clutch pull - wet vs dry

[mikeb]

Got a question about clutch pull - wet vs dry.  What is the primary reason for the different clutch pull?  Different bore master/slave?  Lighter springs?  Due to the oil?  Combination of all the above?

Just moved back to a dry clutch bike and forgot how stiff that damn clutch was.  Got a slave cylinder coming and was thinking of pulling some of the springs.  Thinking of the options got me wondering what makes the wet clutch bikes easier.

My assumption is possibly softer springs.  With less hp and torque maybe the smaller cc bikes can get way with light springs.  Just a guess....

Any ideas?

[Triple J]

I don't know the answer, but it ain't horsepower. Japanese liter bikes have a shit ton of it, and a light lever.

My 748 with a slipper also has a very light pull. 

[Spidey]

There are different wet clutches.  There's the APTC (or whatever the hell that acronym is) and the older, non-slipper wet clutch.

[mikeb]

I don't know the answer, but it ain't horsepower.

I know it's not horsepower per se.  Just that the large cc bikes get the dry clutch...and stiff pull.  So wondering if its a function of the clutch...or if Ducati specs a stiffer spring for the bigger bikes.

As for your slipper they work differently than a standard clutch because they are designed to slip.  I've read of people taking 2 spings off their dry clutch for s lighter pull and had their clutch start slipping.

But it brings up an interesting point.  Wonder what makes you slipper lighter than a stock dry clutch?

[mikeb]

There are different wet clutches.  There's the APTC (or whatever the hell that acronym is) and the older, non-slipper wet clutch.

True.  But I've spent time on both the old wet clutch and the new APTC (or whatever) and they are both easier than the dry clutch bikes I've owned. 

I'd gladly put a new APTC wet clutch in my S2R 1000. 

[scott_araujo]

The slots in the basket for the clutch plates in the slipper clutch are angled or 'ramped', not parallel with the crankshaft.  Incorrect, please see below.  When you apply torque from the engine it basically screws itself tighter creating more pressure than the springs alone provide.  Conversely, when you're engine braking and the wheel is driving the engine, it's going the other way and can unscrew itself a bit creating less pressure.  Due to this dynamic, not all of the clutch pressure for acceleration comes from the springs and so the springs can be lighter and it still won't slip under acceleration.  Also, when you downshift too far and send huge engine braking torque into the clutch, it unscrews a little and creates lighter pressure allowing the clutch to slip and keep the rear wheel from sliding.

I have the '03 800 with a regular wet clutch and it's stiff.  Nothing terrible but it takes some getting used to at the beginning of the riding season and gets annoying in stop and go traffic.  When I squeezed the clutch on the 696 my jaw dropped.  I couldn't believe how light it was by comparison.  Never compared it to something like the S2R with the same motor but the APTC (or whatever) slipper.  I prolly should.

Scott

[mikeb]

not all of the clutch pressure for acceleration comes from the springs and so the springs can be lighter and it still won't slip under acceleration.

Thats what I was thinking...they used lighter springs either by design or simply because they can without slipping.

I have the '03 800 with a regular wet clutch and it's stiff.

I had an '03 620 and the clutch wasn't bad at all.  But no where near as nice as the 696.

[He Man]

i tthough the slippers are easier to pull cause some of the weight is resting on the ramp/ or bearings instead of being held open purely by the clutch lever?

[sbrguy]

the 03 620 clutch pull when compared to even the 695 clutch pull was noticeably heavier, the 695 clutch pull as is the 696 clutchpull is very very light, almost to the point i think its "too light"

[Langanobob]

The slots in the basket for the clutch plates in the slipper clutch are angled or 'ramped', not parallel with the crankshaft.  When you apply torque from the engine it basically screws itself tighter creating more pressure than the springs alone provide.  Conversely, when you're engine braking and the wheel is driving the engine, it's going the other way and can unscrew itself a bit creating less pressure.  Due to this dynamic, not all of the clutch pressure for acceleration comes from the springs and so the springs can be lighter and it still won't slip under acceleration.  Also, when you downshift too far and send huge engine braking torque into the clutch, it unscrews a little and creates lighter pressure allowing the clutch to slip and keep the rear wheel from sliding...

Scott

Scott, great explanation.  Thanks,
Bob

[DesmoReynoso]

I love my APTC Clutch on my 696!!!  [moto]

[scott_araujo]

I was looking for the pics I saw a few weeks ago to give He Man a better idea of what's going on and I think the way I described it was wrong.  The basket slots are still parallel to the crank.  In addition to the springs there are some ramps and bearings that also press on the clutch plates.  Here are some nice pics of a slipper clutch that I hope help: http://www.yoyodyneti.com/motorcycle_slipper_clutch_operat.htm

When the engine drives the wheel, the ramps & bearings add extra pressure by screwing down on the plates.  When you engine brake and the wheel drives the engine, the ramps & bearings open up and provide less pressure.  Sorry to spew misinformation above, I saw an image of a slipper basket with angled slots a few weeks ago.  Maybe that was just some weird prototype.

Anyway He Man, what I wanted to explain is that if you have the clutch pulled in the ramps and bearings aren't doing anything.  They only come into play when there is tension in one direction or the other between the engine and the wheel.  BUT because the ramps and bearings provide more tension when accelerating the springs don't have to provide it all.  In a regular clutch the springs have to do all the work so need to be pretty stiff.  In a slipper some of the pressure is created by ramps and bearings so the springs can be weaker but you still get the same total pressure but with lighter lever pull.

In short, it's not that the weight is resting on the bearings when the lever is in, it's that the ramps and bearings create more pressure when the clutch is out and the bike is accelerating.  Make sense?

Scott

[He Man]

makes sense.    i have both the 749r bearingless slipper and a 6 bearing slipper side by side, and its only when compared to stock you feel the big difference.

[Langanobob]

Quote from Scott

I was looking for the pics I saw a few weeks ago to give He Man a better idea of what's going on and I think the way I described it was wrong.

Well, it fooled me and it was still a good explanation even if it was wrong 

[scott_araujo]

Same idea, different mechanism.  Fooled me too