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What Size Brembo Master Cylinder?

SEBSPEED

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SEBSPEED Grand Master

SEBSPEED

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I may have a deal on a used Brembo master cylinder - if it's the right size...

Stock 86 VFR master cylinder is stamped 5/8", which translates to 15.87 or roughly 16mm.

I am using CBR600F3 calipers on the bike, but they appear to be about the same as the VFR parts(I know, appearances can be deceiving...)

The Brembo unit I can get is 16x18, will this work for me? There might be another available in 19x20, but that seems way out of line with the stock parts?

Thanks!

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SEBSPEED Grand Master

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I am asking about the bore size of the m/c in relation to the stock setup, but if someone wants to read more on these parts, here's an bit from oppracing.com:

Example: 19x16 Billet Non-Folding Radial Brake Master Cylinder

19x16: This specification indicates two values. The first value is the diameter (ie. bore) of the cylinder in millimeters - it is usually 16mm or 19mm. In this case, the diameter is 19mm. The second value is the inter-axis (ie. distance) between the lever's pivot point and the plunger that pushes into the cylinder - it is usually 16mm, 18mm or 20mm. In this case, it's 16mm.

Now that we know what the numbers are, let's figure out what they mean in terms of braking performance. When you are selecting a master, you need to understand that these values trade-off braking sensitivity and braking power.

For the cylinder diameter, as that value increases, you increase your braking power. As you increase the diameter, you increase your cylinder size and increase the volume of brake fluid that you have to compress. This creates a dampening effect that allows you to better modulate the amount of brake pressure. As a general rule of thumb, you would use a 16xXX for a single caliper set-up anda 19xXX for a dual caliper set-up. Of course, there are always exceptions - for example, the stock master cylinder for Yamaha R1's and R6's (which are made by Brembo) use a 16xXX set-up, despite the fact that they have dual front calipers.

For the inter-axis value, as that value increases (ie. the distance gets longer), you are decreasing your sensitivity and increasing your brake power. I don't want to get into the technical aspect or into the physics of it...that's not the goal of this article. If you feel like you need to know more, I would recommend you search Google or How Stuff Works. In a general comparison between a 19x18 and 19x20 configuration (the most common configurations for sportbikes), a 19x18 has more feel but has a little more lever travel than the 19x20. A 19x20 configuration has more braking power and requires less distance to completely pull in the lever.

Ultimately, the optimal configuration is up to you. Brembo recommends the 19x18 configuration for racers and the 19x20 configuration for street riders. In terms of real world examples, the billet master cylinder using in MotoGP is a 19x18 while the master cylinder includes with the Brembo High Performance street kits is a 19x20.

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V4 Rosso Mentor

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CBR600F3 calipers are about the same as VFR750FL (3rd gen) and later models RC36 with close to 1" caliper pistons and 0.5" master cilinders. The 1st and 2nd gen VFR has close to 1.19" caliper pistons and, like you mentioned, 0.62" master cilinder, big difference. If I had to choose between those two brembo master cilinders I would take the 16x18.

That bit from oppracing is not correct.

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Veefer800Canuck Grand Master

Veefer800Canuck

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Seems like as the pivot point moves further from the master cylinder, the LESS braking force you would have for a given lever pressure.

Think of moving the fulcrum under a fixed length lever further away from the load end. More effort is then required to move said load.

The OPP racing blurb states the opposite

For the inter-axis value, as that value increases (ie. the distance gets longer), you are decreasing your sensitivity and increasing your brake power.

But I think your biggest concern would be the diameter of the master cylinder.

Try to find out the I.D. of a stock CBR F3 brake master cylinder and compare.

16mm M/C = 5.039 eigths of an inch. Close enough if you ask me. (ASS-umung the CBR part is also 5/8" like the VFR's)

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SEBSPEED Grand Master

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Seems like as the pivot point moves further from the master cylinder, the LESS braking force you would have for a given lever pressure.

Think of moving the fulcrum under a fixed length lever further away from the load end. More effort is then required to move said load.

The OPP racing blurb states the opposite

For the inter-axis value, as that value increases (ie. the distance gets longer), you are decreasing your sensitivity and increasing your brake power.

But I think your biggest concern would be the diameter of the master cylinder.

Try to find out the I.D. of a stock CBR F3 brake master cylinder and compare.

Will do Rob. Unfortunately, the CBR boards are not as responsive as this great place... :dry:

Another thought regarding the OPP reference. The way I understood what they wrote, is that the fulcrum point is fixed(pivot point). Now let's say you apply 1mm of brake pressure on the lever. The piston that's 18mm from the pivot point will not move as much fluid as the piston that is 20mm from the pivot point, due to the angle included in the design of the lever(which is also adjustable).

Does that sound right?

