Tektro CR520 Brake Set-up

For discussions about bikes and equipment.
User avatar
531colin
Posts: 12242
Joined: 4 Dec 2009, 6:56pm
Location: North Yorkshire

Re: Tektro CR520 Brake Set-up

Postby 531colin » 26 Jan 2010, 6:47pm

With my new- found knowledge of Sheldon, Deliquium's brakes look spot on to me. Straddle as low as possible, brake arms set close to the rim by putting the thin spacer between block and arm. And I bet the anchor angle is pretty close to 90deg when the brakes are on.

User avatar
deliquium
Posts: 1990
Joined: 9 Mar 2007, 3:40pm
Location: Eryri

Re: Tektro CR520 Brake Set-up

Postby deliquium » 26 Jan 2010, 7:04pm

I have to say 531colin, the angle is more than I imagined! And I couldn't get the yoke lower anyway.
Current pedalable joys

"you would be surprised at the number of people in these parts who nearly are half people and half bicycles"

MacBludgeon
Posts: 461
Joined: 6 Feb 2009, 4:19pm
Location: Farnborough, Hampshire, UK

Re: Tektro CR520 Brake Set-up

Postby MacBludgeon » 27 Jan 2010, 5:13pm

this thread is very useful, should it be a sticky somehwere, or at least the relevant bits?
nuns, no sense of humour

User avatar
cavasta
Posts: 186
Joined: 26 Aug 2007, 8:28pm
Location: Malvern, Worcestershire

Re: Tektro CR520 Brake Set-up

Postby cavasta » 27 Jan 2010, 8:40pm

MacBludgeon wrote:this thread is very useful...


I wholeheartedly agree. There have been some very useful and interesting replies to my original post, all of which I am extremely grateful for. Thank you to everyone who's contributed.

SilverBadge
Posts: 577
Joined: 12 May 2009, 11:28pm

Re: Tektro CR520 Brake Set-up

Postby SilverBadge » 28 Jan 2010, 12:30am

531colin wrote: 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.

Got it in one. You trade movement for force, the only thing you can play tunes with is non-linearity. The point of wide profile cantis IMO is that initially the leverage is lower and the cable pull is greater (good for closing the gap), further into the pull the leverage improves (straddle to canti arm goes towards 90deg) giving the stopping power required. Low profile cantis start around 90deg and move further away with cable travel, so you get the force when you need travel and travel when you need force.
And none of this explains the discrepancy between drops and hoods application - think it has to be the shape of the lever. A low pivot, as needed for large cable pulls, would probably make things worse. Maybe lower the levers on the bends so that from the bottom you are not pulling from the very end of the lever?

fatboy
Posts: 3283
Joined: 5 Jan 2007, 1:32pm
Location: North Hertfordshire

Re: Tektro CR520 Brake Set-up

Postby fatboy » 28 Jan 2010, 7:58am

SilverBadge wrote:And none of this explains the discrepancy between drops and hoods application - think it has to be the shape of the lever. A low pivot, as needed for large cable pulls, would probably make things worse. Maybe lower the levers on the bends so that from the bottom you are not pulling from the very end of the lever?


Drops vs hoods is down to where you pull the lever and the leverage that this gives you. If you have long fingers it probably makes less of a difference but with short fingers you are nowhere near the end of the brake lever and hence you have less leverage from the brake lever
"Marriage is a wonderful invention; but then again so is the bicycle puncture repair kit." - Billy Connolly

User avatar
CJ
Posts: 2950
Joined: 15 Jan 2007, 9:55pm

Re: Tektro CR520 Brake Set-up

Postby CJ » 29 Jan 2010, 3:22pm

Like HE said, hoods versus drops is a human factor: hoods is just less ergonomic. It works, but not as good, not never. It boils down to drops are not really ideal for touring, but neither are straights and neither is any other handlebar yet invented. Maybe, one day, touring will get a bit of somebody's development and marketing budget, but for now and for most people drops are the least bad option.

