Tektro CR520 Brake Set-up

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deliquium
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Re: Tektro CR520 Brake Set-up

Postby deliquium » 24 Jan 2010, 10:04pm

This may help?

http://www.sheldonbrown.com/cantilever- ... mechanical

But the 90 degree won't/can't apply to wide arm cantilevers like Tektro CR520?
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531colin
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Re: Tektro CR520 Brake Set-up

Postby 531colin » 25 Jan 2010, 7:41am

Thanks for the Sheldon diagram! The angle he calls "anchor angle" I always set at 90deg. The physics of levers is the same, doesn't matter if we call them V brakes, low profile cantis, wide profile cantis, its a lever, and its being pulled by a cable. It works best when we get the cable to pull from EXACTLY the direction we want the lever to move, then we use all the force in the cable. If we only get the pull direction approximate, we use only a moment of that force. (I think its called "moments of forces" .Long time since I thought about it.)

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Re: Tektro CR520 Brake Set-up

Postby fatboy » 25 Jan 2010, 8:24am

The Tektro instructions are useless. You've done the right thing by moving the yoke position down as this improves mechanical advantage (see the Sheldon Brown link) at the expense of rim clearance. However compared with Tektro Oryx you should have a ton of clearance to play with. I don't think that you could acheive the 90 degrees that Colin is advocating, or perhaps I'm mis-understanding things).

If you are still fed up with the braking then it may come down to stiff cables, stiff pivots, dirty rims and dirty pads, pad toe-in etc. I use CR520s and they are great but with lots of use and abuse things can stiffen up over time and you gradually start to loose braking efficiency. This is always most apparent when braking on the hoods (the least mechanically efficient way of braking).

You should be able to get them to work well; they transformed my bike. In terms of absolute braking power I don't think they are quite as good as the Oryx that they replaced but the benefits are huge. I get good modulation of power, smooth braking and almost no fork judder (which was terrible before).
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deliquium
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Re: Tektro CR520 Brake Set-up

Postby deliquium » 25 Jan 2010, 8:48am

I have Tektro CR720 (same cantilever as CR520 but silver) on my touring bike with drop handlebars - they work very well indeed, much much better than the AVID Shorty's they replaced.

There are a lot of long steep downhills in my neck of the woods and my hands would get very weary braking on the hoods, and neck would ache from braking on the drops mile after mile.

So I fitted a pair of cyclocross inspired "interuptor" brake levers to the tops of the bars. Performance is just as good with either type of lever, and I can descend happily, safely and comfortably admiring the view using the additional levers. It did take some time to NOT immediately reach for the regular levers for emergency stops - but I now appreciate the choice.

They're reasonable priced too, and very easy to fit - AVAILABLE HERE

They would probably get in the way of a handlebar bag.
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cavasta
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Re: Tektro CR520 Brake Set-up

Postby cavasta » 25 Jan 2010, 2:04pm

fatboy wrote:The Tektro instructions are useless. You've done the right thing by moving the yoke position down as this improves mechanical advantage (see the Sheldon Brown link) at the expense of rim clearance. However compared with Tektro Oryx you should have a ton of clearance to play with. I don't think that you could acheive the 90 degrees that Colin is advocating, or perhaps I'm mis-understanding things).


I must confess, I have been wondering how I was going to acheive a 90 degree angle without moving the yoke significantly higher than it was before I lowered it. If I were to do that, as far as I can see it wouldn't square with the advice to have the yoke positioned low. Which is the best option: 90 degree angle (or as near as) with the yoke positioned fairly high or a low yoke and less than a 90 degree angle?

It would be really useful if others who've got the CR520s/CR720s fitted and are happy with their performance could upload some photos showing the set-up.

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Re: Tektro CR520 Brake Set-up

Postby fatboy » 25 Jan 2010, 3:50pm

cavasta wrote:Which is the best option: 90 degree angle (or as near as) with the yoke positioned fairly high or a low yoke and less than a 90 degree angle?


