Actuation Ratio of Brakes

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Valbrona
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Actuation Ratio of Brakes

Postby Valbrona » 18 Sep 2011, 1:40pm

I am told that if I buy a set of Shimano Dura-Ace 7900 brake calipers, they "Must be used in conjunction with ST7900 STI or BLTT7900 aero levers for correct leverage ratio". Now, I thought a brake pull was a brake pull and you only get actuation ratio's with gears. I am a little confused now because I was going to use some fancy brakes with some Campag Record levers.

What are your thoughts on this matter?
Last edited by Valbrona on 18 Sep 2011, 4:31pm, edited 1 time in total.
I should coco.

BigG
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Re: Actuation Ratio of Brakes

Postby BigG » 18 Sep 2011, 4:18pm

The issue is the amount of cable pulled by the lever over its full travel and the corresponding distance of travel of the brake blocks. There is effectively a "gear ratio" between them normally referred to as the mechanical advantage of the system. If the MA is too high, brake force will be good but there will be inadequate brake block travel towards the rim - which must include the flexibility of the complete lever/cable/brake arm system. If the MA is too low, then brake force will be too low. This issue has been discussed ad nauseam in this forum with reference to V brakes, cantilevers and road brakes using different levers. Perhaps Shimano have a new system with yet another mechanical advantage - or perhaps they just want to sell expensive equipment. You are usually safe in using any road bike lever with any road bike brake mechanism. It is combining road bike levers with cantilevers or V brakes that causes readers of this forum so much anguish.

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531colin
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Re: Actuation Ratio of Brakes

Postby 531colin » 18 Sep 2011, 7:06pm

Valbrona wrote:I am told that if I buy a set of Shimano Dura-Ace 7900 brake calipers, they "Must be used in conjunction with ST7900 STI or BLTT7900 aero levers for correct leverage ratio". Now, I thought a brake pull was a brake pull and you only get actuation ratio's with gears. I am a little confused now because I was going to use some fancy brakes with some Campag Record levers.

What are your thoughts on this matter?


Shimano techdocs. http://techdocs.shimano.com/media/techdocs/content/cycle/SI/Dura-Ace/SI_8FN0A/SI-8FN0A-003-ENG_v1_m56577569830746237.pdf say if you use other levers with these dura ace 7900 calipers, the brakes will be "too strong".
There are no similar warnings (that I can find!) in the other dura ace instructions, so I guess Shimano have made the mechanics of these brakes/levers different to all the others.
Shimano, eh? They'll be catching up with Campag. soon in the pure, bloodyminded awkwardness stakes. Bless.

Valbrona
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Re: Actuation Ratio of Brakes

Postby Valbrona » 18 Sep 2011, 7:47pm

Thanks for that link, Colin. I read the phrase "much too strong" as well. And presumably, if you use the latest Dura-Ace STI with older Dura-Ace brake calipers the action would be "much too weak".

That said, common sense would still suggest that all road calipers should work reasonably okay with all road levers, as per the comments of BigGun.
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531colin
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Re: Actuation Ratio of Brakes

Postby 531colin » 19 Sep 2011, 8:39am

I would think it comes down to something like keeping the wheels perfectly true, running the pads close to the rims and going easy on the levers. (Theres somebody on here who reckons to run V brakes with road levers, but I wouldn't do that....jar your hands over a bump, you could accidently lock it up!)
You need to see the calipers in the flesh, from the drawings in the techdocs. I can't see what they have changed to increase the mechanical advantage of these calipers.
Pity its such a dear do to buy the bits and have a play....

Ayesha
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Re: Actuation Ratio of Brakes

Postby Ayesha » 19 Sep 2011, 9:28am

The secret is to operate the brake levers with your index and second finger only. Grip the bars or undersides of the brake lever body with your third and little fingers.

Power is nothing without control.

Valbrona
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Re: Actuation Ratio of Brakes

Postby Valbrona » 20 Sep 2011, 2:34pm

I found this helpful info on the website of the people who make/sell Revl brakes: The Hive offers two rocker options, labeled with the approximate leverage ratio provided by the rocker. The force gain is either "1.3"or "1.4". The 1.3 leverage ratio is appropriate for Dura-Ace™ 7800 and prior, Campagnolo™, and SRAM™ products. 1.4 is for Dura Ace™ 7900, and UltegraSL™/6700. Note: 1.4 can be run on any lever for more rim crushing force, but it may result in a soft lever feel. The point is, you have options.
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531colin
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Re: Actuation Ratio of Brakes

Postby 531colin » 20 Sep 2011, 8:28pm

So is that a mechanical advantage (MA) of 3 to 1 for most calipers, and 4 to 1 for the dura ace 7900 and the other one?
Thats enough to notice, but using the "wrong" pairings should still work to greater or lesser extent. (33% or 25% difference?)
If its MA of 1.3 to 1 and 1.4 to 1 you wouldn't notice the difference. (7or 8 %)
But the bit about "The Hive" and "rockers" has me bewildered!