The physics of cantis are that if the anchors and pivots all lie in a horizontal line - pure wide profile - straddle length doesn't make any difference at all and the brake has a near enough linear characteristic, i.e x amount of cable moves the pads y distance throughout the range. Actually, to be more precise and take straddle stretch into account. With pure wide-profile the taller the straddle the better, since then it doesn't stretch as much. Back in the days before mountain-bikes started messing with our brakes that was how it was: cantis just worked and worked good.

But raise those anchors into a low profile geometry and straddle angle becomes increasingly critical, with the brake developing an increasingly regressive action, where it does exactly the opposite of what you want: advances slowly towards the rim at first, then faster, with consequently decreasing leverage! Adjusting straddle length can never cure the brake of this, only make it better or worse, but sometimes you have to make it worse by raising the straddle, in order to make the blocks actually get as far as the rim with a lever that doesn't pull enough cable!

When Shimano raised those arms (bless 'em), they recognised what they'd done to the brake and tweaked the design of their levers (for flat bars only unfortunately) so as to pull more cable at the start and then less with increasing leverage. That way the progressive action of the lever made up for the regressive brake. Unfortunately you can't get levers for drops which work like that. You can get some that pull more cable, but without the progression that gives the desired high leverage final squeeze. Plus they're not as ergonomic from the hoods.

Like I said, touring is a neglected activity. Sometimes someone makes somethign that works really well for us, but usually by accident rather than design. Like the CR520 is really made for cyclo-cross.
Chris Juden
One lady owner, never raced or jumped.

tatanab
Posts: 3582
Joined: 8 Feb 2007, 12:37pm

Re: Tektro CR520 Brake Set-up

Postby tatanab » 29 Jan 2010, 4:23pm

CJ wrote:When Shimano raised those arms (bless 'em), they recognised what they'd done to the brake and tweaked the design of their levers.

I have two cantilevers to compare.
CR520 with Campag Ergo levers - adeqaute performance.
Original Shimao Deore wide arm with 1970s Mafac levers - very powerful and controlable.

I brake from the hoods 99% of the time and don't have a problem with the CR520s and Campag; the point of this is simply to note how strong the brake can be with a lever designed for that purpose. Since the brakes are effectively the same then the difference probably lies in the lever. Mafac made centrepull and wide arm cantilever brakes so I assume the lever was optimised. The pivot is clearly in a different position than that on the Campag.

User avatar
cavasta
Posts: 186
Joined: 26 Aug 2007, 8:28pm
Location: Malvern, Worcestershire

Re: Tektro CR520 Brake Set-up

Postby cavasta » 31 Jan 2010, 11:43am

I've now had a week in which to evaluate the changes I made last weekend to my set-up, following the excellent advice I've received to my original post. During the week I've commuted in wet and dry conditions (25 mile round trip) and flown down the long hill (6-10%) from town with my panniers laden with the weekly shop. I'm happy to report the the difference to the brakes' performance is remarkable. They are now so much more responsive and effective. In wet conditions, which used to be a bit hairy from a braking point of view, they are now very self-assured and do what they're supposed to do: namely, slow me down and stop me! Flying down the hill this morning, loaded up with the weekly shop, the improved stopping power was especially noticeable. I am now able to apply the brakes knowing that they'll work straight away.

Once again, I'd like to thank everyone who's contributed to this thread. It's been an interesting and useful read. Cheers. :D

fatboy
Posts: 3283
Joined: 5 Jan 2007, 1:32pm
Location: North Hertfordshire

Re: Tektro CR520 Brake Set-up

Postby fatboy » 1 Feb 2010, 9:46am

CJ wrote:Like I said, touring is a neglected activity. Sometimes someone makes somethign that works really well for us, but usually by accident rather than design. Like the CR520 is really made for cyclo-cross.


