Gen 2 clutch spring recommendations

[ZeePopo]

So I'm ordering a STM slipper clutch and wasn't sure what primary spring pressure on a road racing stock Busa I should be running. It comes with a 190kg spring which is around 420 lbs. It only uses one spring on the clutch pack, the secondary spring is for the slipping function. It seems that even on lower HP bikes than the Busa also come with the 190kg spring. So the question is are these other bikes oversprung on the clutch or is the Busa undersprung. I can have them change the primary spring before shipping. Strongest they have is 230kg which is 507 lbs.

[rubbersidedown]

I am by no means an expert on those types of clutches. Does STM offer a heavier primary spring for motors with higher horsepower than stock (like turbo applications) ? I know riders who beef up stock clutches with heavy springs often complain of the extra force needed to pull the lever. I would also consider the extra force which will be exerted on the slave housing, an already weak link in a Busa clutch in my opinion.
When you say "road racing stock busa" what does that mean? What are you doing with your bike? Track bike?
Is it aggressive downshifting you are concerned about? What are STM's claims that make you want to go this route? As the engine brakes these clutches use ramping to ease wheel speed down but then also apply more force than stock under hard acceleration.
If as mentioned the primary spring has no effect on the slipper action,why the different spring options? The heavier spring sounds like it is about 20% stiffer...thats a lot if you ask me. Will this slipping action chew up a clutch at a faster rate?
Again...I know nothing...but would like to learn.
Rubb.

[Hayabusa Wannabe]

@rubbersidedown what about increasing the master cylinder size to ease the burden? Is heft really an issue on a hydraulic system?

[rubbersidedown]

@rubbersidedown what about increasing the master cylinder size to ease the burden? Is heft really an issue on a hydraulic system?

For sure an' increased master would work,just as it does for upgrading Busa brakes. Less lever pull force is achieved while force is increased on calipers...or in this case,the slave.
I have rode old Harleys with heavy cable clutches and for me on any bike,the amount of force needed on a clutch lever has never been a concern/issue.I think its mostly the high miler touring guys who presented the complaint. I have a fairly heavy duty MTC 2-stage lockup clutch and I feel no diff between it and stock. My clutch pack is designed to handle 500+ HP so I imagine the springs are fairly stiff. I can wiggle my Busa threw all sorts of low speed stuff using clutch control to easily maneuver and have never had issue,nor with 8 hours in the saddle. I barely touch the clutch on most up or downshifts anyway...its more like pretending to squeeze it.
Rubb.

[ZeePopo]

I am by no means an expert on those types of clutches. Does STM offer a heavier primary spring for motors with higher horsepower than stock (like turbo applications) ? I know riders who beef up stock clutches with heavy springs often complain of the extra force needed to pull the lever. I would also consider the extra force which will be exerted on the slave housing, an already weak link in a Busa clutch in my opinion.
When you say "road racing stock busa" what does that mean? What are you doing with your bike? Track bike?
Is it aggressive downshifting you are concerned about? What are STM's claims that make you want to go this route? As the engine brakes these clutches use ramping to ease wheel speed down but then also apply more force than stock under hard acceleration.
If as mentioned the primary spring has no effect on the slipper action,why the different spring options? The heavier spring sounds like it is about 20% stiffer...thats a lot if you ask me. Will this slipping action chew up a clutch at a faster rate?
Again...I know nothing...but would like to learn.
Rubb.

Yup getting the slipper clutch for track riding and agressive downshifts. Yeah slipping will wear the clutch pack faster. Price to pay I guess.

[Berlin Germany]

@rubbersidedown what about increasing the master cylinder size to ease the burden? Is heft really an issue on a hydraulic system?

it helps at your left hand if you make the dia (lowering) of the master´s cylinder 1 mm smaller from 5/8 = 16 mm to 15mm (or you use a 16mm radial pump wich has other ratios at the lever than the original 5/8)
have a short thought about ratio.
"comparable to making a lever longer and thinking that the cabinet you want to lift will be lighter"
but the master has no influence to the clutch itself and the force you have to put into to get it "open" / engaged (?).
the spring and her force stay the same.

very hard to describe here in written words - sorry

[Hayabusa Wannabe]

Good stuff @Berlin Germany. So many here install Brembo masters which are inherently radial, so what was in my brain came out wrong. You fixed that with good comprehensive advice, perfect.

[ZeePopo]

it helps at your left hand if you make the dia (lowering) of the master´s cylinder 1 mm smaller from 5/8 = 16 mm to 15mm (or you use a 16mm radial pump wich has other ratios at the lever than the original 5/8)
have a short thought about ratio.
"comparable to making a lever longer and thinking that the cabinet you want to lift will be lighter"
but the master has no influence to the clutch itself and the force you have to put into to get it "open" / engaged (?).
the spring and her force stay the same.

very hard to describe here in written words - sorry

I'm running a 14mm on clutch so im good