mm centres - which were for early Dia Compe and other 'old style' cantilevers.
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NewHorizon
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Re: Tektro CR520 Brake Set-up

Postby NewHorizon » 8 Feb 2015, 2:33pm

They come with a selection of varying thickness washers - it can take some time to work out the best combination of these either side of the brake block itself to arrive at a good spacing. Mine are a different make-up front and rear to achieve the same offset from the rim - is this what you are referring to? Make sure you have the concave washer and disc immediately to each side of the brake block.

fluffybunnyuk
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Re: Tektro CR520 Brake Set-up

Postby fluffybunnyuk » 8 Feb 2015, 3:01pm

I spent a day playing with mine trying to get them setup....in the end i took them to a mechanic, and got them done properly...havent looked back since. After they were setup I'd have to say theyre vastly underrated, and have great stopping power.

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CJ
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Re: Tektro CR520 Brake Set-up

Postby CJ » 8 Feb 2015, 5:36pm

Brake pivot centres that are not only closer together but also significantly different front and rear, is another indication of an old touring or cyclo-cross frame. The centre distance varied because fork crowns and steatstay bridges varied in width, but there wasn't much choice of different designs of braze-on and frame builders (mainly interested in racing, who only made the occasional tourer and didn't appreciate the problem) seldom bothered to file them to compensate for that, so it isn't uncommon to find an old frame on which it's difficult to set up old original cantilevers too!

The archetypal cantilevers were actually Mafac, copied by Dia-Compe et al and briefly made by Weinmann after they bought Mafac. This design was intended to be set up with the arms horizontal, the ends of the straddle cable being anchored at about the same level as the pivots. On this design each block has a long rod-shaped mounting stud, that can be clamped at any point along its length so as to set those arms horizontal in spite of variations in pivot centre distance and rim width. But this design of block was also used on the wide-pivot cantilevers designed for mountain-bikes, so is NO INDICATION that a given brake that will fit an old-design frame.

Moving those pivots further apart was a retrograde step, since it makes the block swing downwards more as it moves in towards the rim, so the brake is less efficient and requires more frequent adjustment. This alteration was required to admit a mountain-bike's fat tyre. And mountain-bike brake levers were adapted with a 'servo wave' action to compensate for the regressive action of their new 'low-profile' cantilevers. Then, having degraded our cantilevers and driven pre-low-profile designs (that work better with non-servo-wave, i.e. drop-bar levers) off the market, mountain-bikes moved on to V-brakes and then to disc brakes.

Eventually, since tourists and crossers are the only people still needing this sort of brake, we've got new non-low-profile cantilevers back again. But sadly we seem to be stuck with pivots further apart than we need or really want them.
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531colin
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Re: Tektro CR520 Brake Set-up

Postby 531colin » 8 Feb 2015, 5:55pm

deliquium wrote:..........CR520 cantilevers require modern bosses at aprrox. 80mm centres. Some frames from around the 1980s had bosses at approx 65mm centres - which were for early Dia Compe and other 'old style' cantilevers.


^^^^^^^THIS........put the old AT 50 on the front....CR720 will be fine on the back, where the mounts are further apart, and they squeal less. As you have 2 pairs of AT50, you can use all the best bits.

Brucey
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Re: Tektro CR520 Brake Set-up

Postby Brucey » 8 Feb 2015, 6:55pm

thespod wrote:Hi. I know this is a very old post so you may not receive this. I'm currently trying to complete a similar setup. I have a Dawes Galaxy that I'm building up. However the cr520 appears to be completely incompatible unless I am making a very rudimentary error which is possible, I'm completely new to Cantis. Distance between bosses is significantly different between front and rear which makes me wonder if front and rear cantis should be different geometry. The set I've been set are two identical sets. Only way I can see to fit these to the front is to have the pads with no spacers at all and accept that until they wear a but at the bottom that the might brake poorly and that with no space there's no way to toe in. Any suggestions would be most welcome. I'm thinking about just going with the At50s that came with the frame and chalking this one up to experience.


FWIW if you have two sets of BR-AT50s then you may as well use them (or at least one on the front, anyway, like Colin suggests). I don't think the CR520 will offer greatly improved braking performance, even if you can get it to fit (which I doubt, on narrow bosses).

If you want a modern canti that will fit both 65mm bosses and wider spaced ones, try the shimano CX50 or Cx70 models. These will offer improved power because (when used with a low straddle) they have a higher MA than BR-AT50s.

If you do use the BR-AT50s I'd recommend getting some modern holders/pads that will allow a better choice of pads etc. Clarks CP522 shoes are XTR knock-offs and work well; they will accept any 70mm V type insert.

Like this;

Image

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thespod
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Re: Tektro CR520 Brake Set-up

Postby thespod » 8 Feb 2015, 8:35pm

Thanks for the welcome and I really appreciate all the advice. Yes The bosses do definitely appear the problem and it's certainly a fairly old frame. I've cleaned up the at50s now and have them on so I'm going with them. Can't wait to get it finished up and hopefully this will be the only incompatibility with the parts I've bought. Fingers crossed

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gaz
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Re: Tektro CR520 Brake Set-up

Postby gaz » 8 Feb 2015, 9:11pm

Mounted on AT50 the Clarks that Brucey suggests extend behind the fork blades. If you have narrow forks and wide rims they won't fit.

531Colin recommended Koolstop Cross Pads to me a while back, no such issues (just make sure you buy the unthreaded version).
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Brucey
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Re: Tektro CR520 Brake Set-up

Postby Brucey » 8 Feb 2015, 10:05pm

gaz wrote:Mounted on AT50 the Clarks that Brucey suggests extend behind the fork blades. If you have narrow forks and wide rims they won't fit.


good point re potentially extending between the fork blades but IIRC the worst that usually happens is that you need to deflate the tyre to get the wheel out. Obviously it can vary but often it isn't even the narrowest part of the brake, because the pads are very slim (~7 to 8mm thickness when new, which is the whole point of this design).

For example on a typical slim fork with ~63mm bosses I found these measurements;

- spacing between the blades = ~55 mm.
- spacing between the spring locations on the bosses = ~38mm
- spacing between the (new) long pads with the brake open = ~37mm

in this case you lose a whole 1mm of clearance for wheel removal by having (new) pads that extend between the fork blades, and nothing when the pads are a little worn. I guess if you have fork blades that are less than 40mm apart and a rim that is around 30mm wide then you could end up in a real clash. But for most bikes there is no problem and for the rest simply letting the tyre down will let the wheel out easily enough.

531Colin recommended Koolstop Cross Pads to me a while back, no such issues (just make sure you buy the unthreaded version).


If the brakes work OK with short pads or forward biased pads, fine, but there are reasons beyond choice of pad compound and ease of pad replacement for speccing the longer asymmetric (reverse-biased) ones; the pivots wear less (the force vector is better positioned) and the brakes usually seem to work better.

Note that any 'symmetric' pad will be effectively forward biased when mounted on BR-AT50 brakes because the pad mount is pretty much flush with the front of the pivot boss. The original BR-AT50 pads were asymmetric ones too, but for ideal braking, probably still not asymmetric enough. I have even experimented with reversing the post mount hardware on the BR-AT50 brake arm and this again seemed to improve the brake in some cases.

cheers



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