Why don't any of the "off-the-shelf" tourers come with these I wonder? Byercycles have started fitting them to their Super Tourist but Dawes et al are still fitting low profile cantis.
"Marriage is a wonderful invention; but then again so is the bicycle puncture repair kit." - Billy Connolly

User avatar
cavasta
Posts: 186
Joined: 26 Aug 2007, 8:28pm
Location: Malvern, Worcestershire

Re: Tektro CR520 Brake Set-up

Postby cavasta » 18 Apr 2010, 12:05pm

Update:

It's been a while now since I made my original posting and for those who found this thread both interesting and useful I thought I'd report back on how things have panned out.

Following the excellent advice that was given by numerous people, I made the following adjustments:

1) Set the yoke as low as possible, to the point that it's almost in touch with the mudguards.
2) Swapped the inner spacers (the ones between the arm and the pad shoe) for the narrowest ones available.
3) Put the tension springs in the middle hole (of the three that are on the fork). I had previously had them positioned in the top hole. This adjustment in itself made a big difference to the rear braking performance.
4) New cables and pads: Shimano Dura Ace brake cable set http://www.wiggle.co.uk/p/cycle/7/Shimano_Dura_Ace_Brake_Cable_Set/5300002575/ (overkill, maybe, but good quality) and Kool Stop V-Brake Dual Compound pads http://www.wiggle.co.uk/p/cycle/7/Kool_Stop_V-Brake_Dual_Compound_Pair_Of_Inserts/5300005946/

Net result is very effective, responsive and confidence-inspiring braking. Thanks again to everyone who contributed.

SA_SA_SA
Posts: 1676
Joined: 31 Oct 2009, 1:46pm

Re: Tektro CR520 Brake Set-up

Postby SA_SA_SA » 24 Apr 2010, 12:10pm

Tektro RL 520 V brake compatible drop bar levers (when used with V brakes) give easy braking from the hoods: because the mechanical advantage is at the brake.
------------You may not use this post in Cycle or other magazine ------ 8)

reohn2
Posts: 32265
Joined: 26 Jun 2009, 8:21pm

Re: Tektro CR520 Brake Set-up

Postby reohn2 » 24 Apr 2010, 5:03pm

SA_SA_SA wrote:Tektro RL 520 V brake compatible drop bar levers (when used with V brakes) give easy braking from the hoods: because the mechanical advantage is at the brake.


I've used these levers on one of the tandems with V's (Deore)+Koolstop D/compound pads and the braking was very good.
Also I found the Tektros were more comfortable than Shimano aero levers.
-----------------------------------------------------------
I cycle therefore I am.

GrahamG
Posts: 163
Joined: 12 Jan 2007, 5:23pm

Re: Tektro CR520 Brake Set-up

Postby GrahamG » 30 Apr 2010, 3:50pm

Thanks for this everyone - I stumbled across this thread before setting up my CR520's last night. Basically I'd put V-brakes onto a Surly LHT frame but no amount of fettling had them working to satisfactory standard with a drop bar set up (using V-brake drop levers), so I thought I'd just go for the best possible canti's. It was nice to just heed the advice from this thread and get them set up 'right first time'.

mark a.
Posts: 1346
Joined: 8 Jan 2007, 2:47pm
Location: Surrey

Re: Tektro CR520 Brake Set-up

Postby mark a. » 8 Aug 2010, 10:20am

I'm resurrecting a thread here, but I've just come across this document which details the mechanical advantage of different cantilever setups (pdf file):

http://www.circleacycles.com/cantilever ... ometry.pdf

To my mind, it's better than the Sheldon explanations (shock!), partly because it talks more about wide-profile cantis (like the CR520 or 720). It has maths but also some handy graphs which explain things really clearly.

My reading of it gives the following notes:

1) Low-profile cantis give better mechanical advantage (MA) but are harder to set up
2) Wide-profile cantis are less powerful, but are more forgiving of set up and brake wear and, because MA is lower, they clear the rim more
3) Aiming for a 90º angle between straddle wire and anchor is not the thing to do
4) The lower the straddle wire the better

The same guy has also created a nifty online calculator so you can put in the details of your own brakes:

http://www.circleacycles.com/cantilevers/

I think I'll be getting my rulers and calipers out later and measuring the Tekro and Kore wide-profile cantis that we've got and sticking the data into that calculator.