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 Post subject: Brake drop...?
PostPosted: Sun Jun 09, 2013 9:10 am 
rBoTM Winner
rBoTM Winner

Joined: Fri Jan 27, 2012 10:01 pm
Posts: 229
Location: Nottingham
Could someone please explain why on most older road frames the rear brake drop / clearance is much bigger than at the front?

This makes no obvious sense and means that the front and rear brake calipers are in some cases different models - I have used a medium reach record on the rear of my Mercian and a short reach on the front. This meant buying two sets of calipers to make one good pair!

On my Carlton, I have had to file out the rear caliper to give me an extra 5mm drop whilst the front brake is set at minimum reach....

On more modern frames this is not the case so surely there can't be a technical reason for this?


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 Post subject: Re: Brake drop...?
PostPosted: Sun Jun 09, 2013 9:58 am 
rBoTM Winner
rBoTM Winner

Joined: Thu Aug 07, 2008 11:54 am
Posts: 1061
Location: Derby
Good question.
Was the frame involved built for 27x1 1/4 wheels ?
IMHO this was the allow for mudgard clearance when fitted.
Most modern frame do not allow for m/g clearance.As you stated.

Loads of info here from the late SB.
http://sheldonbrown.com/calipers.html


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 Post subject: Re: Brake drop...?
PostPosted: Sun Jun 09, 2013 8:19 pm 
Retro Guru
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Joined: Mon Sep 24, 2012 9:10 pm
Posts: 669
Who knows?

The framebuilders said: "The brake manufacturers make rear stirrups longer, so we must put the brake bridge higher"
The brake manufacturers said: "The framebuilders put the brake bridge higher, so we must make rear stirrups longer"

I'm surprised this was still going on in 1980. Is there so much difference between front and rear clearances on your Mercian that you cannot use 47-57mm on both? Or are you using 39-49mm and the rear won't quite reach the rim?

I think 60s manufacturers like Mafac and Universal were the last ones to make brakes in this format, and I think it had been going on for a long time before that. I think Campag were the first to break the mould, with the option of a rear 'drop-bolt' for frames made with Mafac/Universal in mind. Some time in the 70s Mafac and Universal followed suit and 'equalised' their stirups too, at least at the top of the range.

I'm not convinced by the mudguard explanation- why would the rear mudguard need more clearance than the front? The only other theory I can come up with is that this was a sort of anti-skid design- In emergency braking, when you yank on both brake-levers without thinking, it might be advantageous to have a rear brake with less leverage to minimise the risk of locking the rear wheel.


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 Post subject: Re: Brake drop...?
PostPosted: Mon Jun 10, 2013 9:55 pm 
rBoTM Winner
rBoTM Winner

Joined: Fri Jan 27, 2012 10:01 pm
Posts: 229
Location: Nottingham
Good theory about the braking power.

On the Mercian I could have got away with the short reach front and rear but the back one would have been at the extent of its travel.

On the Carlton the difference is much more... Lets see what other explanations the experts come up with!


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 Post subject: Re: Brake drop...?
PostPosted: Tue Jun 11, 2013 5:21 pm 
rBoTM Winner
rBoTM Winner

Joined: Thu Aug 07, 2008 11:54 am
Posts: 1061
Location: Derby
Thinking about this whilst out pedalling , amongst other things,,,, the meaning of life......42 .

How about the fact that the wheelbase was longer on most older frames{Apart from race frames} . Would this have effected brake drop on the rear brake.


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 Post subject: Re: Brake drop...?
PostPosted: Tue Jun 11, 2013 6:31 pm 
Old School Grand Master
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Joined: Fri Oct 14, 2011 8:41 pm
Posts: 8247
Location: Cumbria
As torqueless mentioned........who know's ? it was just the accepted practice.

There is no real reason that the brake bridge at the rear had to be brazed at a position to make the drop deeper. Look at the brake bridges for track frames. Room required for a mudguard is the same as the front....

Shaun


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