Radial master cylinder part 2 - Wrist Twisters
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post #1 of 6 Old 06-21-2012, 04:59 PM Thread Starter
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Radial master cylinder part 2

A while back I got an aftermarket 16mm radial master cylinder for next to nothing (about $40 with shipping) and threw it on. See the thread here: https://www.wristtwisters.com/forums/...ers-25724.html. While it did work fairly well the overall ratio was too high, 173:1 compared to the 120:1 stock, consequently it took a lot of lever movement to engage and always felt spongy: a common problem with too high a ratio. The braking effort was significantly reduced, but it just never felt right. Then it started to leak out of the secondary seal so I trashed it and reinstalled the stocker.

Well, I was not satisfied with the way things turned out and was determined to give it another go. Lo and behold I found an '07 CBR1000 master on Ebay and got it for $57! It has an 11/16" (17.46mm) bore and an interaxis ratio of 118 / 18, shaking out to an overall ratio of 135:1: much better than my previous try! After completely tearing it down and inspecting all the internal components -- they showed no wear at all and the bore looks like it had never been used -- I swapped it in. All that was left was to machine a new reservoir feed fitting from a scrap of 7075 T6 I had lying around to replace the broken plastic piece, knock out a quick outlet manifold for my AN fittings, replace the inop brake light switch, and mount it up. It took ~ 3 minutes and 15cc's of fluid to get a rock hard lever (It's good being an expert!) and it was ready to go for a ride.

In a word: very nice! The lever feels slightly more firm than the stocker, partly due to shimming the piston for better proximity to the compensating port, and it's practically one finger regardless of how badly you may need to stop. Even howled the front tire with one finger: a first for this system.

Another thing -- notice the lever. Yup, it's a CRG shorty which probably costs more than I paid for the whole shebang. How could I not get it?

That's it for now. I'm going for another ride.

Rob
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post #2 of 6 Old 06-21-2012, 06:59 PM
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Now that is interesting. Off to eBay to set up a search for CBR1000 master cylinders!

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post #3 of 6 Old 06-21-2012, 10:05 PM
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i must ask.... what is the benefit of a radial master cylinder?

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post #4 of 6 Old 06-22-2012, 12:07 PM Thread Starter
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Quote:
Originally Posted by nd4spdbh View Post
i must ask.... what is the benefit of a radial master cylinder?
They're trick. Well, there's more to it than that.

The most significant difference between a radial and axial (conventional) master cylinder is the hydraulic ratio is quite a bit lower than the axial setup: for the same calipers the ratio is 33:1 for a 14mm bore axial versus 20:1 for an 18mm bore radial, both feeding two four piston calipers with bores of 30.15mm and 27mm . The difference is made up in the mechanical ratio, ~ 3.6:1 for a axial versus ~ 6:1 for a radial. On axial master cylinders the lever is a right angle bellcrank so the cylinder axis is parallel to the handlebar, whereas the radial type lever is just a straight lever and the cylinder is at right angles to the handlebar. There is a fallacy here: proponents of the radial type tout the "direct" nature of the lever makes for a smoother actuation, but in fact I have made axial master cylinders that are every bit as smooth -- it just takes attention to the small details regarding the piston actuation, which on axial units is usually a rounded end scanning against the piston face versus a ball jointed rod actuating the radial piston. A disadvantage of a radial is the very short pistons with bearing surfaces quite close to each other, making the angle of the pushrod at the mean actuation point quite critical to avoid thrust loads on the rear bearing surface and attendant drag against the cylinder wall causing excessive wear. The only real advantage to a radial is it takes up much less handlebar space, which on a road racer with very narrow handlebars can be a large advantage aerodynamically.

Of course there is another difference -- practically no radial types have an integrated reservoir. Not a problem if they are on clip ons and there's a fairing to hide the barnaclesque reservior, but if you are looking for a clean setup on a naked bike it can be nearly impossible.

There you have it. The main reason why I am using a radial is to get a slightly higher overall ratio to decrease effort at the lever and increase the engagement band, which makes holding the brake just this side of locking up a bit easier. Of course you can go too far with this -- the 16mm radial I used previously had a mile wide engagement band, but the lever was so soft it was exceedingly difficult to modulate near locking consistently.

Rob

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post #5 of 6 Old 06-22-2012, 03:05 PM
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Sounds awesome though!

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post #6 of 6 Old 06-22-2012, 06:14 PM
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Quote:
Originally Posted by robtharalson View Post
They're trick. Well, there's more to it than that.

The most significant difference between a radial and axial (conventional) master cylinder is the hydraulic ratio is quite a bit lower than the axial setup: for the same calipers the ratio is 33:1 for a 14mm bore axial versus 20:1 for an 18mm bore radial, both feeding two four piston calipers with bores of 30.15mm and 27mm . The difference is made up in the mechanical ratio, ~ 3.6:1 for a axial versus ~ 6:1 for a radial. On axial master cylinders the lever is a right angle bellcrank so the cylinder axis is parallel to the handlebar, whereas the radial type lever is just a straight lever and the cylinder is at right angles to the handlebar. There is a fallacy here: proponents of the radial type tout the "direct" nature of the lever makes for a smoother actuation, but in fact I have made axial master cylinders that are every bit as smooth -- it just takes attention to the small details regarding the piston actuation, which on axial units is usually a rounded end scanning against the piston face versus a ball jointed rod actuating the radial piston. A disadvantage of a radial is the very short pistons with bearing surfaces quite close to each other, making the angle of the pushrod at the mean actuation point quite critical to avoid thrust loads on the rear bearing surface and attendant drag against the cylinder wall causing excessive wear. The only real advantage to a radial is it takes up much less handlebar space, which on a road racer with very narrow handlebars can be a large advantage aerodynamically.

Of course there is another difference -- practically no radial types have an integrated reservoir. Not a problem if they are on clip ons and there's a fairing to hide the barnaclesque reservior, but if you are looking for a clean setup on a naked bike it can be nearly impossible.

There you have it. The main reason why I am using a radial is to get a slightly higher overall ratio to decrease effort at the lever and increase the engagement band, which makes holding the brake just this side of locking up a bit easier. Of course you can go too far with this -- the 16mm radial I used previously had a mile wide engagement band, but the lever was so soft it was exceedingly difficult to modulate near locking consistently.

Rob
gotcha thats what i figured... i mean they are trick small and look cool but only really offer better mechanical advantage at the lever due to the fact you can have the lever pivot point and piston location closer together than your standard master cylinder thus increasing your overall mechanical ratio.

And rob +1 to your infinite wisdom!
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