| Author | Message | ||
     Bob_thompson |
I am trying to understand slipper clutches in sport type street driven bikes. These are now available in three major foreign bikes, being Kawasaki's ZX10, Suzuki's GSXR1000 and Yamaha's R1's. After having read why our XBRR's presumably failed at Daytona recently in a racing environment I wonder if there is any advantage for a street motorcycle if we hardly ever ride to the extreme of a racing environment, i.e. radically entering a hard turn to make the rear shudder with over engine braking. Does anybody have a valid reason why we would want such an item on our street bikes? It seems as though these might deter from long clutch life and limit our slowing down without braking. Whats your take on this. Thanks much, Bob (Message edited by bob_thompson on March 26, 2006) | ||
| Diablobrian |
take a look at the xb board in the xbrr area. A lot of this ground has already been covered. | ||
| Rocketman |
Those threads actually contained little to no technical information about slipper clutches actually, more was the pity. Rocket | ||
| 12r |
My background is in two-strokes and I owned an NS400R for 8 years and a RG250 for 2 years. Moving onto an IL4 and easing off the throttle for the first corner was like throwing a ship's anchor off the back and I found it difficult to achieve a smooth entry and mid-corner acceleration. Since the demise of two-strokes and carbs, FI has honed power deliveries and with 200 bhp on tap racers are finding it difficult to stabilise the motorcycle when braking/downshifting from high speeds and turning in. The slipper clutch allows the rider to select lower gears for a corner without having to worry about upsetting the motorcycle by mismatching the engine/wheel speed. On a belt drive Buell, on the road, a slipper clutch is completely unecessary - I ride for miles in the twisties without changing out of third or fourth gear. But I couldn't do this on a high-revving IL4 without dropping out of the power band. Having to match engine/wheel rpm before a downshift is a major pain on a free-spinning, high-rpm engine and if a slipper clutch allows two or three fast downshifts into a corner then it's all good. | ||
| Grndskpr |
I am trying to understand slipper clutches in sport type street driven bikes. These are now available in three major foreign bikes, being Kawasaki's ZX10, Suzuki's GSXR1000 and Yamaha's R1's Its standard on most of the Kawi line, including zx6, zx 10, and has been a stock item on the ZX7 since 1992, they refer to it as a back torque limiter, the issue with these bikes(at least the zx7) has been how its adjusted, and how to get the correct factory parts to adjust it correctly, which can be a pain Why on the street, no reason other than to eliminate wheel hop, with dramatic slow downshifts and slow down, there nice at places like the dragon, but worth less in chicago Hope that helps R | ||
| Jackbequick |
I was trying to see what the racers were doing with their clutch hands during the Moto-GP yesterday but it is hard to see enough detail. I could see a little in that low gear corner where they sit upright and then make a swoop right. The clutch action there for some was a rapid three or four clutch squeezes just before they started the turn and got back on the gas. Didn't seem to be much visible throttle blipping for RPM matching. Looked like the sequence was all hard front wheel braking and getting back down into low gear with no focus on engine braking. They showed a few close ups of Rossi's throttle hand and that was interesting to watch. He's a full four fingers guy, hard and fast. His throttle looks to have very little rotation to it, like 1/8th of a turn of maybe even less. I think there was some very subtle throttle work going on there that was not easily seen. I'd love to see some on board cameras that showed the foot and hand work better. Jack | ||
| 12r |
...didn't seem to be much visible throttle blipping for RPM matching. The ECM and slipper clutch mean that they don't have to on downshifts. The M1 twistgrip has a direct connection to two of the throttle bodies and the other two are controlled by the ECM taking into account a whole raft of feedback from other parts of the motorcycle. In 04 Rossi used to downshift with the throttle slightly open to eliminate the power-off/power-on transition but since 05 it's not necessary. These guys are way ahead of us  | ||
| Jimidan |
I agree that a slipper clutch is not needed on street Buells because of the heavy flywheel limits the engine braking effect. Now the XBRR has a very small flywheel that may cause more problems with it. I have a Bucci slipper on my 998 Duck that has 3 disadvantages: it is very expensive initially ($1,200 +), it is very expensive to change the clutch pack ($350+)and it wears out relatively quickly. But on a race bike with a very light flywheel, it does significantly reduce the engine braking. jimidan | ||
| Roadsurfr |
Part of the thrill of riding my Buell is the rumble on deceleration.  | ||
| Rocketman |