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SEBSPEED Grand Master

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16mm M/C = 5.039 eigths of an inch. Close enough if you ask me. (ASS-umung the CBR part is also 5/8" like the VFR's)

Right. Now how would the braking be affected if I used the 16mm m/c with calipers meant to be moved by a 1/2" unit? Brute force? Soft noodles? Or some lesser effect in either direction?

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The 16x18 is for single caliper motards. I would get the 19x18. I have the 19x20 on my gsxr (four piston calipers) and it is a bit firm. The nice thing about the radial is you can adjust the take up point quite a bit. Most racers that I know use the 19x18 as it give more feel and many of them have the remote adjuster knob to make adjustments on the fly. With the smaller volume of the old calipers I think the 19x18 would work great.

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I am using CBR600F3 calipers on the bike, but they appear to be about the same as the VFR parts(I know, appearances can be deceiving...)

They are the same as 4th gen as far as bolt spacing and pads. I don't know why the 4th gen and the F3 have different pad PN's but they have exactly the same backplates.

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Thanks very much! Have you tried a 19x20? /have any input on that size for this application?

I have thought about throwing the brembo on my V7 bike but I've never gotten around to it. The oem one works and I don't feel like rebleeding just to see if it would work. Actually, I'm afraid that it would cost me more money if I felt how good it could feel... Although, I think it would be to touchy with the 19x20 since the F3 and 05 gsxr pistons are similar in size and the gsxr has twice the amount.

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SEBSPEED Grand Master

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Thanks very much! Have you tried a 19x20? /have any input on that size for this application?

I have thought about throwing the brembo on my V7 bike but I've never gotten around to it. The oem one works and I don't feel like rebleeding just to see if it would work. Actually, I'm afraid that it would cost me more money if I felt how good it could feel... Although, I think it would be to touchy with the 19x20 since the F3 and 05 gsxr pistons are similar in size and the gsxr has twice the amount.

Sorry - which would be too touchy w/ the 19x20? The F3 or the GSXR? Or both? You're saying the GSXR has a larger swept area o nthe rotor due to bigger pads and then would be too touchy?

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Sorry - which would be too touchy w/ the 19x20? The F3 or the GSXR? Or both? You're saying the GSXR has a larger swept area o nthe rotor due to bigger pads and then would be too touchy?

I think the F3 would be touchy with the 19x20. I like it on the GSXR but the gsxr has double the amount of pistons as the F3. The diameter of the piston in a radial master cylinder (19mm) does not correlate to a standard master cylinder piston size. The second number (18 or 20mm) is a measurement of the distance from the pivot point at the inside of the lever to where the lever connects to the piston in the middle of the lever. The lower number offers more mechanical advantage and more lever movement to achieve a given brake pressure (ie more feel)

What are you going to use for a brake light?

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Veefer800Canuck Grand Master

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16mm M/C = 5.039 eigths of an inch. Close enough if you ask me. (ASS-umung the CBR part is also 5/8" like the VFR's)

Right. Now how would the braking be affected if I used the 16mm m/c with calipers meant to be moved by a 1/2" unit? Brute force? Soft noodles? Or some lesser effect in either direction?

Using a larger master cylinder in a given application will result in the need to apply more force to the lever to obtain (x) amount of braking force, and therefore, deceleration.

Yes, you are moving more fluid per unit of stroke, but you are decreasing your mechanical advantage over the slave piston(s).

Example: Safe-T installed a Duc rear caliper on his Viffer and stayed with the stock VFR 17mm rear master. Duc caliper = itty bitty single piston jobbie, Vs VFR's four (footpedal only) pistons with larger area than the Duc unit.

Now going smaller on the slave cylinder is the same effect as going larger on the master cyl, all else being equal.

The result was a rear brake that you had to have an 800 Lb gorilla stand on to get any braking at all. I about sailed into the first intersection I came through as I usually taper off the front brake and transition to rear brake only (at very low speed) for a casual, routine street-legal stop. Didn't work, Aieeeee!

Example #2: My brake delinking after the USD fork swap. 17mm VFR master working all 3 pistons out back instead of (normally) working two out back and 2 in front. Basically I lost one piston out of the equation, for less (slave) surface area overall.

Therefore, smaller area at slave = same effect as greater area on master, all else being =

My brakes were 100% bled out, and were completely wooden, no power, couldn't lock the rear even on purpose. To compensate for smaller rear piston area, I had to DECREASE the master cyl from 17mm to 14mm. Now, I have great rear brakes and can lock the rear wheel with reasonable effort. And yes, they were both bled out perfectly.

Which shows that:

Using a smaller master cylinder in a given application will result in the need to apply less force to the lever to obtain (x) amount of braking force, and therefore, deceleration.

The only drawback to option #2 is that you will need a longer stroke to do the same amount of work in.

Stick as closely as possible to the OEM standard for M/cyl bore.

