Cycle Forums: Motorcycle and Sportbikes Forum banner
1 - 9 of 9 Posts

·
Registered
Joined
·
781 Posts

·
Registered
Joined
·
1,248 Posts
Discussion Starter · #4 ·
ok, pardon me if this sounds completely stupid but lets say i were rtying not to spend $500. I am going to put it on my sv, basically a gixxer 750 front end. Now..

the yoyodyne site with the rear master that is linked above, use that one to replace my existing one. Instead of buying the thumb brake on there, the master that is with the lever. Isn't a 13mm brembo clutch master the same thing in essence just a little bigger? So if i made a bracket for it and got a smaller lever, would that work? anyone know? or am i hopelessly trying to fabricate something that won't work?

Thanks!!!
 

·
Registered
Joined
·
781 Posts
If I understand it all correctly, the Brembo (Yoyo link) one I posted is a "Flow Through" design which allows you to use both the rear pedal, and a second master on the bars. If you want to do away with the foot pedal altogether, you could just install a master on the bars and a long line. That'd save you the trouble/expense of the Brembo flow through master I posted.


Now, as far as M/C size, you have to be careful: What you put in at the top gets multiplied at the bottom in an inverse fashion. Meaning the Difference in area is what counts as far as outright power. Sounds backwards, but a smaller master actually generates more outright power than a larger one. I've done the math on this site before, but will skip it and simply say that the 10 lbs your hand may put on the lever can generate 2500 pounds on the rotor...


So I would recommend chatting with someone at Brembo, or one of the sites who have done this mod and get their recommendation. Up front, more power is generally better, but it's easy to lock up a rear. Better to have something you can modulate accurately.

As far as money - Keep an eye on the classifieds at http://www.roadracingworld.com or the WERA boards, or NESBA, or whoever handles trackdays in your area. Ask there who has done this and how they best recommend going about it. You could get lucky and pick up someone else's used one. But I feel I should state that Brakes are something I don't screw with, and that if it were me I'd either buy new or scrap the idea altogether.

Good Luck!!

Scott :)
 

·
Registered
Joined
·
1,248 Posts
Discussion Starter · #6 ·
i'll keep my eye open for one used, but for brand new its just too expensive for me. I rarely use my foot, and just heard of the thumb brake. I have an idea now how it works, but i am actually interested in the math you said with the pressure involved with the smaller master bore. I would stil use a flow through on the bottom because on off track expeditions i will use it, but not while braking. Thanks though, and look forward to your reply
 

·
Registered
Joined
·
781 Posts
OOPS!!! Looked for it, but it was on another forum...

Cut/Pasted for your reading pleasure...

Yes, a larger master moves more fluid... But a smaller master attains much higher peak pressures because you are applying the same hand pressure onto a much smaller area. That means More Power, but (obviously) to move the same amount of fluid you need a longer stroke. That is why M/C brake pads/pistons are designed to use as little travel as possible.

Now, the cool thing about hydraulics is that ALL PRESSURES APPLY EQUALLY IN ALL DIRECTIONS, ALWAYS. The system is either pressurized, or it is not.

So how it all works is that the force applied by your hands gets multiplied, first by simple leverage of the lever on the master, but then hugely multiplied by the relative surface areas (master:calipers). For example, if the diameter of the slaves is twice that of the master, then that multiplication factor is roughly 4:1. Oh Yeah, I am greatly simplifying the math, so you engineers can please not bother to correct me....


Now, our brakes would have that 14mm piston pushing something like four 40mm pistons on the caliper end. An area of (about) 44mm pushing on (about 125, x 4) 500 sq mm. 11 times the surface area...

So, if you applied 10 lbs of pressure, 5 inches out on the lever (50 in/lbs), through the above setup, the pressure at the caliper's pistons would be (50 x 11) 550 lbs, per square in. Which in turn is multiplied by the surface area of the pads. If we call the pad's surface area 1.5" x 3", that's 4.5 square inches, or 2,475 pounds worth of pressure on the brake rotor.

This, of course assumes no flex, no expansion in the brake lines, and no friction in the system and perfect contact between all working surfaces.

Take a 16mm master cylinder (50 sq mm) through the same process, and you get (50 x 10 x 4.5) 2,250 lbs sq/in. A decrease of 225 lbs worth of pressure for a 2mm increase in master cylinder size.

The issue with a smaller master, is that at some point the lever travel necessary to build pressure becomes excessive. That defines the practical lower limit. Conversely, a larger master feels more immediate, since it moves more fluid and builds to it's (lower) peak pressure sooner. But losses at the master also get multiplied down to the rotors....


That was why there was the push for 6 piston brake calipers for a while. It was an easy way to get a lot of force multiplication. The problem with that was that a lot of the force was lost through flex. So we went back to beefier and less flex prone 4 piston calipers, pushed by smaller master cylinders.

The other things we learn is that a couple mm worth of difference at the master means a BIG difference at the rotor/wheel. So we should take it easy when we start d*cking around with modifications. And if you were really paying attention, you would have figured out that it's a good idea to move your brake lever as far inboard as you can, so you'll grasp it further out and get a little 'free' power from your brakes.

After all, if you grabbed the first example's lever an inch further out (60 in/lbs applied) then your brake rotor gets 2,970 pounds of pressure....


Now that I've bastardized it all to hell and back, if anyone wants to really know the technical detailia behind all this stuff and don't mind Math for Engineers, then pick up a copy of "Motorcycle Tuning - Chassis" by a gentleman named John Robinson.


Does that help??


Scott :)
 

·
Registered
Joined
·
1,248 Posts
Discussion Starter · #8 ·
yeah it does, thanks for posting that. The reason i asked earlier though is that brembo makes a master that is 13mm, but i beleive has a shorter pull than most brake levers. Sort of like a rear pedal would. But now i'm curious as to think that if you had a regular brake master and cut the lever short and applied that, the bigger master would cause less force and therefore not lock up the rear wheel. Brembo and the one on the gp tech website advertise if you ask one of their people that those masters will not lock up the rear wheel. Also i wonder if you ran like a dot 3 fluid if that would help apply a little less force than something like a dot 4 or 5.1 atleast this is turning out to be a helpful thread :)
 

·
Registered
Joined
·
781 Posts
Fluid won't make any difference in power or feel. Just in heat resistance. 3 = med, 4 = high, 5.1 = highest. Don't use 5.0 because it's silicone based instead of glycol. To weaken a too-strong system, some folks have intentionally introduced air into it tho...

As far as locking the rear, I should think that you thumb is a lot weaker than your whole foot. And a lot more sensitive as far as feel/pressure, so I don't think locking would be much trouble once you've developed the touch for the system.

Seriously - Send an eMail or call the folks who make the system. ANd/or post up on a more race oriented site (WERA, NESBA, etc) for someone that's done the mod. They'll know!

Scott :)
 
1 - 9 of 9 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top