cstar 

Ok, so I've always wondered about this and never been able to find an answer. You find tons of classic and vintage bikes with a longer reach rear caliper than front caliper. Dia compe 750 rear and 610 front comes to mind as the usual culprit combination.

Why is this? Did it have to do with some theoretical effect on frame flex by having the rear stay brace higher? It just seems like having two identical calipers would make a lot more sense

Not the most profound question I realize, but I would love to know the reason behind it.

T-Mar

If you have two calipers of the same reach, a newbie will apply each with the same force, resulting in rear wheel lockup and increased braking distance. In the 1970s, the vast majority of riders were new to caliper brakes and had this issue. Longer reach calipers have more flex and less mechanical advantage, making it less likely to to lock the wheel. Most entry level bicycles came with unequal reach brakes. Equal reach brakes were typically the domain of higher end racing models, intended for more experienced cyclists, who presumibly knew how to modulate the brakes.

Longer reach calipers also provide extra clearance for fenders. During the early 1970s bicycle boom, even high end racing bicycles had fender eyelets and medium reach calipers to facilitate fender installation. Not many people could afford a separate training bicycle, When it rained you slapped on fenders and a set of training wheels and rode anyways. You had to get used to riding in the rain, especially in Europe, because a lot of early and late season races would be be wet.

Later in the boom, some of the European builders started building with tighter clearances in response to their pro cyclists' demands. This lead to the development of short reach brakes and the gradual elimination of medium reach racing brakes and associated fender eyelets on droputs. Like most developments, it would slowly trickle down to mid-range sports bicycles.

However, the concept of tailoring the stopping power for front and rear brakes was not dead. In the early 2000s Campagnolo offered "differential" brakes that had the same geometry for the front and rear but the rear was made lighter (i.e. flexier) to reduce lock-up.

79pmooney

And along those lines (less stopping power in back), the full length housed brake cable runs along the top of the TT in the '80s. Campagnolo's dual pivot front and sidepull rear. And my two city bikes, both set up Mafac RACER front and Weinmann centerpull rear. Mafac to get the stopping power where needed and the lass powerful but sitter feeling Weinmann to offset the spunge from the cable runs. (That setup feels identical to the hands but doesn't lock up, even in very hard stops; And both bikes are stoppers! I take the front Weinmann and rear Mafac of a set of each and buy quality hardware bolts of appropriate size to convert it for the other end of the bike.

cstar 

As usual, you are a wealth of knowledge, what would we do without you?

One of my theories was just that, making the rear brake less easy to lock

Thank you as always !

cstar 

I love every bit of this! I have often also wondered about the full length rear cable given the extra weight over cable stops and bare cable and the spongy feel. As someone who can modulate and as someone with some mechanical knowledge I've always been baffled by these features, but then again I also love stopping power. Thanks for inadvertently solving that for me as well. Any other peculiarities of bike design that you care to casually demystify? 🙂

I love your philosophy about the mix and match of the MAFAC Racer and Weinmann. I have considered doing that simply because I adore the Racer but my application requires a 750 rear for reach... I'm definitely going to do that now, and now I'll have a good reason to do it.

As a bit of a tangent. I always wondered why the Weimann used aluminum nuts on the brake pads but not for the mounting bolt. I understand there's probably more stress on the mounting bolt nut than the pad nut and I see the wisdom of the steel nylock nut they used on the mounting bolt, but... Could you use an aluminum pad nut with a drop of loctite on the mounting bolt or is it just not strong enough?

Thanks again

79pmooney

I'd pass on that aluminum nut on the mounting bolt. In front, that bolt is all you've got between you and the car that just stopped in front of you. Nut strips off, rim/brake pads will just whip that bolt right out. (Now, in back, the rim/brake pads will try to bend the bolt down; much harder. The brake pads are held primarily in sheer on a Weinmann style caliper. The nut really doesn't do much

cstar 

That makes perfect sense, thanks! Guess a nice chrome or stainless acorn nut it is, then

Charles Wahl

I agree with everything that's been said, but in practice, things are not so simple. Here's a sampling of actual bikes, measured by me:



Note that a few have greater reach in rear than front, a few are equal, and a surprising number have greater reach in front than in rear (usually those that weren't designed to be equipped with fenders). They're essentially in chronological order here.

cstar 

Wow, I love the dedication in this

What I originally was referring to is bikes originally spec'd with a much longer rear caliper than front, done so intentionally. Which seems to be a feature of cheaper 70s boom bikes, done for the reasons others explained (to help novice riders)

If I'm reading that chart correctly, it strikes me that your bikes at large have very similar axle to brake mounting bolt distances F and R. Which adds up with what others said regarding higher end bikes typically using the same reach caliper F and R, since you're stuff is nicer than say, my boom Windsor Carrera Sport

My Raleigh Super Course is an exception too, absurd space in front fork, rear brake needs less reach

repechage

the "differential" caliper sets I saw had a dual pivot front and a single pivot rear.