Valbrona
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Re: Actuation Ratio of Brakes

Postby Valbrona » 20 Sep 2011, 8:53pm

The Hive is a strangely-named American supplier of bike parts - they make Revl carbon brakes, single pivot things that are said to be as powerful as dual pivots. These brake calipers have a 'rocker system' enabling a choice of two settings - 1.4 or 1.3 actuation ratio depending on what type of levers you are using.

Here's the link: http://bythehive.com/revl/
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RRSODL
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Re: Actuation Ratio of Brakes

Postby RRSODL » 12 Jun 2014, 2:24pm

Valbrona wrote:I am told that if I buy a set of Shimano Dura-Ace 7900 brake calipers, they "Must be used in conjunction with ST7900 STI or BLTT7900 aero levers for correct leverage ratio". Now, I thought a brake pull was a brake pull and you only get actuation ratio's with gears. I am a little confused now because I was going to use some fancy brakes with some Campag Record levers.

What are your thoughts on this matter?


I know this is a very old post but I think it's worth adding my experience for the benefit of others looking for the same information I guess.

I have on one bike the very same combination you were thinking about, Campagnolo Record levers and Shimano Dura-Ace 7900 calipers and they work fine. I did notice the difference between Shimano 105 and Dura-Ace 7900 but I attributed that to being better brakes :lol: I had no idea there might not be compatible.... besides, I take what manufacturers recommend with a pinch of salt. The brakes are amazing, huge stopping power which you get used to in one hour or less.... I think it took me 10 minutes to get used to the difference in stopping power. Shimano make really good quality brakes so I felt an upgrade to DA brakes would be justifiable and I'm very happy with them. If they didn't cost so much I'd have them in all my bikes.

My bike is full of parts that they are not supposed to work together and that is the way I like it, I put the bike together to suit me.
10 speeds Record levers + 105 FD and 105 RD + SRAM 8 speed 32T cassette + 9 speed KMC silver plated chain + Shimano 105 crankset. All works fantastically well. Never tempted to go to 10 or 11 speeds. A good quality chain cost me £9 and a good quality cassette is £17 :) A good frame with good quality components is all I need and my Van Nicholas Ti frame is one of the best I've ever had.

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foxyrider
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Re: Actuation Ratio of Brakes

Postby foxyrider » 12 Jun 2014, 3:55pm

Why not just buy the Campagnolo brakes? - in my experience much better than the fiddly Shimano units
Convention? what's that then?

Airnimal Chameleon touring, Orbit Pro hack, Orbit Photon audax, Focus Mares AX tour, Peugeot Carbon sportive, Owen Blower vintage race - all running Tulio's finest!

Brucey
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Re: Actuation Ratio of Brakes

Postby Brucey » 12 Jun 2014, 7:46pm

foxyrider wrote:Why not just buy the Campagnolo brakes? - in my experience much better than the fiddly Shimano units


Do they make a Campag brake with a mudguard friendly drop....?

cheers
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Mick F
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Re: Actuation Ratio of Brakes

Postby Mick F » 12 Jun 2014, 7:58pm

Yep.
Been there done that.

I was c1985 Campag Victory (Picolo) originally, and used mudguards. In fact it was Mr Mercian who recommended them to me.

Later, went to 2006 Chorus, and they were fine too.
Now I'm on Athena 2012, and still use mudguards.

This is it with 2006 Chorus.
Bike.jpg
Mick F. Cornwall

Brucey
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Re: Actuation Ratio of Brakes

Postby Brucey » 12 Jun 2014, 8:08pm

Mick F wrote:Yep.
Been there done that.


Yes, with skinny tyres only.... :roll:

Last time I looked Campag brake drops were all quite unsuitable for even (say) truly 28mm tyres and mudguards.

For years people have been fitting long drop shimano calipers to their otherwise campag equipped light touring bikes because of this.

One day they may get it (again; they used to make longer drop brakes.... :roll: ), but I'm not holding my breath.... :wink:

cheers
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MartinC
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Re: Actuation Ratio of Brakes

Postby MartinC » 13 Jun 2014, 8:47am

Brucey wrote:One day they may get it (again; they used to make longer drop brakes.... :roll: ), but I'm not holding my breath.... :wink:

cheers


Yes, a few years ago I emailed Mr Campagnolo to see if they were ever going to this again. They just don't see a market for it. Only in Britain do people (including me) put mudguards on 'racing' bikes. Maybe it doesn't rain anywhere else. I think that they're wrong - I can't see that adding some 57mm drop brakes to one of their groups would create much overhead and there must be some sort of market in the Audax/light touring/training segment. I think their view is that to survive they need to concentrate on the premium end of the racing market and not lose their focus by dabbling in other bits - it's why they ditched all the cheap (Xenon and Mirage) stuff.


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