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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
front brake upgrades
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<blockquote data-quote="Tom Gaynor" data-source="post: 14693" data-attributes="member: 4034"><p>"Sponge" is in direct relationship to mechanical advantage. The greater the MA (leverage) the greater the sponge. If the shoes have to move 10 thou to go from first kiss to full on, and the MA is 100:1, the lever has to move an inch. Reduce the MA, the "sponge" decreases. But now one has to squeeze a bloody sight harder to get the same braking force. Might even feel "wooden". Go figure what a standard Vincent MA is...</p><p>I had a race bike with a single disc, Lockheed caliper and master cylinder. It stopped, but took so much effort that after five laps I had a forearm like Popeye's. The solution was to change to a Marzocchi master cylinder probably intended for twin discs, and therefore with more MA. (OK, really HA, hydraulic advantage) Sponge increased noticeably - but I could now nail it with two fingers and retain forearms like a ballet-dancer's. Sylph-like? Damn right...</p><p>This isn't to say that one shouldn't eliminate all the slack one can, but ultimately there's a trade off.</p><p>For comparison / callibration, my PV 2ls brakes have something like 1/2" - 3/4" of "sponge" as defined above, with a Magura twin-pull lever (no balance bar), and they stop like a bitch, with two fingers. My 9" (210 mm) Menani four-shoe race brake is about the same in terms of sponge, and in terms of stopping, as good as the single disc was, if not exactly as predictable. (It heats up and the drum expands: the extra shoe travel, multiplied by MA, shows up as sponge, and has to be compensated for. When the lever hits the bar, sunshine, you're intercoursed, or into previously unexplored levels of corner entry speed. ) But that's racing: for road use, unless you plan frequent crash stops from 100+ mph, it wouldn't matter.</p></blockquote><p></p>
[QUOTE="Tom Gaynor, post: 14693, member: 4034"] "Sponge" is in direct relationship to mechanical advantage. The greater the MA (leverage) the greater the sponge. If the shoes have to move 10 thou to go from first kiss to full on, and the MA is 100:1, the lever has to move an inch. Reduce the MA, the "sponge" decreases. But now one has to squeeze a bloody sight harder to get the same braking force. Might even feel "wooden". Go figure what a standard Vincent MA is... I had a race bike with a single disc, Lockheed caliper and master cylinder. It stopped, but took so much effort that after five laps I had a forearm like Popeye's. The solution was to change to a Marzocchi master cylinder probably intended for twin discs, and therefore with more MA. (OK, really HA, hydraulic advantage) Sponge increased noticeably - but I could now nail it with two fingers and retain forearms like a ballet-dancer's. Sylph-like? Damn right... This isn't to say that one shouldn't eliminate all the slack one can, but ultimately there's a trade off. For comparison / callibration, my PV 2ls brakes have something like 1/2" - 3/4" of "sponge" as defined above, with a Magura twin-pull lever (no balance bar), and they stop like a bitch, with two fingers. My 9" (210 mm) Menani four-shoe race brake is about the same in terms of sponge, and in terms of stopping, as good as the single disc was, if not exactly as predictable. (It heats up and the drum expands: the extra shoe travel, multiplied by MA, shows up as sponge, and has to be compensated for. When the lever hits the bar, sunshine, you're intercoursed, or into previously unexplored levels of corner entry speed. ) But that's racing: for road use, unless you plan frequent crash stops from 100+ mph, it wouldn't matter. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
front brake upgrades
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