Tuesday, November 22, 2011

Bike Shop Horrors: Gutted Part II

Once again I take you inside a bike where you normally wouldn't go. This one is a bit unusual in that it is a part of a "tri-bike", themselves being an unusual breed of bicycle in the first place. (And many times a horror to work on for bike shop mechanics for lots of reasons.)

Down under....
Here we have a view from the bottom side of a Trek Speed Concept rig. Aero/time trial type bikes are bicycles governed by the strange rules of aerodynamics and the UCI. (Which one of those is stranger is another deal altogether.) Since they are governed by these seemingly opposing forces, we get some weird, sometimes inspired designs made to cheat the wind.

In this case, we have a bicycle which has removed the rear brake from its traditional place to underneath the bottom bracket. Gets it out of the air flow alright!

In the image here you see a cover which directs whatever air is flowing around down here by the brake mechanism cleanly. (Never mind that whirling crank set and that spinning rear wheel!)

Kinda like how Charlie would have done it...

Here we have a view with the cover off. Doesn't look like a typical road brake, does it? That's because it has more in common with a mountain bike brake from about 30 years ago than it does any road brake we know from today. And that mountain bike brake is a take off from a design used early in the 20th Century.

The two pivots are easy to find here. If you follow up from there, each brake arm cants inward to the center line of the bike until the arms terminate where you see the two small circular elements at the ends of each arm. These are pins that ride the edges of the triangular shaped "cam" plate you see which has the brake cable emanating from its top, and a bolt near its base above the spring. The bolt anchors the brake cable.

When the brake is activated, the cam plate moves upward, (as we look at the view here), and forces the two arms outward along the cam's profile, which the two pins ride on that are anchored in the ends of the brake arms. The arms pivot, in turn, and like a see-saw, they push the brake pads into the rim as the arms pivot on those silver colored bushings. When the brake lever is released, the spring attaching both arms above the tire pulls the tops of the arms back in, and the brake comes to its resting state as seen here.

It is also notable here that you can see the front derailleur cable on the right, and the rear derailleur cable on the left on either side of the brake cable above the brake itself. All cables are internally routed for better aerodynamics.

This brake is very reminiscent of the 80's "under-the-chain-stay" "Rollercam" style brakes which this looks like a miniaturized version of with a cross spring instead of the two wire linear springs that Rollercams used.

And there is your look at the "guts" of a tri-bike brake.


Fred Blasdel said...

Instead of getting swamped with mud, they get peed on :(

GOB said...

I don't beleive that this is a triathelete's bike, as the brake mechanism appears to be totally free from severe oxidation due to acidic pools of sweat from 4 hour trainer sessions, as well as spray from dripping sugar water sippy cups, and of course, urine.

Matt said...

All of this because putting brakes on your seat stays causes too much wind resistance??

Do these brakes even work well?

Guitar Ted said...

@Matt: They seem to work really well, actually.

Unknown said...

I'm actually impressed with this design. Looks well thought out, especially regard to the derailleur cable routing.

As to the design of the brake itself, it is a straight up roller cam. Set up should be no more difficult.

GranvilleGravel said...

I still have my '85 Cannondale M500. And the rollercam brakes work just fine, thank you. The word on the street in 1985 was that you could dent your rim if you squeezed too hard on the brakes. At least that's what all the kids believed.

Anonymous said...

this specific brake design and chain stays mount was already common in the 70's. before mtb existed.