Rearset/drum brake leverage
- Thread starter AgentX
- Start date
Cool thanks Kris. I think they miss you and your 550 and those cool rearsets. You should drop by and see if you can sell a few sets. At least get in the SERVICES section so people can find you. (or are you there already and I didn't look??) Took the Phat Trakka for a dyno run with different pipes - very interesting.
scm
Been Around the Block
FunJimmy said:
Jimmy, you're still not diggin it.
The lever at the brakedrum remains as before,
the one at the footpeg gets both arms shortened
the same percentage to obtain the old mechanical
advantage.
CCRider perfectly proved that by a little calculation
in his first post. Suggest you go through that, it's
pretty simple.
The basic rule is to keep the ratio of lever lengths
unaltered at each pivot.[1] Your suggestion breaks
that rule as the ratio breakcam:breakarm will be
increased.
Best regards
Sven
[1] to be more precise: keep the product of these ratios unaltered
FunJimmy
Been Around the Block
scm said:
Sven,
Don’t worry, I’m digging it.
A brake system has to be viewed as whole, not just individual components.
If you re-read CCRider’s post, you will see that more rotation is required to pull the same rod length even when retaining the short arm, long arm ratio that the stock pedal has. That means the two do NOT share the same mechanical advantage. The new short pedal will have a greater mechanical advantage over the stock unit at the expense of rod travel. Shortening the drum brake lever brings the complete system back into balance as a shorter drum lever requires less travel to accomplish the same result.
scm
Been Around the Block
Sorry Jimmy, the mechanical advantage equals the short arm, long arm ratio per defintionem.FunJimmy said:
No need to care about rotation or even travel, torque is the dimension to be considered here.
Once again, the mechanical advantage remains the same as it equals the unaltered lever ratio.
Forget about the travel, it's just confusing you, think in terms of force, distance (length of lever)
and torque.
And again: forget the travel! With the same force at the rod (= actuating force on toepeg * lever ratio)
and a shorter drum lever we have less torque at the brake cam, hence less force at the brakeshoes,
hence less deceleration.
Alright?
Best regards
Sven
FunJimmy
Been Around the Block
Sven,
I understand that the principals of a fulcrum, but in this application the fulcrum is only a part of the complete system.
Unfortunately, a mechanical brake system doesn’t have as many variables as hydraulic systems. Hydraulic systems have the same lever ratio issues that our mechanical systems have, but they also have the master cylinder piston bore as another variable. Increasing the piston bore will push more fluid and can be used to adjust the relationship between the pedal assembly and the brake. Mechanical systems don’t have this variable and therefore the relationship between the two systems must be a combined formula.
I understand that the principals of a fulcrum, but in this application the fulcrum is only a part of the complete system.
Unfortunately, a mechanical brake system doesn’t have as many variables as hydraulic systems. Hydraulic systems have the same lever ratio issues that our mechanical systems have, but they also have the master cylinder piston bore as another variable. Increasing the piston bore will push more fluid and can be used to adjust the relationship between the pedal assembly and the brake. Mechanical systems don’t have this variable and therefore the relationship between the two systems must be a combined formula.
CCRider
Coast to Coast
FunJimmy said:
If you'll re-re-read my earlier posts (carefully this time), you'll see that nothing has been done at the expense of brake rod travel. Mechanical advantage, travel of the brake pedal and travel of the brake rod are exactly the same between the two example brakes. Again, who cares about rotation, if the distance your foot has to travel is the same?
CC
DrJ
Over 1,000 Posts
This tread has gotten a bit too sciencey for me. I just know the basics of leverage ratios and what works in the real world. Yes, the mechanical advantage of a lever stays the same if the ratios remain the same but you need to take in practical factors like how long is your foot from heel to toe. A brake lever is useless if it's 3 inches from the toe peg to the footpeg even if it has the same ratio as stock.
AgentX
Over 1,000 Posts
Well, for practicality's sake, I'm going to try it with the stock brake actuator first.
(I'm not gonna engage on the physics of it all but appreciate reading the discussion.)
The Royal Enfield actuator arm will be difficult to shorten and retain full function in the adjuster. There's a built-in pass-through arrangement which allows an adjuster nut at the end of the rod to function. Easier to leave this intact than to cut it off and try to drill the stub of the actuator arm for a clevis attachment, since then I'd need a turnbuckle-style arrangement on the brake connector rod to offer some adjustment.
Although that'll be the thing to do if I end up needing to shorten it.
Shortening from the top end is a no-go because the arm attaches to the mounting stud via tiny splines, so the machining needed to re-drill and fit that back up would be dumb.
-Mike
(I'm not gonna engage on the physics of it all but appreciate reading the discussion.)
The Royal Enfield actuator arm will be difficult to shorten and retain full function in the adjuster. There's a built-in pass-through arrangement which allows an adjuster nut at the end of the rod to function. Easier to leave this intact than to cut it off and try to drill the stub of the actuator arm for a clevis attachment, since then I'd need a turnbuckle-style arrangement on the brake connector rod to offer some adjustment.