That was the long answer. The short answer is that using a 16mm master in place of a 12.5mm master will result in awfully wooden feeling brakes with far less power, unless your (new) brake lever is exceptionally long, or the pivot point is appreciably closer to the actual piston, giving you more mechanical advantage at the lever/fulcrum to make up for the loss of hydraulic advantage.

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Veefer800Canuck Grand Master

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Swiped off the Intardweeb:

Hydraulic Ratios

Before buying a new Master Cylinder from Performance Machine and plumbing it to the stock factory Caliper from that 1996 Sportster you have to consider the hydraulic ratio between the two components.

To explain hydraulic ratios we have to re-visit high school physics. It all comes down to one formula: Pressure = Force/Area. So if you put ten pounds of force on a master cylinder piston with one square inch of area, you have created a pressure of 10psi. If you change the master cylinder to a design with only 1/2 square inch of piston area, then you've created twice the pressure. The important part isn't just the 10psi of pressure, it's how that 10psi of pressure is utilized by the caliper.

If the caliper in question uses one piston with one square inch of piston area the force on the brake pad will be 10 pounds (Force = Pressure X Area). If you double the piston area you also double the force on the brake pad. After only a moment's consideration you realize that the way to achieve maximum braking force is with a small master cylinder piston working multiple caliper pistons with relatively high total area.

Remember though that everything has a price (no free lunch, ever). Small master cylinder pistons don't displace much liquid, and may not fully extend the caliper pistons. Matching up the best components is a matter of balance then, between pressure and volume.

If you're buying a complete new set up for the front wheel of that chopper, ask the sales person to recommend which master cylinder (they come with various piston sizes) to use with that four-piston caliper. If instead, you're mating a new master cylinder to an existing caliper, buy one with the same diameter piston as that used on the donor bike.

The bigger the master cylinder piston the more fluid is displaced. As the piston size grows however the amount of pressure (all other things being equal) goes down. Output is also affected by the lever ratio, which is why some metric masters have adjustable pivots.

The force created in the master cylinder is transferred fully to the caliper pistons. The more piston area the more net force is created by a certain pressure. The trade off: more pistons (or calipers) require more volume to move all those pistons. That's why the diameter of the master cylinder piston is so important.

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Stick as closely as possible to the OEM standard for M/cyl bore.

Radial master cylinder size numbers do not correlate to at all to the dimentions given for a standard type master cylinder. Using the size of a standard to pick the size of a radial is comparing apples to oranges.

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V4 Rosso Mentor

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That bit from oppracing is not correct.

Can you elaborate on that? I'd like to remove it before I spread bad information... :unsure:

Well, they got it all backwards:

For the master cylinder diameter, as that value increases, you increase your braking power. As you increase the diameter, you increase your cylinder size and increase the volume of brake fluid that you have to compress. This creates a dampening effect that allows you to better modulate the amount of brake pressure.

It is just the opposite: smaller diameter make it possible to get higher brake line pressure, all else equal resulting in higher brake force.

Also the claim of the dampening effect due to increase of brake fluid volume is BS as the volume increase is maybe 1% or even nill as it is dictated by the size of the caliper pistons (larger master cilinder bore means less travel).

For the inter-axis value, as that value increases (ie. the distance gets longer), you are decreasing your sensitivity and increasing your brake power.

If the inter-axis value :unsure: pivot length increases you are decreasing your brake force.

Ultimately, the optimal configuration is up to you. Brembo recommends the 19x18 configuration for racers and the 19x20 configuration for street riders. In terms of real world examples, the billet master cylinder using in MotoGP is a 19x18 while the master cylinder includes with the Brembo High Performance street kits is a 19x20.

They don't take the calipers into consideration. The master cilinder should be matched to the calipers, or to be more accurate: the combined area of all the caliper pistons. The F3 calipers need a lot more brake line pressure to get the same brake force compared to the RC24 calipers (that have a 20% larger bore).

I disagree with slow2337 that radial master cilinder sizes do not corelllate to "conventional" master cilinders. Mechanicaly they are similar (master cilinders are always mounted radial to the pivot point), only the layout of the 'radial' master cilinder caters for simpler finetuning and adjustment as you can change pivot length by replacing the brake lever. Some radial master cilinders even come with adjustable pivot length. Also as the radial cilinder has less moving parts that results in more brake feel.

The (fixed) pivot length of 3rd and 4th gen MC is about 1".

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Veefer800Canuck Grand Master

Veefer800Canuck

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Stick as closely as possible to the OEM standard for M/cyl bore.

Radial master cylinder size numbers do not correlate to at all to the dimentions given for a standard type master cylinder. Using the size of a standard to pick the size of a radial is comparing apples to oranges.

Seb didn't say it was a radial master cylinder. He just said it's a Brembo brand.

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