I think, if I've understood Sheldon Brown properly, that trying to get to the 90 degree angle for these sort of cantis will reduce performance rather than improve.
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deliquium
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Re: Tektro CR520 Brake Set-up

Postby deliquium » 25 Jan 2010, 4:42pm

cavasta wrote:
I must confess, I have been wondering how I was going to acheive a 90 degree angle without moving the yoke significantly higher than it was before I lowered it. If I were to do that, as far as I can see it wouldn't square with the advice to have the yoke positioned low. Which is the best option: 90 degree angle (or as near as) with the yoke positioned fairly high or a low yoke and less than a 90 degree angle?

It would be really useful if others who've got the CR520s/CR720s fitted and are happy with their performance could upload some photos showing the set-up.


I too can't see how it is possible to get the 90 degree angle mentioned previously, with the Tektro CR520 and other wide arm cantilevers - they cannot be designed to meet that criteria? Lower profile cantis - yes, it makes sense with those and is easily achievable.

Your latest photo where you've lowered the yoke and rearranged the pads - looks very similar to my set up, which I'm very pleased with.

As I understand it re the Tektro - the arms that the pads attach to should be as near vertical and therefore parallel to the rim braking surface of the wheel? This will of course depend on 1) what distance the cantilever bosses are brazed on, 2) the choice of domed/convex washers one has available/supplied with the brakes, 3) the width of the rims.

Tomorrow I'll take some photos of my CR720s on my tourer. They've only been on there a few hundred miles and as said previously work way better than the low profile Avid Shorty's they replaced.

One further point - it MAYBE the photo size/quality distorting the truth? - but your rim braking surfaces seem to be very worn and concave. If so, that won't help until the pads match their worn profile?

It always seems SO much easier to set up V brakes and roadie dual pivot brakes, and for them to do what they are supposed to - stop the bike well. But perseverance, and often lack of alternatives, can make the well designed and made Tektro CR520 work - personally speaking.

And whilst the flow is here!! I don't think, unless you've got strong hands, braking from on the hoods isn't going to be as good/easy/well modulated as using any levers "properly"?
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Re: Tektro CR520 Brake Set-up

Postby cavasta » 25 Jan 2010, 4:57pm

deliquium wrote:And whilst the flow is here!! I don't think, unless you've got strong hands, braking from on the hoods isn't going to be as good/easy/well modulated as using any levers "properly"?


Agreed! The braking power on the drops - i.e. applying the brakes by pulling the levers - is phenomenal. It's just that, like most people I know, I spend most of my time riding on the hoods.

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Re: Tektro CR520 Brake Set-up

Postby reohn2 » 25 Jan 2010, 6:57pm

deliquium wrote:I have Tektro CR720 (same cantilever as CR520 but silver) on my touring bike with drop handlebars - they work very well indeed, much much better than the AVID Shorty's they replaced.

There are a lot of long steep downhills in my neck of the woods and my hands would get very weary braking on the hoods, and neck would ache from braking on the drops mile after mile.

So I fitted a pair of cyclocross inspired "interuptor" brake levers to the tops of the bars. Performance is just as good with either type of lever, and I can descend happily, safely and comfortably admiring the view using the additional levers. It did take some time to NOT immediately reach for the regular levers for emergency stops - but I now appreciate the choice.

They're reasonable priced too, and very easy to fit - AVAILABLE HERE

They would probably get in the way of a handlebar bag.


Whilst it is a little aside from the main topic I think these levers are worth a mention.They were fitted to the new Cannondale tandem (though the brakes are BB7 discs :D stopping power if ever there was),I find them very good,infact so good and useful I have had to stop using them because the other bikes don't have them and I've found myself reaching for brake levers that aren't there :shock: so it was either only use them occasionally or buy three more sets for the other bikes :? I'm still deciding!


PS,If pointed downward which is the natural hand position (as you would with brakelevers on straight 'bars) theres plenty of room for a barbag
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531colin
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Re: Tektro CR520 Brake Set-up

Postby 531colin » 25 Jan 2010, 7:20pm

OK. so now I've read Sheldon, instead of just borrowing his diagram . I was OK. until he started talking about the reciprocal of the sine of the yoke angle! I have to make a mock-up.