I ride for miles in the twisties without changing out of third or fourth gear. Ride that Buell hard into a tight corner at speed and need to change down fast then get back on the gas quick and you'll soon see why slipper clutches work. Some of us like to ride in exactly the manner I've described. Jimidan, you have it arse about face. An engine with light reciprocating parts will offer less engine braking than an engine with heavier reciprocating parts, all things being equal. If you shift down at higher rpm on your Buell it's more likely you will slow down quicker than doing the same on most IL 4's. You'll probably find your Buells brakes will last longer too As said already, a 'back torque limiter' or 'slipper clutch' is about blending rear wheel speed with engine speed when down shifting in certain scenarios. Rocket | ||
| Bomber |
actually, you've already got a slipper clutch -- it's called your left hand -- the need for a slipper clutch is what used to be called "sloppy downshifting," but technology is great, innit? | ||
| M1combat |
"Jimidan, you have it arse about face. " Sorry Rocket  ... You have it backwards. An IL4-600 has a good deal more engine braking than an XB12 or XB9. The flywheel inertia helps to overcome the compression ratio. A light flywheel will have less inertia to be used to compress the cyl. What does compress the cyl in an IL4 then? Some flywheel inertia, the other piston's power strokes and the rear wheel . The Buell runs at 10:1 as opposed to a modern IL4's ?14:1? as well. This is why a heavier flywheel will help with peak HP too. That said... You lighten the flywheel (ala RR) and crank up the pressure... Yeah, a big bore V2 will have plenty of engine brakes and will require a slipper. An XB with stock flywheel and stock compression however, has about the same engine brakes as a 250 2-smoker. Next to none. That said.... I think I can see why you said that... When you initially let the clutch out, an engine with a heavier reciprocating mass will take more energy to spin up... That's not the classic definition of engine braking though. Engine braking happens after you've let the clutch out. Before that, it's clutch braking. So... to re-cap ... An IL4 has a lot more engine braking  . | ||
| Panic |
light reciprocating parts I think you mean rotating parts? Reciprocating part weight doesn't affect inertia, since they come to a complete stop, twice, every revolution. | ||
| Blake |
A slipper clutch is merely a one-way torque limiter. That's all. When decelerating the rear wheel back-drives the engine. This requires torque. Said torque is generated through decelerative forces and input to the drivetrain via rear wheel. When the torque transmitted from rear wheel, reduced by final drive ratio and transmission ratio, to clutch exceeds a certain value the mechanical drivetrain pathway at the clutch is severed, thus allowing the rear wheel to continue spinning absent resistance from back-driving the engine. Once drivetrain angular speeds equalize between input and output sides of the clutch or when the engine begins to drive the rear wheel instead of vice versa, the clutch re-engages. Zat make sense? Rocket, you got it backwards amigo. | ||
| Blake |
Most cordless drills have an adjustable torque limiter. They work the same in forward or reverse. A slipper clutch is exactly the same except it only works in reverse, when the rear wheel is backdriving the engine. How's zat? | ||
| M1combat |
"I think you mean rotating parts? " Err... Yeah . | ||
| Bob_thompson |
Blake, is this system at all like a sprag clutch thats been around a long time and uses ball bearings to transmit torque in only one direction or a completely different system. Also, thanks everyone for some very knowledgeable information. Bob | ||
| Diablobrian |
Yep, kinda like the ratchet in your toolbox, except a lot more heavy duty. | ||
| Patrickh |
a slipper generally works with a series of ball bearings which "roll" up a series of fluted ramps on the inside (transmission side) of the clutch basket. anyone who has ever "banged down" a couple of gears to prepare for a rapid corner exit knows how effective a slipper clutch can be. | ||
| Rocketman |
Reciprocating - because it refers to all the moving parts. Rotating is not what a conrod or piston does. YOU GUYS CAN'T READ. Jimidan said a slipper clutch is not needed on street Buells because of the heavy flywheel limits the engine braking effect. Take two identical Buells except one has lighter flywheels than the other. Which will slow down quicker under engine braking? The one with heavier flywheels because the engines power is sapped by the force needed to turn the extra weight. So like I said, An engine with light reciprocating parts will offer less engine braking than an engine with heavier reciprocating parts, all things being equal. ALL THINGS BEING EQUAL, take two identical IL 4's, except one has lighter flywheels than the other. Which will slow down quicker under engine braking? The one with lighter flywheels will decrease in speed slower because the pressure in the cylinder is identical to the pressure in the cylinder of the motor with the heavier flywheels. It is easier for the motor with the lighter flywheels to continue rotating as there is less weight to turn, so that bike will run on for longer. Now before we get into debating which came first, the pressure or the mass, my post was simply to say a heavy flywheel does not limit engine braking, IT ENHANCES IT. Now before this runs on and on let's remember we are talking about engine braking as in an engine that is attached to a motorcycle and not one sat on a table in a lab. Think about what that slipper clutch does, and the effect on engine braking if there is no slipper clutch. Rocket | ||
| Diablobrian |
Rocket has it right. | ||
| Panic |
