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
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.
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.
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.
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...
I'm no expert nor related to Nicky Hayden or Rossi or whoever but from what I've learned from others I think know what they're doing on a bike and read elsewhere, it comes down to finding the ratio sweet spot combined with stiffness that offers you feedback you can feel at the lever.
Back to the sweet spot, too much ends up feeling "wooden" to a little "spongy" for the spectrum. The point is they won't talk (feedback) to you too well. "Wooden" means easy to lock up to me because you won't feel it before lockup, so if you want to slide it, go this way.
Let's neglect stiffness and lever ratio and only look at master cylinder to piston ratio to get you to a starting point. I know what others have told me on sport bike front brakes but I've never discussed the rear, so I had to go find something on this. The opinions seem to indicate you care if it has 1 or 2 rotors, pistons on 1 side of the rotor or both (# of pistons?) in what ratio you might pursue.
From above (earlier posts) I think we've covered the more ideal ratio on the front. If you have pistons on both sides on rear caliper, I'd personally consider chasing the same ratio. If it is only one piston, I'd consider half that ratio.
That said, I suspect you will find it easier to find substitute master cylinders over calipers to find your sweet spot.
This might all be useless advice, so be careful with what you do with it and good luck.
At the risk of agreeing and disagreeing with you at the same time, you are quite correct in that the travel (stroke) will change (it's a volume thing where if you decrease the bore, you increase the piston stroke to move the same amount of fluid to move the same piston the same amount, which there is also an inverse to). However, feel isn't easily quantified with straight math or physics. This is the part I'm attempting to communicate my understanding of.
For me it all comes down to load path and stiffness. In this case mechanical and hydraulic stiffness. Mechanical design of the components plus the ratio in master cylinder to caliper piston ratios for the hydraulic and it's mostly static but with a dynamic component. Hence the sweet spot ratios. My apologies for lacking a better explanation.
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