Although that'll be the thing to do if I end up needing to shorten it.
Shortening from the top end is a no-go because the arm attaches to the mounting stud via tiny splines, so the machining needed to re-drill and fit that back up would be dumb.
-Mike
AgentX
Over 1,000 Posts
Tarozzis arrived in India today! Sweet. They're nice-looking bits of gear. Can't wait to get them mounted up.
Anyone have experience with these, though? Two questions...I emailed Jim at FastfromthePast but thought I'd ask here, too.
1-Plan is to mount them against flat steel plate. The slight protrusion of the peg shaft past the inboard edge of the shift/brake arm is what's intended to seat against the plate, correct? (ie, leaving a hair's breadth of space for the arm to rotate without it riding directly against the flat mounting surface.)
2-The backing surface of the arm is an alloy disc with two holes in it...these are for a pin spanner (or the like) allowing you to unscrew the backing and re-set the resting position of the arm, right? Anyone know if they're standard or reverse threads?
Edit: Jim responded super-fast. "yes" to #1 and "yes, use a pin spanner and the threads are standard RH" to #2.
Anyone have experience with these, though? Two questions...I emailed Jim at FastfromthePast but thought I'd ask here, too.
1-Plan is to mount them against flat steel plate. The slight protrusion of the peg shaft past the inboard edge of the shift/brake arm is what's intended to seat against the plate, correct? (ie, leaving a hair's breadth of space for the arm to rotate without it riding directly against the flat mounting surface.)
2-The backing surface of the arm is an alloy disc with two holes in it...these are for a pin spanner (or the like) allowing you to unscrew the backing and re-set the resting position of the arm, right? Anyone know if they're standard or reverse threads?
Edit: Jim responded super-fast. "yes" to #1 and "yes, use a pin spanner and the threads are standard RH" to #2.
greasemonkey75
Active Member
I am just chiming in here and this is how I understand it. I will equate it to a ratchet on a nut. If I have a 2' breaker bar I will have to move it a much longer distance than a short.ratchet but with a lot of mechanical advantage. Just like the shorter brake lever on a rear set. However if I increase the drum ARM I will return mechanical advantage, but will have to move short pedal twice as far. Am I getting this. If you are following me. I would recommend a calf workout. Lol
crazypj
Split personality, I fake being smart
You don't want to much rear brake on a cafe, (if you actually intend to ride it instead of 'have the look' for posing)
Front brake will be doing minimum of 75% but often 90%~100%.
On my CB550f, I was getting around 4,000 miles to a set of front brake pads (dual disc conversion)
I changed rears around 50,000 (106,000 miles)
Rear brake is only there to 'steady' bike, not really used for stopping
Front brake will be doing minimum of 75% but often 90%~100%.
On my CB550f, I was getting around 4,000 miles to a set of front brake pads (dual disc conversion)
I changed rears around 50,000 (106,000 miles)
Rear brake is only there to 'steady' bike, not really used for stopping
Front brake has always been the brake of choice for us old farts PJ, but it's not being taught by our licensing authorities nowadays !
It's scary to think there are a bunch of kids hitting our roads that when in trouble are going to hit the back anchor as hard as they can, no wonder 18 to 25 year olds are the largest percentage of single vehicle accident deaths in the motorcycling statistics.
A mate just retired from his bike shop found the exact opposite was happening with pad replacement over the last few years, worn rears needing replacement with the machining marks still present on the front discs, go figure!
Sorry to hijack the thread
It's scary to think there are a bunch of kids hitting our roads that when in trouble are going to hit the back anchor as hard as they can, no wonder 18 to 25 year olds are the largest percentage of single vehicle accident deaths in the motorcycling statistics.
A mate just retired from his bike shop found the exact opposite was happening with pad replacement over the last few years, worn rears needing replacement with the machining marks still present on the front discs, go figure!
Sorry to hijack the thread
That's true. Just grab a big handful of front brake and you will probably fall down. Modern bikes have such powerful brakes that i suspect dealers may be advising newbs to avoid grabbing the front brake and that has been incorrectly internalized as only use the back.
AgentX
Over 1,000 Posts
You don't correct bad technique by advocating worse technique. (Edit: Actually, many people do, hence this discussion...but it ain't right.)
And there are precisely no bikes in the Indian context which qualify as having over-powered brakes. Tiny drums front and rear, mostly, with a smattering of crappy front discs in there. Unless you get into the super-exotic realm, in which case you get what the rest of the world considers a normal modern bike.
And there are precisely no bikes in the Indian context which qualify as having over-powered brakes. Tiny drums front and rear, mostly, with a smattering of crappy front discs in there. Unless you get into the super-exotic realm, in which case you get what the rest of the world considers a normal modern bike.
I took the riding course last spring, here in Illinois. And yes they were ALL ABOUT using the rear brake. only using the front on an absolute emergency only basis. And because thats what they taught us 99% of my brake usage is rear. my old 1980 ATC 110. didnt have a front brake. So using rear comes very natural.