Brake ratio?

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Jun 6, 2003
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I have a question: on the front of my Egli I have a 4ls which with my bad arm giving me some problem as I can use 2 fingers easyly and the all hand with more difficulties ( like in a panic situation!). I toyed with linking the rear pedal with one side of the brake; change the front fork for a disc one (very narrow Cerriani GP and gas tank very close to the trees + $$); my last idea is to convert the brake lever and cable to the junction box to hydraulic.
I have a spare Magura slave cylinder (clutch) which could fit on top of the junction box/cables to each drum side.
The piston in the slave is 10.5mm and I am thinking of using a master cylinder with a 16mm piston to have about a 1.5 ratio.. Is it too much a ratio? Too much power assistance?
What is a cable/lever/drum normal ratio (or how is it calculated)?
Thanks.
 
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I would have a look at the linked system which is (has been ?) used on Moto Guzzi motorcycles, and talk to a service mechanic about their ratios.
 
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prmurat said:
The piston in the slave is 10.5mm and I am thinking of using a master cylinder with a 16mm piston to have about a 1.5 ratio.. Is it too much a ratio? Too much power assistance?
What is a cable/lever/drum normal ratio (or how is it calculated)?
Thanks.
That ratio would be working against you.You would have to pull 1.5 times as hard (but only move 2/3 the distance).
 
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I've got two AP Lockheed calipers on the front of my Seeley. I use the Lockheed master cylinder normally used for only one caliper and I've got old style asbestos pads in both sides. One finger is enough to do a crash stop. I had a similarly light 7R AJS brake in my old 500cc Triton. Once when one idiot with disc brakes popped in front of me and braked, I grabbed it too hard and the front broke away and went into a lock to lock crashing tank slapper. I was a bit out of practice and didn't get my hands off the bars quick enough and got flicked over the front at about 70 MPH. I still prefer a one finger brake. If care is taken, I find it much better than having to grab a handful really hard. You need to be able to operate the throttle and change gears while braking. Practice makes perfect.
 
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The brake hand lever length to its pivot bolt divided by the distance from the cable end to the pivot bolt is the hand lever’s mechanical advantage (handle movement distance × effort = cable movement distance × pull at the cam lever on the backing plate). The brake lever length at the backing plate from the cable end to the lever pivot divided by the lever length from the lever pivot to the cam is the brake lever’s mechanical advantage. The brake lever multiplies the mechanical advantage of the cable. In general only 2LS and 4LS brakes have this lever type single leading shoe types typically have only a single lever operating the cam directly from the cable. The cam lever length from the pivot to the cam divided by the cam’s eccentric motion (the height of the cam lobe) is the cam’s mechanical advantage.
There is no arrangement or combination of parts that gives lighter hand pressure with the same effort applied to the shoes, or the same hand pressure with stronger shoe application. Every choice of components and sizes is a compromise, whether operated by cable, lever, hydraulic cylinder, or any combination of these. Greatest efficiency will derive from the most rigid parts, reducing all flex and slack, and lubrication. Your time and money would be better spent re-lining your shoes with a modern compound such as 2520V and then having them arced correctly to your drum.
 
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domiracer66 said:
The brake hand lever length to its pivot bolt divided by the distance from the cable end to the pivot bolt is the hand lever’s mechanical advantage (handle movement distance × effort = cable movement distance × pull at the cam lever on the backing plate). The brake lever length at the backing plate from the cable end to the lever pivot divided by the lever length from the lever pivot to the cam is the brake lever’s mechanical advantage. The brake lever multiplies the mechanical advantage of the cable. quote]

Does this mean he would be better off making longer levers to fit the clamp which is then mounted further in on the handlebars :?: :idea:
 
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I modified the lever on the backing plate of my 7R AJS brake by extending it about 1 inch. The brake became 'one finger', and I always like it better that way. However it is much easier to crash yourself if you over react slightly to situations. I used a soft lining and a hard lining on the two brake shoes, so that you had brakes both early and late in a race. It is extremely important that the brake always comes off instantly after you have used it - too much self-servo can cause it to drag. Motorcycle steering geometry is designed to make the bike stable under brakes, If the brake drags you can find yourself running wide in a corner and having a much closer look at any obstacles in the surrounding countryside. I avoid riding bikes with drum brakes, it only takes the leader to heat up and become sticky, and you can find yourself with an injury. I had my worst day at Phillip Island as a kid - my record - 4 times in one day, and one of them was at about 90 MPH. I fell onto the non-skid, and rolled every inch of the way with my bike screeching down the track beside me. If you crash, it is always better to get straight back onto the bike, however in that case it became ridiculous.
With disc brakes there are two words to be remembered - 'rubber lube' - great if you need it.
 
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