Future caliper swap

[robtharalson]

I was changing my front pads (HONDA PADS ONLY!) yesterday, and decided to partially remove the calipers to clean the pistons. While they were off, I trial fitted a pair of gold 929 calipers with new OEM pads in absolutely perfect condition I purchased on EBAY a while back for (hold on to your hats) $32.00 including shipping! They bolted right on -- perfectly centered, pad engagement right where it needed to be, and hoses lined up. The only problem is the master cylinder needs to be 16mm instead of the stock 14mm. Fortunately, I have several 16mm masters to choose from, including a remote reservoir unit, so the next time the pads need replacement, I think I'll install the calipers, master, and braided lines which I also have in bench stock. Believe it or not, it will end up costing less than new pads! Gotta love EBAY.

Thought you would like to know these will fit.

Rob

[PHOBMAN]

I understood that the 919 used the 929's brakes!

[justintyme73]

Originally Posted by PHOBMAN

I understood that the 919 used the 929's brakes!

So how do they stop the 929's if the 919's are using thier brakes??

[robtharalson]

The 929 calipers have larger pistons (32/30 instead of 30/27) and about 20% more pad area. Add that to larger rotors and you have more powerful brakes.
Thank Honda for economizing by specifying calipers with the same mounting centers and "G" distance regardless of internal configuration from Nissin. It makes their, and Nissin's, job much easier.

Rob

[Bryce919er]

Why do you *need* the 16?

A smaller master piston should give more braking than a larger master piston given = input lever force & caliper piston.

A larger caliper piston should give more braking than a smaller caliper piston given = input lever force & master cylinder piston.

So should not the smaller master of the 919 & larger caliper of the 929 be the best? Just a little force(lever)/area(mc piston) at the master that puts a pressure in the line that is the same all the way down to the caliper where it is force(to disc)/area(caliper piston) again.

[gpzTurbo]

ebay rocks. I got the whole front end from an 04 kaw 636 for peanuts.

[xrmikey]

Originally Posted by Bryce919er

Why do you *need* the 16?

A smaller master piston should give more braking than a larger master piston given = input lever force & caliper piston.

A larger caliper piston should give more braking than a smaller caliper piston given = input lever force & master cylinder piston.

So should not the smaller master of the 919 & larger caliper of the 929 be the best? Just a little force(lever)/area(mc piston) at the master that puts a pressure in the line that is the same all the way down to the caliper where it is force(to disc)/area(caliper piston) again.

Volume.
A smaller master will give more pressure but won't move enough volume.
You will run out of lever faster.
Big pucks need big volume.

[robtharalson]

Originally Posted by Bryce919er

Why do you *need* the 16?

A smaller master piston should give more braking than a larger master piston given = input lever force & caliper piston.

A larger caliper piston should give more braking than a smaller caliper piston given = input lever force & master cylinder piston.

So should not the smaller master of the 919 & larger caliper of the 929 be the best? Just a little force(lever)/area(mc piston) at the master that puts a pressure in the line that is the same all the way down to the caliper where it is force(to disc)/area(caliper piston) again.

That's what I thought the first time I did a brake update. T'aint necessarily so! After studying the hydraulic leverage ratios on literally hundreds of motorcycles, I have come up with general guidelines for sizing. First, some background: the force applied to the brake pads is a function of the area of the master cylinder piston to the total area of all the caliper pistons added together. In the case of the 919, the 14 mm master has an area of 1.54 square centimeters, and the caliper pistons 51.176 sq. cm., making a leverage ratio of 33.25:1. This is very close to the maximum ratio experimentation has demonstrated will provide controllable brakes: much above 36:1 tends to get very grabby, especially under panic stops. Additionally, the force required at the lever gets so light, fine control takes a safecracker's touch. The 929 calipers will up the ratio to just under 40:1 with the stock master: far too high for proper control. This drops to 30:1 with a 16mm master.
Interestingly, when the first Lockheed magnesium calipers were introduced to racing, and shortly thereafter the street in the early '70s, the optimum ratio for the organic pad compounds in use at the time was in the 15:1 to 20:1 range. Semi metallic sintered compounds tend to have less "give" than previous organics, and are made harder which requires higher pressures.

The formula for calculating the ratio (in longhand) is:
((LP/2)^2 * PI * NLP + (SP/2)^2 * PI * NSP) / (MP/2)^2 * PI
Where LP = Dia. of the larger caliper piston
SP = Dia. of the smaller caliper piston
NLP = Number of large pistons
NSP = Number of small pistons
MP = Master cyl piston diameter
Pretty cumbersome.
If you are converting to a different multi piston caliper, you will be bucks ahead by following the factory's choice for master cylinder size. In the event of a change such as using only one multi piston caliper for a supermono, calculate a ratio in the 28:1 to 32:1 range and you will not be far off from right.