The very early differential leverage as earlier noted was effected by reduced mechanical advantage by "lever arm length"

Charles Wahl

Your appreciation is appreciated. It's a lot more extensive than what's shown; I collapsed a lot of columns to get to the brake reach/tire clearance info: weights, angles, tubeset, seatpost dia., even spacing of the pump pegs for ones that have those.

79pmooney

A note on my love of full length housings - TiCycles has built me two custom frames. They put the usual cable stops at the normal location near the TT ends. Stops to end the housing and run bare cable. The stops have a slow at the top so cable removal is easy. I said "no"; that I wanted full housing guides a la '80s. Well they have guides that an insert fitted into so they could be retrofitted to the modern bare cable run. "No, just plain old guides please." I got them. Second bike wasn't so hard. They remembered that conversation!

The funny thing is that the bare cable run and slotted stops on the second bike (my avatar photo) would have saved me work many times. I have two separate "cockpits" for the bike; a traditional road setup running to a pair of sweet Superbe brakes and the climbing setup with wide and deep pista bars, huge V-brake road levers my hands love and dual pivots. Everything stays hooked up. I just undo the brake bolts, slice the brakes off, loosen the quill stem and lift. Except that rear brake. Gotta undo the cable clamp and pull the housing out of those old-fashioned housing guides. Still, the swap is pretty darn easy. 5 minutes maybe. No critical attachments or adjustments. (Yes, the rear brake every time but it has a good working cable adjust and the cammed QR that stays at any setting I leave it at. Plus, it's just a dumb rear brake, dumbed down further with the full length cable guide.)

My Raleigh Competition has housing stops on the lower DS of the TT. They are still there but I've never used them. Housing runs along the TT just to the left of center (on that bike, the housing bends are less) with some nice clamp-on guides I picked up. And of course my bikes of '79 and early eighties all have full length runs where they belong.

Another plus of full length runs on one talks about. You can pick the bike up by the top tube and never scrape the paint. Sit the bike down on hooks under the TT. You can also sit on the top tube. (Look at any pre-race photo of the pros. Many have their butts or thighs parked on the top tube while their fellows line up behind them.)

And, full run housings have two fewer cable exits to allow entry of water, development of kinks, etc. (The forward one is subject to far more housing movement than any other on the bike, what with the handlebar swing. And both are fully in the elements unlike at the brake lever where it is pretty well protected and at the brake where the housing is pointed down, discouraging water from getting very far.)

63rickert

Small frames and horizontal top tubes. Stock lugs with limited angles. Headset stack. Think about it a minute. If there is lots of air above the front tire the top tube is inevitably higher. The smaller the frame the more little details have to be watched and fudged to get the top tube down to where the short customers can stand over it. There was reluctance to build with too short head tubes and short little steerers. It is good engineering to avoid a front triangle that comes to a point. Practical necessity or perceived practical necessity. The job has to get done in a factory that was fairly primitive .The rear brake is the normal brake that easily swallows fenders. And that 27" wheel those crazy Americans demand. Once it is a mixed set of brakes on the small bikes cheaper to order the mixed set for the whole range.

In earlier eras the small frame was not that small and short customers just had to cope. When factories started making small frames for small people there were problems and the solutions not always elegant.

63rickert

I'm going to push it a little further. The business about weaker brake in the rear is latter day lawyer speak. And American lawyers. I can't imagine anyone in St. Etienne in 1960 or 1970 having any patience with that line of reasoning. They would all have vivid memories of attempted downhill braking on pre-Mafac brakes. The whole concept of designing machinery for adult children who have never learned how to ride and are not willing to learn how to ride did not yet exist.

My 1950 Bates is equipped with Weinmann 999-750 brakes front and rear. The pads are at lower limit. Granted the 1959 version of that brake is a little nicer than subsequent production. They were there when I got the bike and they aren't going anywhere. With those weak flexible brakes I have repeatedly outperformed DuraAce hydraulics. It is not because the 750s have more ultimate power. They do not. It is because the greater part of successful braking is the person operating the brakes. It is not what you ride, it is how you ride.

John E

The other benefit of a longer-reach rear is that it closes faster, making it more tolerant of cable stretch / housing compression.