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 Post subject: Chainstay UBrake.. Why??
PostPosted: Fri Nov 24, 2006 5:48 am 
98+ BoTM | BoTM | Gold | Rider
98+ BoTM | BoTM | Gold | Rider
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Joined: Thu Mar 23, 2006 12:48 am
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Location: Kingdom of Ringlé
Just been checking out EBay US and came across a few 80s rigs on there.. The more I looked, the more I began to wonder..

Why put the rear brake under the chainstay? Who's idea was it?

Image


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PostPosted: Fri Nov 24, 2006 6:44 am 
Retro Guru
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Location: leicester
dunno but thats a roller cam not a u brake :lol:


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 Post subject:
PostPosted: Fri Nov 24, 2006 6:52 am 
98+ BoTM | BoTM | Gold | Rider
98+ BoTM | BoTM | Gold | Rider
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Image

Hahahaha :P

Quote:
Why put the rear brake under the chainstay?


:wink:


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PostPosted: Fri Nov 24, 2006 7:01 am 
Dirt Disciple
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Joined: Fri Jul 22, 2005 2:50 pm
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kingroon wrote:
Just been checking out EBay US and came across a few 80s rigs on there.. The more I looked, the more I began to wonder..

Why put the rear brake under the chainstay? Who's idea was it?

Image

I think the idea was the stiffness under the chainstays.There was less flex!
Later they change to seatstays,because it's a better protected spot against mud.

Olli :P


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 Post subject:
PostPosted: Fri Nov 24, 2006 10:03 am 
Old School Grand Master
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Location: No brakes? Way to commit soldier.
I'm pretty sure that U-brakes were put down there purely because it got them out of the way and the rear end of the bike looked neater without a bloody great brake perched over the rear wheel.


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PostPosted: Fri Nov 24, 2006 10:04 am 
B.o.T.Y. Winner / Gold Trader
B.o.T.Y. Winner / Gold Trader
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from the sheldon brown glossary :arrow:
Quote:
U-brake
A form of cantilever brake that works like a centerpull caliper. The "L"-shaped arms cross over above the tire, so the left brake shoe is operated by the right side of the transverse cable. A U-brake uses studs that are above the rim, rather than below the it, as with conventional cantilevers. They use the same type and placement of studs as rollercam brakes do.
In 1986-88 there was a fad for equipping mountain bikes with U-brakes mounted underneath the chain stays. This provided a nice clean look to the seat stay area of the bicycle, and provided a somewhat simpler cable routing. In addition, since the chain stays are larger and more rigid than typical seat stays, the "problem" of flexing of the studs under load was reduced. Conventional cantileves cannot be mounted on the chainstays, because the cantilevers would get in the way of the cranks.

Although U-brakes were cool looking and powerful, the fad died quite abruptly when people actually started using the bikes that were sold with chainstay-mounted U-brakes. They had several serious drawbacks:


The inaccessible location made it very difficult to service or adjust the brakes.

They complicated the process of wheel removal.

They tended to get clogged with mud.

Due to the high-mounted studs, if you didn't monitor the brake shoe wear carefully, as they would wear, they would hit higher and higher on the rim. Eventually, they would overshoot the rim and start rubbing on the tire sidewall. This is one of the fastest known ways to destroy a tire.


:wink:


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PostPosted: Fri Nov 24, 2006 10:38 am 
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Thi guy is just a genius .

:lol:


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 Post subject:
PostPosted: Fri Nov 24, 2006 7:25 pm 
Retro Guru

Joined: Fri Apr 28, 2006 8:42 pm
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Location: Brighton
The other reason for popping them under the chainstay is that people used to hang off the back of their bikes for extreme descents - and old style cantilevers on the seatstays could get in the way. People also used to fit Blackburn rear racks as an extra 'saddle' to avoid having the tyre remove their scrotum if they misjudged exactly how far back and low they could go.

I had an XT seat Q/R and a HiteRite so I could quickly dump the saddle down while riding, get back and rest my breastbone on the saddle. When things levelled out, I undid the Q/R and the HiteRite popped the saddle back up again.

The advantage of being so far back, as well as allowing steeper descents to be managed, was that you then had enough weight behind the back wheel to be able to use the rear brake to stop you - reducing the chances of a faceplant. A U-brake gave you enough stopping power to make this work.

*Makes note to self to go and search parts shelf for HiteRite*


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 Post subject:
PostPosted: Sun Nov 26, 2006 8:47 am 
Old School Hero
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My first real mtb was a 1987 Bianchi Forte. I still remember the salesperson telling me the U brake was much stronger on the chain stays than on the seat stays. All the drawbacks Sheldon mentions are true, but there is more. My Bianchi had semi-horizontal rear drop-outs. On severe cranking, the rear tire would pull forward a bit. I would have to stop on occasion and recenter the tire. During my first ever mtb race in 1987, I had to climb a short steep ascent onto a road. At the start of the climb I stood up and cranked. Of course this pulled the tire forward on the drive side. The rear tire moved so far forward that it hit the dia-compe U-brake calibers/arms hard enough for the straddle cable to come off. I must have had the quick release a little loose??? This then allowed the arms to spring back and dig into the tire. The arms stopped the tire cold. Of course, I did not know this as I was just cranking up the climb. It stopped me dead and I fell over. I flipped the bike over on its seat and handlebars thinking I just needed to center the rear wheel. It took me a few minutes to figure out what happened. THen it took me another five minutes to hold the brake arms (there are two) and pull the tire out at the same time.

Thunderchild
www.urmb.org


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 Post subject:
PostPosted: Sun Nov 26, 2006 12:16 pm 
Old School Grand Master
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Location: No brakes? Way to commit soldier.
That sounds more like a fault with the bike than the brake.

The designer of the U-brake probably made the assumption that the rear wheel was held solidly in place. You could say the same with disc brakes, cantilevers or V's they would all be useless if the back wheel moved forward in the drop outs.


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