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Discussion Starter · #1 ·
Looking to replace the clutch master on my 999 with a new radial one. It's my understanding the oem 9990has a 15mm piston. If I got a radial with a 16mm can I assume things will function properly?? Thanks.
 
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Looking to replace the clutch master on my 999 with a new radial one. It's my understanding the oem 9990has a 15mm piston. If I got a radial with a 16mm can I assume things will function properly?? Thanks.
If it's anything like brakes...larger piston, more volume pushed, less lever has to move...less effort....going up 1mm I would surmise as negligible...I went from a 16 to a 19 on the brakes...lever pull is appreciably lighter

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You got it the wrong way around. Smaller master piston, more fluid moved. All things being equal. Lever ratio: the closer the piston is to the pivot point the more power produced and the more the lever.
 

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You got it the wrong way around. Smaller master piston, more fluid moved. All things being equal. Lever ratio: the closer the piston is to the pivot point the more power produced and the more the lever.
Pretty certain that the smaller the diameter the smaller the volume...smaller diameter pistons use a deeper cylinder to make up for the loss equating to a longer throw...in turn more modulation

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Discussion Starter · #5 ·
So will the lever pressure be about the same and disengage the clutch properly?
 

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So will the lever pressure be about the same and disengage the clutch properly?
I suppose that is the real question...if the radial is made for your bike than someone has already done the math...if not calculate the volume of the new master and compare it to the old ...if it's off by a large margin...you can be in for trouble...other than that it will engage a wee bit sooner than your use to with a wee bit less effort...just move the lever to suit


https://www.zx6r.com/racing/103106-master-cylinder-ratio-16x19-vs-19x16-vs-19x18.html?amp=1
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Pretty certain that the smaller the diameter the smaller the volume...smaller diameter pistons use a deeper cylinder to make up for the loss equating to a longer throw...in turn more modulation

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Mmmm....wording is confusing......
 

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Discussion Starter · #9 ·
For clutches they are just listed as 14, 16,17,19....... Not 16-18, like the front brake masters are.....
 

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thanks Strega for the chart/

great help.I have a 16 brembo radial clutch & stock slave-999s.works very well however the last 1/4" of pull hits the switch.front brake lever also hit the throttle unless its revolved 180* & the cables rerouted.
super ez to bleed with the lever bleeder as well.
 

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great help.I have a 16 brembo radial clutch & stock slave-999s.works very well however the last 1/4" of pull hits the switch.front brake lever also hit the throttle unless its revolved 180* & the cables rerouted.
super ez to bleed with the lever bleeder as well.
That is some real world answers right there...and before someone says to turn the adjustment knob to bring out the lever....that is the effect of a smaller pivot distance .ie x18 on the brake master...a x20 would have less travel and give the clearance needed while maintaining the same amount of reach...I come across the same issue with mine (19RCS)...the same will hold true to the clutch but sounds like that isn't an option... nonetheless I don't believe anyone has their bite point that close to the grip so it's not really an issue

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If it's anything like brakes...larger piston, more volume pushed, less lever has to move...less effort....
This is incorrect.

Correct = "larger piston, more volume pushed, less lever has to move...more effort is required".

Less distance the piston must move to displace the same amount of fluid between a smaller cylinder and a larger cylinder, the greater the human effort required at the lever to do the same amount of work.

You got it the wrong way around. Smaller master piston, more fluid moved. All things being equal.
No. Smaller piston = less fluid displaced when moved the same distance as a larger piston. However, the smaller piston requires less effort by the human hand to move the slave piston a given distance.

If (let's say) a 19mm diameter piston is moved (let's say) 5mm, it will displace more fluid than an 18mm diameter piston if it too is moved 5mm. Note I said piston, not lever.

However, the less the lever has to move (due to the larger piston) MORE effort at the lever is required to get the slave to move the same amount of distance to do it's work. There's less movement by the lever required with the larger piston/cylinder, sure, but more effort by the human hand on the lever is required to move the slave the same distance as the smaller piston/cylinder.

It's the same as using a 2x4 piece of lumber to pry up a stone. Place your hands at the end of the board and you'll have to move the board a greater distance to lift the stone up 1 foot than if you place your hands halfway up the board to lift the stone up one foot ... however ... you'll have to exert yourself far more to lift the stone that same 1 foot with your hands halfway up the board. Don't confuse yourself by thinking of the board as the clutch or brake lever ... think of the board and it's length as the piston/cylinder.

This is all just High School level physics.

ADDITIONALLY: It's important to note that it's very likely manufacturers of various clutch/front brake master cylinders will engineer the levers and their pivot points so that larger hydraulic master cylinders (which move more oil when moved the same distance as smaller diameter master cylinders) feel as light or lighter than stock master cylinders.

The levers' pivot points and other associated geometry of the levers and their pivot points are moved around a bit to (perhaps) provide the perception of less effort to apply braking force or to disengage the clutch. When a larger master hydraulic cylinder is used, greater force on that piston is required to perform the same amount of work. So there's a very good chance that to compensate for the increased amount of effort the geometry of the lever and it's pivot point have been engineered to reduce (or just compensate for) the increased amount of force required to move the larger master cylinder's piston to displace the same amount of oil that a smaller piston requires.

That may be why some people erroneously think that a larger piston diameter will be "easier" to pull in than a smaller piston that's moving less oil per millimeter of movement .. when in fact it's actually a matter of the engineering of the lever's geometry.

In summary, a larger master cylinder piston does not equate to less effort to pull the lever in. The larger cylinder moves more oil with less movement, which means more effort will be needed to produce the same amount of work. To compensate for that, the lever's pivot placement is engineered to provide more leverage, which will produce less perceived "pull strength" to activate the brakes or disengage the clutch.

It's important to not conflate the two things (cylinder displacement and lever geometry).

Ok ... all done. :wink2:
 

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I converted to Brembo 16x18 on the clutch side and 19x18 on the brake side with Rizoma reservoirs. By moving the lever assembly around and pressure switch, the fit was excellent, no issues. I did this maybe five or six years ago and now I forgot how the stock set up differed, whether harder or softer. All I know I was happy with the conversion in all respects.
 
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I converted to Brembo 16x18 on the clutch side and 19x18 on the brake side with Rizoma reservoirs. By moving the lever assembly around and pressure switch, the fit was excellent, no issues. I did this maybe five or six years ago and now I forgot how the stock set up differed, whether harder or softer. All I know I was happy with the conversion in all respects.
Rex Coil & and John are correct in all respects. I just bought a 998 and I hated the masters - the brake I could lock up almost with one finger and grabby, and the clutch was like a race clutch, taking about 1mm to engage and making me twitch the back end out sometimes.

I made exactly the same changes as John and got the same excellent results, especially the clutch, which now seems to engage over a longer distance of lever travel and is much easier to use smoothly. Critical, with no traction control or slipper (yet). It did take some time to work out the new control ergonomics, but it was well worth the time.

Just my two cents. -Gordo
 

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