Whew!

Rob

[Bryce919er]

Thanks for splaining guys. I figured both those issues would show up sometime but did not know if it was here & now.

[robtharalson]

My graphing calculator makes me lazy -- I can enter the most complicated formula or equation and it will run it. For those of you who are challenged on the calculator front, here is a simplified way to determine the ratio using a basic four banger calculator with memory and square root keys:
(LP^2 + SP^2) * (either NLP or NSP, but not both) divided by MP^2
Or for directly calculating master cylinder size, take the square root of this:
((LP^2 + SP^2) * NLP) / The ratio you think you want)
LP = Dia. of the larger caliper piston
SP = Dia. of the smaller caliper piston
NLP = Number of large pistons
NSP = Number of small pistons
MP = Master cyl piston diameter

There now, that wasn't so bad was it?

Rob

[Bryce919er]

What about HP's?

[robtharalson]

Hell, an abacus will work if you have a clue how to do it, so if you are used to RPN, the HP will do fine. I hauled out my ancient slide rule and got a pretty accurate answer in about 2 minutes. Whatever floats your boat.

TI 86s rule!

Rob

[mdtoney]

Originally Posted by robtharalson

I trial fitted a pair of gold 929 calipers with new OEM pads. They bolted right on -- perfectly centered, pad engagement right where it needed to be, and hoses lined up. The only problem is the master cylinder needs to be 16mm instead of the stock 14mm. Fortunately, I have several 16mm masters to choose from, including a remote reservoir unit.
Rob

Rob,
Is the 929 master 16mm? I'm assuming it should be since it would be the correct part for the 929 calipers. I have some leftover 929 brake parts that I've been considering for my front-end project, and was debating whether I could keep the 919 master, or whether I should use the complete 929 brake system. From reading this post it now appears that the 919 master wouldn't be the smart choice if I'm using 929 calipers. Just want to make sure.
Thanks,
Mike

[Lemonhead]

Silly request, Rob.

Could you lose the "t" in the middle and leave the gap?

I keep saying "robot haralson".

Thanks

[robtharalson]

Originally Posted by mdtoney

Rob,
Is the 929 master 16mm? I'm assuming it should be since it would be the correct part for the 929 calipers. From reading this post it now appears that the 919 master wouldn't be the smart choice if I'm using 929 calipers. Just want to make sure.
Thanks,
Mike

I'll be checking with the local Honda dealer tomorrow after my PT, so should have an answer then. I don't remember if it's a 16mm (30:1), 17mm (26.6:1)or 18mm (23.75:1). I'll get back to you on that.

Originally Posted by Lemonhead

Silly request, Rob.
Could you lose the "t" in the middle and leave the gap?
I keep saying "robot haralson".
Thanks

Actually, I kind of like the machine reference, and am looking forward to being a cyborg some day, though I'm not holding my breath (while I still have breath to hold). Do cyborgs breathe? I guess it depends on which mad scientist cobbles me together.

Rob (for now)

[robtharalson]

Originally Posted by mdtoney

Rob,
Is the 929 master 16mm? I'm assuming it should be since it would be the correct part for the 929 calipers. I have some leftover 929 brake parts that I've been considering for my front-end project, and was debating whether I could keep the 919 master, or whether I should use the complete 929 brake system. Mike

Well, I went to Kolbe Honda today and got a bit of a surprise -- the 929 calipers, at least the '01, have 34/30 pistons and a 19mm master, making a ratio just under 23:1. They must use relatively soft pads. The ratio with the 14mm 919 master would be 42:1, which would probably put you on your head if a dragonfly hit the brake lever at 75 MPH! This also makes me wonder what Honda my calipers came from. Possibly a CBR 900. There's something to be careful of when buying on EBAY -- the part(s) you get may not be what the seller says they are.
If you are considering a swap with 929 calipers, be sure to trial fit them before commiting to the swap, though I would be surprised if they didn't fit.

Rob

[mdtoney]

Now that I think about it, mine were off a 954 - not sure that would make a lot of difference though. Regardless, I decided to stay with one complete system: the calipers and pads are 954, as is the master and lever so I should be ok.

[soofle616]

Dragging out an old thread with a potentially stupid question.. If using 929/954 calipers, are the stock rotors still used or do the new calipers sit farther out allowing for larger rotors? I can definitely see how more pad area and bigger pistons would lead to better braking, but considering I've managed to warp both my stock rotors with the stock pads and calipers (trackdays) it seems like a caliper swap without bigger rotors would lead to the same issue but faster due to the additional heat generated by the more powerful caliper/pad combo.