Err... No, he doesn't. He has it backwards. | ||
| Diablobrian |
Oops my bad, I turned it around in my head. With the lightened flywheel wheel-hop gets worse, and our race bike's crank is nothing like what the XBRR has. I'll blame lack of sleep again. | ||
| The_old_poop |
RE: "series of ball bearings which "roll" up a series of fluted ramps on the inside (transmission side) of the clutch basket." They are called sprags and are most commonly used in automatic transmissions. | ||
| Jimidan |
Rocketman sez: "YOU GUYS CAN'T READ. Jimidan said a slipper clutch is not needed on street Buells because of the heavy flywheel limits the engine braking effect. Take two identical Buells except one has lighter flywheels than the other. Which will slow down quicker under engine braking? The one with heavier flywheels because the engines power is sapped by the force needed to turn the extra weight. So like I said, An engine with light reciprocating parts will offer less engine braking than an engine with heavier reciprocating parts, all things being equal." Rocket, I think we are reading it correctly, but I think you are confusing how fast an engine will rev up vs. engine braking. The lighter "rotating" (reciprocating parts go back and forth, like pistons, rods, etc.) parts will allow an engine to rev up more quickly but they also allow the forces exerted by the pistons, valve springs and combustion chamber (compression) to slow the bike down faster. Light flywheels allow for the engine to turn up rpms faster under heavy acceleration. Heavier flywheels give the engine more torque though, so it is all about compromise...as are so many other aspects of engine design. When you are off the gas, the engine is no longer pulling and in fact, is braking because of the compression, valve springs, friction, etc.. A large flywheel will not slow down as fast (inertia) as the rest of the rotating components want to, so it will continue to spin and in effect, drive the engine forward even though no gas/oxy is being fed to it to produce power. The heavier this flywheel is, the more drive it exerts under this condition. When I want to slow my big Buell down in a hurry, I pull the clutch too, because I can feel the flywheel's inertia pushing me and the bike forward. It is a plain as night and day...but you must understand the basic concept of inertia first. jimidan | ||
| M1combat |
Yep... a heavier flywheel will allow the bike to roll further or have less engine brakes. | ||
| Jimidan |
Regarding slipper clutches, it is basically like Blake and others have said, but I will give you another analogy that may help. Think of the ramped ball bearing mechanism in your clutch, that has ball bearings that separate the two halves and disengage the clutch when spun backwards (when you pull the clutch lever in). That is basically the way some slipper clutches work. Under deceleration, the back torque exerted through the wheel, to the chain, to the tranny, and then to the clutch, spins the ramped bearings backwards to force the clutch plates apart, thus breaking the drive line. When deceleration stops, the ramps rotate forward and the plates are reconnected to reconnect the drive line. This is oversimplified, but it may give you the mental image. jimidan (Message edited by jimidan on March 28, 2006) | ||
| Steve_a |
Heavy flywheels definitely give less engine braking, contrary to folklore. I tested a bunch of bikes for engine braking several years ago (article in Cycle World) and the lowest was an RD400 (two-stroke) closely followed by a Harley Twin Cam. The Buell XB had the least among sport bikes, a Yamaha R1 the most, almost to the point of locking up the rear wheel on a sudden throttle snap-off near redline in 1st, even without leaning over . . . little wonder that the LE version of the R1 has a slipper. | ||
| Bob_thompson |
Thanks much guys but as a final discussion point; I always wanted to slow for a corner somewhat with engine braking and then use front brakes mostly as in dirt track where sometimes you don't even have brakes. These slipper clutches as I see it allows "free wheeling" to speak of with no engine braking or slowing. This system would seem to be mostly for racing as brake pads and other components would wear quite rapidly although it would seem as you would be able to go much deeper and faster into a corner and just brake harder at the last moment without chattering the rear wheel. 12r also brought up a good point about not having to match engine speed to downshift. Is this essentially what we're talking about for racing? Thanks again for all the fine input. Bob (Message edited by bob_thompson on March 28, 2006) | ||
| Blake |
Bob, They are very similar; you got it! Sean, "Which will slow down quicker under engine braking? The one with heavier flywheels because the engines power is sapped by the force needed to turn the extra weight." Exactly the opposite amigo. What engine power? It is idling? Imagine a giant flywheel, 100' in diameter and made of solid steel. Imagine it is spinning at 1 rpm. Imagine trying to stop it. Now imagine a child's pinwheel spinning at 100 rpm. Imagine trying to touch it without immediately stopping it from spinning. Thinks in motion, including spinning motion, tend to stay in motion. Big flywheels keep the engine cranking longer. Remove the flywheel and the engine will stop very quickly. Meaning it will exert a LOT more engine braking upon the drivetrain. |
