Charles Wahl

I've wondered why there is typically more brake clearance (reach) on the rear, than on the front, on older frames built for centerpull brakes like Weinmann and Mafac. For instance, the front Weinmann for many such frames has a max. reach of 61 mm (model 610) while the rear goes to 75 mm (750). And the frames require more reach on the rear than in the front.

Anybody?
Thanks,

cyclotoine

it is curious, my jeunet has a standard reach (1970s) campy sidepull on the back and a short reach campy sidepull on the front.. I put them there.... i was suprised when I found I could not use the standard caliper on the front. hadn't given that much thought to it though...

unworthy1

good question, and I don't have a good answer...but I am pretty sure you can find this "unequal" brake feature on some period Italian frames, too.

el twe

My Schwinn Super Sport was the same way.

frameteam2003

Maybe ,cause front wheels are always mounted in the same location where as rear wheels can be moved a bit in the drop outs?

John E

If I recall correctly, English, Austrian, American, and Japanese bikes with Weinmann 999 centerpulls all indeed tended to use 610 brake calipers in front and 750s in back. However, the front and rear brake reaches on Peugeot UO-8s of the same vintage were more nearly equal.

A longer-reach caliper will provide slightly less grab leverage than a shorter one, and it will begin to engage a bit more quickly. frameteam2003's observation regarding wheel position has some merit, as well, but I have yet to read a truly definitive explanation for the front-rear disparity. The late Sheldon Brown's glossary defines brake reach and tells how to measure it, but gives no clue to solving our mystery.

hhabca

I like the brake balancing idea - a way to limit braking on the rear wheel. Could it also be they assumed owners wanted to put larger tires on the rear because it was more heavily loaded? Was that a recommended practice back then?

Or, they got a warehouse of Weinmann 750 brakes really cheap and just built frames to fit them, having already built the forks for the 610s!

gridplan

I asked Bob Hovey about this a year or two ago. He wondered if it had to do with rear fenders, saying rear fenders had more clearance so that you could slide the wheel forward to remove it.

redneckwes

I allways just figured that Weinmann sold the 610/750 together, so they made the frames to match

nlerner

Isn't it an indication of fairly long chain stays, resulting a long wheelbase and the "touring" ride so typical of those late 60s and early 70s road bikes?

Neal

martl

Yep you can, my 1951 Girardengo is built like this.

John E

The typical long dropout slot is a probable partial explanation, but why did Peugeots tend to use calipers with equal or near-equal reach?

rhm

My 1983 Trek 720 Tourer is built the same way. More brake clearance in the rear than in the front, with the result that standard reach caliper brakes fit either 27" or 700C rim in front, but only 27" rear. To fit a 700C wheel to the rear, I had to get longer brakes (or Campy drop-center bolts).

dbakl

Got any pics to post of the Girardengo?

Noah Scape

I've always figured this was the reason... makes sense to me.

unworthy1

I've decided to face the flames and ridicule of the CR list by asking them this question, I'll report back on what they say.
Don't worry about me, I can take it: I've already heard Chuck Schmidt yell at me to "Check the Archives!!!" inside my head.

Charles Wahl

Why not check the archives first? I realize that it's a complicated thing to query effectively by a few keywords.

Thinking over the replies here, it occurs to me that I have a very short-coupled racing frame (74 degree seat tube, 41 cm chainstays, wheelbase less than a meter) with short reach brakes and horizontal rear dropouts (though not long ones like the Campy 1010) -- and I have no trouble getting the rear wheel out.

So my money is on it having something to do with the combination of fenders and a longer rear dropout. The "depowering" of the rear versus front is an elegant and imaginative theory, but doesn't seem likely to me.

Citoyen du Monde

In the CR archives you will indeed find a few answers, some of them already listed here. The getting the wheel out is the main reason. I don't believe the brake reason would stand up to engineering muster. In Italy at least the bikes with the biggest brake caliper arm length difference were made in the period of the cambio corsa and paris-Roubaix gear, both used incredibly long rear drop-outs. As the dropouts shortened, so too did the brake caliper arm lengths.

unworthy1

Well I DID check the CR archives first, I know better...but you have to hit on just the right combination of words to get results for a topic like this, and it's a crap-shoot: it ain't Google.
The upshot of my query is that most RECENT responders don't know *for certain* why, either. But they did offer answers:
1. to allow for fender/mudguard clearance
2. to allow for a wider tire in the rear (apparently at least one rider does this)
3. to allow for easier rear wheel removal
4. to reduce brake power to the rear and prevent rear brake "lock-up"
and the 4th is fairly popular...whether you accept the engineering principals behind it or not is up to you, I'm just the messenger here.

Charles Wahl

Thank you, unworthy1. Your exertions are much appreciated.

T-Mar

That was always my understanding on the situation. I don't buy into any of the others. Under braking, when the rim clamping energy exceeds that of the turning wheel, inertia transfers the weight to the front end and the bicycle and rider pivot on the front tire's road contact point, unloading the rear wheel and making rear wheel lock-up easier. In extreme cases, the rear actually leaves the ground and you can go over the bars. To counter-act in emergency situations, riders will extend their arms and push their butt as far past the saddle as possible, to bias as much weight as possible to the rear. About a decade ago, Campagnolo readressed the problem with their "differential" brakes. The rear was manufactured lighter and more flexible to reduce the chance of lock-up.

The only perplexing thing about the differential length brakes was that they were found on entry level models, which were heavier, longer, with more rearward weight bias and tended to be ridden slower, all which result in less tendency to unload the rear wheel than a competition model. So, you would think that this concept would be more useful on competition bicycle, however manufacturers were assuming that racers and avid cyclists had intuitively developed the skills of differential braking through experience.

Of course, the ideal would be have brakes that worked on the concept of absorption of inertia, just like Bessie in Doctor Who. Then we could all stop on dime and wouldn't need seat belts or air bags in cars. Mind you, we would all need lightning quick reflexes or give a lot more room when following other vehicles.

martl

Very few..
its family heritage, my uncle bought it new Him and then my dad used it until the mit 60ies, then it rotted away in the basment. It also must have crashed one day badly, both upper and lower tube show it. My dad had it straightened and refitted with mid-level stuff in the late 70ies, at that time all the original simplex stuff apparently ended in the bikeshops trashbin.
Then i found it and had it reworked to make a tourer of it, with some braze-on work of shifter sockets and other details. it also underwent a rechroming and repainting at the Patelli factory. Unfortunately, it's "italian finish" in the worst way. But it served me well a couple of years as a tourer. I plan to restore it, some day...



pics are on https://www.tourgalerie.de/cpg132/thu...s.php?album=15