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changing from standard MC to Radial

Discussion in 'WERA Vintage' started by Doc_Rot, Nov 12, 2020.

  1. Doc_Rot

    Doc_Rot Active Member

    I am in the process of switching to clip-ons on a bike, the standard style master cylinder will not fit in the new configuration. I'm pretty sure there will be plenty of room if i switch to a radial MC design. The bummer is right now the brake setup is fabulous. Dual Grimeca replicas of Lockheed 41mm twin piston calipers and a 16mm brembo MC with a 22mm bore/pivot span. great feel and stopping power I don't really want to change it but that means the bars would have to be way too wide to accommodate.

    The problem is the closest radial MC I can find is a 16mm with a 18mm lever offset. It seems like this setup will have significant mechanical advantage over the last one because of the smaller offset and a longer lever.

    Should I go to a 17mm radial with a 18mm lever offset to compensate? Any experience switching from standard to radial MC?
     
  2. Boman Forklift

    Boman Forklift Well-Known Member

    I don't know the answer to your question. However, is there a chance with a longer bar, that slides into the clip-on further, you could bolt the master onto the other side of the fork tube and then squeeze onto the very end of the lever vs. the beginning or middle of the lever in your current setup?

    I know on one bike we put my sons as far up as possible so he could squeeze towards the lever end as he liked the control/feel better that way.
     
    RRP and TurboBlew like this.
  3. Doc_Rot

    Doc_Rot Active Member

    thanks for the reply. I have woodcraft side-mount clipons so the bar terminates perpendicular to the fork tube - no room to scoot it up.
     
  4. Busdriver02

    Busdriver02 Well-Known Member

    Take the total surface area of the pistons combined and divide by the surface area of the M/C to get hydraulic ratio.
    Then take the distance from the brake lever pivot to where your finger touches the lever and divide that by the pivot to M/C distance
    Multiply those numbers together to get the overall ratio. Bigger=more power, less firm.

    Assuming 115mm from pivot to hand (about what my bike is) and I hopefully didn't screw up the math....
    Your current setup 16x22 is 137 overall
    18x18 is 132 overall
    17x18 is 148 overall.
    16x18 is 167 overall
     
  5. Doc_Rot

    Doc_Rot Active Member

    I had the hydraulic and mechanical ratios worked out thanks to these Brembo diagrams, but I was struggling in how to relate them to one another. the current lever is much shorter than the radial one resulting in a very different mechanical advantage. currently the lever is about 85mm from pivot to pull point which is what originally had me concerned about this.

    16x22 - is 107
    17X18 - 148
    17X20 - 133
    19x18 - 117
    19 x 20 - 107

    by this math it seems like a 19 x 18/20 might be the way to go?

    The one thing that give me pause is in the description for the Brembo 17RCS it says it was specifically created for the Brembo M50 which uses (4) 30mm pistons. dual calipers put it at a 24.8/1 hydraulic which is what i was told was close to ideal. 25-27 being ideal.

    Screen Shot 2020-11-12 at 8.42.44 PM.png Screen Shot 2020-11-12 at 8.42.21 PM.png
     
  6. Busdriver02

    Busdriver02 Well-Known Member

    Sorry, I was running on no sleep last night and the brain was seriously mis-firing. I was using two different spreadsheets and jumbled up a bunch of stuff.

    You're going to get a much higher overall advantage with a radial MC, so that's a bad comparison on my part.

    I have an RC51 with weird 30/32 calipers, I did the same thing you alluded to by comparing the calculated ratios to a recommended combination. It seems like the radial combos have hydraulic ratios that are a touch lower and rely on mechanical advantage.

    In my case I went with a 17RCS, set to the 20mm setting it works well. The 18mm setting has a pretty long travel. If I were doing it again, I'd probably buy an 18mm magura. But they're pricey.
     
  7. Doc_Rot

    Doc_Rot Active Member

    I talked to the Brembo distributor for USA and they recommended the 17 so i have ordered one. They told me its better to have more mechanical advantage rather than hydraulic. You can crunch numbers all day but ultimately you gotta test it. I will report back - hopefully you wont see it in the for sale section!
     
    Busdriver02 likes this.
  8. Rich Graver

    Rich Graver Well-Known Member

    I tried it once on a 89 GSXR front end. I don't recall the diameter of the MC but it was NOT confidence inspiring. It came back off cause the lever was going to the bar and it was bled.
     
  9. Doc_Rot

    Doc_Rot Active Member

    I had dual brake lines coming from the master so i changed to single line with a splitter, messed with the angle of the handle bars and ground down the master a little bit and i was able to get the room I needed. I never tried the radial.
     

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