Just leaned something new about the RC51 front brakes - Honda RC51 Forum : RC51 Motorcycle Forums
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post #1 of 15 (permalink) Old 01-01-2016, 05:54 AM Thread Starter
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Just leaned something new about the RC51 front brakes

I have a SP1 I was looking to rebuild the front master cylinder. During the research I discovered the SP1 master and calipers have bigger pistons than the SP2.



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post #2 of 15 (permalink) Old 01-01-2016, 07:35 AM
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That's interesting. Does anyone here with experience with both Sp1's and Sp2's know if there's a performance difference with the brakes between the two bikes?

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post #3 of 15 (permalink) Old 01-01-2016, 11:38 AM
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It's a fact that the SP1 caliper pistons are bigger. I know I've read it before in this forum from @SubSailor @LDH and other fellas...
Obviously, Honda went with smaller pistons on the SP2 for weight savings.

However, if you need to find out which setting has more powerful bite on the rotors, it's not only about the piston diameter you need to know about but the m/c piston diameter and the relative stoke of each piston when engaged

Like I've mentioned in previous post:






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post #4 of 15 (permalink) Old 01-01-2016, 12:23 PM
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post #5 of 15 (permalink) Old 01-01-2016, 12:33 PM
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I'm new to these bikes, so please feel free to verify anything I say.

I've read, and been told, that they are different. The SP-1s were 2mm larger at the caliper and the master cylinder. The front rotors are also 0.5mm thinner on the SP-1s.

Is the SP-1 better? Doubt it for an average rider, one can argue the SP-1 is superior from a braking power standpoint. The SP-2s were basically SP-1s with all the revisions learned racing the SP-1s. In the end this might be a difference without a distinction for most riders. Unless you are used to pushing limits on the front brakes going into turns and can feel the feedback at the lever, doubt most of us mere mortal riders will be able to tell.

That said, I'm planning to upgrade my master cylinders in the hopes feeling the feedback more. I have an SP-1, so I'm going with a 19mm master.

Just my 2 cents, which is about what it might be worth.

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post #6 of 15 (permalink) Old 01-01-2016, 12:51 PM
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being bored, i crunched the #s

the sp1 overall caliper/master ratio is 23.986

the sp2 overall caliper/master ratio is 25.713

sp1 master with sp2 calipers is 21.358

sp2 master with sp1 calipers is 28.877



it's basically a wash. the higher the ratio the easier the pull, but it's marginal at best. at the end of the day, braking power is down to the amount of friction that the pads can put on the rotors. how hard you have to pull the lever is up to you. these ratios are more about feel than absolute power


a lot of people misconstrue the meaning of "braking power" and equate an easy pull with powerful brakes, which isn't necessarily the case.
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post #7 of 15 (permalink) Old 01-01-2016, 12:58 PM
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It's not about weight savings (which would be negligible), but about brake feel (mechanical leverage).

The SP1 had less leverage, with more force required for braking, with less lever travel.
The SP2 has more leverage, with less force required for braking, with more lever travel.

Pads being equal, the SP1 may have a more progressive feel, while the SP2 has more braking force.

It all boils down to personal preference, as Brembo and others have master cylinders with selectable lever pivot positions to change leverage ratios.

The important take away is to be aware of WHICH master cylinder/caliper is used when replacing piston seals, and to order the correct parts!
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post #8 of 15 (permalink) Old 01-01-2016, 02:24 PM
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In the end, I have to agree with other commenters, it's probably a wash for us mortals but there is some argument for better feedback on the SP-2 ratios, depending on what ends up being truly better feedback (someone like Nicky Hayden is worth asking).

Another way to obtain better feedback is by increasing stiffness assuming one's ratios are in the sweet spot. Radial calipers and master cylinders are how one does this. Again, they will improve it but only if you can tell, which is more a skill than an engineering exercise.

Another way, mentioned above, is to change your lever ratio which really affects how fast you get your braking power for how hard you have to squeeze (master cylinder does this too).

Now wrap all of this up and you have a system with many variables. The combination of those variables determines how good it is for what you are doing. By all accounts, the stock brakes on these bikes ('00 thru '06) are quite good. Just keep the master cylinders lined up with the right calipers and I'm thinking we should be good. I'm just going to tweak my master cylinders and call it a day. I already have good lines that run from the master cylinder to each caliper.

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post #9 of 15 (permalink) Old 01-01-2016, 03:55 PM
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Excuse me for pirating this thread but I have been trying to understand this stuff too.
I want to change the feel of the rear brake so I started doing some research on hydraulic theories with regard to motorcycle brakes. If someone can help prove or disprove this please feel free to speak out. As an example, If a 12mm rear master is used with a 32mm caliper and you decided that you want more clamping force to lock the rear tire then going down to a 10mm master cylinder would do this but would also give less feel. Conversely if you wanted more feel and less locking power a 14mm master would do this. For the caliper, it seems to me then, if you left the master cylinder alone, and changed to a larger piston caliper you would have more clamping force and less feel and a smaller piston caliper would then have more feel with less locking power because the surface area of the caliper piston is less. If anyone has ever experimented using different sized piston calipers or master cylinders or knows about this stuff, please...
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post #10 of 15 (permalink) Old 01-01-2016, 05:38 PM
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it's not about feedback its about lever travel

if you increase the slave/master ratio you increase lever travel, if you decrease it decrease lever travel


yes effort required changes but not immensely
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