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Location of rear brakes and impact on braking

Road Cycling “It is by riding a bicycle that you learn the contours of a country best, since you have to sweat up the hills and coast down them. Thus you remember them as they actually are, while in a motor car only a high hill impresses you, and you have no such accurate remembrance of country you have driven through as you gain by riding a bicycle.” -- Ernest Hemingway

Location of rear brakes and impact on braking

Old 01-03-13, 06:51 PM
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thehammerdog
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Location of rear brakes and impact on braking

I was just reading up on the new BMC grandfondo comfort bike the stays are set very low down on frame, some others have brakes under BB while most are "normal"....does the location make a difference in power or effectiveness....just wondering.
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Old 01-03-13, 08:17 PM
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No, they all have the same length lever(ie the wheel braking surface) to use for braking power. Time trial bikes have them under the chain stays for aero reasons and such.
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Old 01-04-13, 07:53 AM
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I was wondering if location from high to low center of gravity of bike weight location and stiffness of said location results in any changes pro/con....seems like a decent research project for someone....they now find rim size width makes a difference
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Old 01-04-13, 08:10 AM
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Moving a 200g brake caliper is not going to make a noticeable change in the CG of the bike+rider. Even if it did it would not change anything related to performance.
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Old 01-04-13, 08:26 AM
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Caliper placement doesn't affect rotational torque. Rotation depends on suspension design. If you don't have suspension then you really don't have rotational torque, at least not in a specific direction.

Caliper placement technically affects center of gravity but caliper weight is so minor compared to, say, the rider, that it really doesn't make a difference. When a rider is out of the saddle the bike basically rocks back and forth around the bottom bracket. (I understand that the bike has to tilt at the tires, but a rider properly riding out of the saddle will make a small swerving path which allows the tires to wiggle back and forth under the basically-straight-line-travel-BB). I suppose that if the calipers were mounted at hub level there'd be less caliper-induced inertia, but, again, it's very minor.

Most riders, on the other hand, will be able to tell a 200g difference in saddle weight when out of the saddle. The saddle is very high, usually the furthest from the BB compared to any other weight on the bike itself, and it moves the most when a rider is out of the saddle. As an experiment you can strap a water bottle to your saddle rails and see what your bike feels like out of the saddle with the bottle full or empty.

I recall that front caliper placement affects aerodynamics the most. The rear is less significant due to all the stuff in front of the rear brake. Again, though, the net effect is very minor at mortal speeds.

The short answer? It really doesn't matter.
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Old 01-04-13, 08:49 AM
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you mean rear brakes don't always go under the chainstays?

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Old 01-04-13, 11:02 AM
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Originally Posted by thehammerdog View Post
I was wondering if location from high to low center of gravity of bike weight location and stiffness of said location results in any changes pro/con....seems like a decent research project for someone....they now find rim size width makes a difference
But for any given rim size, the location of the caliper along that circumference makes no difference, because as drelyt pointed out, the length of the lever is always consistent: The distance from the axle to the rim is the same regardless of where along that rim you choose to locate it.
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Old 01-04-13, 11:13 AM
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IMO, it's basically a bad idea. All else equal, it doesn't make a difference in braking, but hanging below the BB with the brake pads perpendicular to the wind may be out of sight but not out of the wind. I'm not sure it's any more aero, though some appear more "tucked in" than others. They're harder to inspect, adjust and work on. The cable is longer. They're going to be subject to spray, grit and carp (sic) thrown up by the front wheel, but less subject to stuff carried around by the rear wheel...maybe a wash, so to speak.

Trek makes the argument that the seat stays can be thinner because they don't need to handle braking loads and are thereby more compliant. Perhaps, a little, but probably no more compliant than can be achieved by other means.

The good news is it's only the rear brake.
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