Author Topic: Brake input  (Read 751 times)

HornetMaX

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Re: Brake input
« Reply #15 on: March 08, 2018, 07:03:19 PM »
...so while I've done a few m/c swaps, they've been more about improving the quality of the unit rather than adjusting the travel/lever force.  The earlier ones were all about the same size, had about the same travel and took about the same force.  It wasn't until the calipers were changed that there was less force required at the same travel.
Yeah, hard to compare if the quality is changing. But when you say "bigger pad/pistons ==> less force required" the you're also saying "smaller MC ==> less force required".
BTW, what would justify the quality difference between the different MC in your opinion ? I have my idea ... :)

And you're still factoring in travel in the overall feeling: probably makes sense in real life, but not in GPB.
In GPB it seems to be a simple "input displacement vs braking force" relationship: smaller MC = steeper line.
(I say seems as I thought disc thermals where somehow simulated, no longer sure since PiBoSo last comment).

h106frp

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Re: Brake input
« Reply #16 on: March 08, 2018, 07:18:59 PM »
I think where we are coming unstuck is that we do not model the caliper piston numbers and diameters so we can go to a theoretically small MC without any unwanted side effects that would occur in real life as we struggled to shift enough volume to drive the pistons or too large in MC and end up with on/off braking and no modulatiion range.

Grooveski

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Re: Brake input
« Reply #17 on: March 08, 2018, 07:54:18 PM »
Yeah, hard to compare if the quality is changing. But when you say "bigger pad/pistons ==> less force required" the you're also saying "smaller MC ==> less force required".
BTW, what would justify the quality difference between the different MC in your opinion ? I have my idea ... :)

Bigger pads increase the overall efficiency of the system - you need less pressure on the lever to achieve the same braking force becuse there's more friction at the end.

Assuming the m/c matches the calipers of course.  When I changed calipers I didn't even try the new ones with the old m/c because it'd have been too soft at the lever - so I increased the m/c size at the same time to give the same amount of travel.

As for quality - that's more about feedback/feel.  The R1 Radial m/c didn't affect how hard I could brake compared to the one that came with the bike but totaly affected the feel. 
The lighter return spring and more direct plunger direction of a radial m/c probably played the biggest parts but I'm sure if there was a Brembo employee here he'd be telling us about the bore surface treament/o-ring materal/alloy perosity.....  ;D
Was 60 well spent in my view and done me fine for a few years.

...but I was riding other bikes too in that time, and they pretty much all had better brakes that the wee zxr - so I decided on the caliper upgrade.

Even before I started faffing around I'd replaced the hoses with braided affairs and the pads for hh sintered.  Now the only component that's original is the little splitter that branches the hoses mid-line.   ::)

HornetMaX

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Re: Brake input
« Reply #18 on: March 08, 2018, 08:46:18 PM »
I think where we are coming unstuck is that we do not model the caliper piston numbers and diameters so we can go to a theoretically small MC without any unwanted side effects that would occur in real life as we struggled to shift enough volume to drive the pistons or too large in MC and end up with on/off braking and no modulatiion range.
Why you say that with a large MC you have no (or less) modulation range ?! You're still reasoning in terms of lever displacement I guess.
In terms of lever pressure, with a large MC you've more modulation (lesser slope in the curve between lever pressure and braking force).

But what you said may also be a reason why the input is lever force instead of lever travel: travel would need some additional params about the pistons sizes and number (even if to me, the real justification is that even on a real bike, you work more in terms of force than in terms of travel).

Anyway, all this becomes mostly academical given that you can tune the input deadzone, linearity and gain, indepenently on whichever physics settings of MC, levarage etc. :)

Bigger pads increase the overall efficiency of the system - you need less pressure on the lever to achieve the same braking force becuse there's more friction at the end.
In principle (and at a simplified level), this is wrong: kinetic friction force depends on the normal force (and friction coeff), not on surface.
The normal force is the circuit pressure times the total pistons area, so that doesn't change when you change the pads.
Bigger pads may have other advantages of course (like thermals or wear).

As for quality - that's more about feedback/feel.  The R1 Radial m/c didn't affect how hard I could brake compared to the one that came with the bike but totaly affected the feel. 
The lighter return spring and more direct plunger direction of a radial m/c probably played the biggest parts but I'm sure if there was a Brembo employee here he'd be telling us about the bore surface treament/o-ring materal/alloy perosity.....  ;D
And I'd tend to believe him (well, up to a point): it may well be that the perceived quality is mostly driven by how "rigid" all the components are (MC, hoses, calipers etc) than anything else.

Grooveski

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Re: Brake input
« Reply #19 on: March 08, 2018, 09:24:07 PM »
In principle (and at a simplified level), this is wrong: kinetic friction force depends on the normal force (and friction coeff), not on surface.
The normal force is the circuit pressure times the total pistons area, so that doesn't change when you change the pads.

The calipers with the bigger pads had bigger pistons. 
Kinda thought that went without saying - Otherwise I wouldn't have had to change the m/c to match.

HornetMaX

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Re: Brake input
« Reply #20 on: March 08, 2018, 09:33:50 PM »
In principle (and at a simplified level), this is wrong: kinetic friction force depends on the normal force (and friction coeff), not on surface.
The normal force is the circuit pressure times the total pistons area, so that doesn't change when you change the pads.

The calipers with the bigger pads had bigger pistons. 
Kinda thought that went without saying - Otherwise I wouldn't have had to change the m/c to match.
OK, makes more sense. But then it's not so straightforward that the modified system will give higher efficiency (lower force on the lever for the same braking force), as for the same lever force, the bigger MC will generate a smaller pressure: yes, this could be compensated by the bigger pistons, but the overall result will depends on the exact numbers (it could go either way).

Grooveski

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Re: Brake input
« Reply #21 on: March 08, 2018, 10:02:20 PM »
(it could go either way).

Yeah - My dad found that with his second Blackbird(or maybe it was the second 'Busa  :-\ - he's had two of each) - Huge great 6 pot calipers with acres of pad but he felt the old 4 pots had better bite.

In the zxr's case it was just underbraked to begin with.  When Kawasaki changed from the H to the L model they upped the disks from 300 to 310...
...but for some reason changed the calipers from 4x30 & 4x28 to a set with 8x27mm pistons (and pads only about 3/4 of the area of the earlier model).

The newer calipers were smaller so a fair bit lighter(probably the main factor in their decision) but I've noticed no ill effects since bolting on the heavier ones.
If they'd stuck with the same calipers (and the matching 14mm m/c) from the earlier model I'd have likely never even thought about upgrading anything.

Of course then I wouldn't have a lovely RCS19 at my fingertips - which I must admit puts a smile on my face with it's looks as well.  ;D
Not 200's worth of smile though.     ;)  Thankfully it works as good as it looks.
« Last Edit: March 08, 2018, 10:12:10 PM by Grooveski »