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cavasta
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Re: Tektro CR520 Brake Set-up

Postby cavasta » 25 Jan 2010, 7:34pm

531colin wrote:OK. so now I've read Sheldon, instead of just borrowing his diagram . I was OK. until he started talking about the reciprocal of the sine of the yoke angle! I have to make a mock-up.


Looking forward to hearing your conclusions :D

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Re: Tektro CR520 Brake Set-up

Postby freebooter » 25 Jan 2010, 9:23pm

cavasta wrote:
deliquium wrote:And whilst the flow is here!! I don't think, unless you've got strong hands, braking from on the hoods isn't going to be as good/easy/well modulated as using any levers "properly"?


Agreed! The braking power on the drops - i.e. applying the brakes by pulling the levers - is phenomenal. It's just that, like most people I know, I spend most of my time riding on the hoods.


I think this is cetainly true with drops and cantis, I don't know whether it is better on a proper road bike with caliper brakes.

I read this thread with interest as I have a bike with drops and cantis. I have changed the cabling and fiddled with the brake setup repeatedly with no great improvement. I then tried a Tektro 720 on the front instead of the Oryx that were there and it is a bit better but still not great. I think it is just the weak hand position on the hoods means that it is difficult to put enough force. I have had to stop quickly a few times and when squeezed hard the brakes work well even from the hoods but in normal braking the amount of force needed is uncomfortable.

I have cross levers on as well and they make it much easier to apply the needed force but the hand position is too narrow.

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Re: Tektro CR520 Brake Set-up

Postby 531colin » 25 Jan 2010, 10:02pm

Here is my interpretation of Sheldon. (I wouldn't claim anything except that in this form I understand what he is saying,)
Sheldon says
The mechanical advantage of a canti brake has 3 components;
1...Cable pull of lever (we got that one)
2...Getting the "anchor angle" to 90deg. We got that one as well, but Sheldon regards it as an over simplification, in view of......
3...The closer to straight the straddle wire is, the greater the mechanical advantage.
This is the bit I mocked up and checked. I can't check force, but in physics there is no free lunch, a system with a high mechanical advantage gives a small movement. So I found when I moved my mocked up brake cable 1cm. with a straight-ish straddle, the straddle ends moved much less than they did moving the same 1cm. with a long, bent straddle.
SO, the lower the straddle, the better the mechanical advantage - some of you guys got that one, too, but I have learned something to-day, so thanks for that!
Sheldon also infers that the straddle wire effect is greater than the 90deg. anchor angle effect, so set the straddle bridge low in preference to chasing the 90deg.
(but choose brake block spacers to get as close as possible to 90deg.)

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deliquium
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Re: Tektro CR520 Brake Set-up

Postby deliquium » 26 Jan 2010, 3:36pm

Here's photos as promised. I can't imagine getting better out of this set up. Although this is the only bike without Koolstop salmon pads - but I don't feel the need to change the original Tektro ones, as the bike stops very well (haven't tried it fully loaded with panniers etc). But I'm puzzled now as to why the cable clamp triangle is so skew-whiff - must investigate/tinker!?

Interesting to note, that either the wheel isn't centred in the forks, or the canti bosses aren't quite aligned properly.

Also worth a mention is the brake cable hanger which cured the most almighty fork brake judder known to humanity!

Shame about the cable mess too!

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Re: Tektro CR520 Brake Set-up

Postby fatboy » 26 Jan 2010, 3:51pm

I forgot to say.....another thing that I did to improve braking was to remove the cantis and put the spring onto the weakest setting. I figured that so long as they return OK (which they do) having extra spring is taking power from my hand to rotate the springs rather than to brake. It seemed to help a bit. I've just ordered a replacement light bracket that should allow me to lower the yoke some more for further extra power (I hope); I can't lower it to the level that deliquium has as it would foul my light.
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