Brake cylinder bores and other braking information

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Founder, Choppers Australia
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Joined: Sat Oct 22, 2005 3:54 pm
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Brake cylinder bores and other braking information

Post by Prof » Mon Feb 27, 2012 11:25 am

Smaller bore size = less effort... it's the difference in diameter between master and caliper that reduces the effort and gives discs an edge over drum in braking effort.

xs650 with single front disc.... master cylinder bore = 18mm, caliper bore = 48mm (these measurements within about 1mm)

standard HD 70's through 80's... master cylinder bore = 16mm, caliper bore = 38mm (1.5")

HD master cylinder bores also available for varoius models in 9/16" (14.43mm) and 11/16" (17.8mm)

Something to also keep in mind is the leverage at your hand lever. I rode a Honda recently with short flat bars. The master cylinder was flat against the throttle group meaning my hand gripped the brake lever half way in. Gripping the lever out near the outer end almost doubled the leverage and the brakes felt much more powerful.

Also bear in mind that early HD brake ratios were set up to be fairly hard, to minimise skidding in panic situations.

Also bear in mind the big difference in braking effort required with soft versus hard brake pads and also between iron versus stainless rotors.

Chopper braking is a bit different to sports bikes. Extending front forks, lengthening the bike, sitting back and upright all move more braking to the rear wheel. Lightening the bike (one prime motivation with chopping) also improves braking overall and sitting upright and cruising tends to increase the braking time available.

Rear disc brake setups are not so difficult as you can vary the leverage at your brake pedal.
Chopit'nrideit... Prof

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