| Author | Message | ||
     Baggermike |
Hey guys Pariah had I have a question to what is the proper way to down shifting with a slipper clutch, I think no throttle and just down shift and Pariah thinks we should blip the throttle like on regular bikes with out a slipper clutch, so I thought someone with more track time or racer school could shed some light on the proper way of down shifting this bike with its vacuum slipper clutch. Mike | ||
| Bigdog_tim |
Well - am not a racer (ok - have my share of track time) and not a racer schooler... But... Leaving my neighborhood is a fairly steep hill after 5 DELICIOUS curves. On my Firebolt, often (ok - most days) the tires would chirp and be squirrelly coming down the hill after the last curve - throttle, no throttle - would always be squirrely. On the 1125R - no throttle - no squirrelly. On the throttle - no squirrelly. Not an OFFICIAL response - but I suspect no throttle. I could be wrong (and often am) - but I get more traction and positive response with no throttle in the one condition every day that I use the slipper clutch. YMMV. | ||
| Interex2050 |
This all really depends on how the vacuum assist is configured; sensitivity etc... Overall though, I think it boils down to the following: The vacuum assist works using the pressure differential between some reference and a point past the butterfly valves. So in turn the higher the rpms and the quicker the throttle is closed the greater the vacuum created. Hence I believe that with a quick blip of the throttle a much higher vacuum will be achieved, hence making the slipper clutch more effective. | ||
| Zac4mac |
My thoughts - The slipper is for "race" speeds. Catch a surprise hairpin and drop 3 gears and not skitter off the road. Regular daily riding, use the clutch normally. I like sliding thru 3-6th by relaxing or bumping the throttle a tad and slipping it in clutchless. Very nice on a cold morning not having to let go of the heated grips. The engine deceleration is less than I'm used to, but I think that's the engine, not the slipper. As with any "technique", YMMV. Z | ||
| Trojan |
The whole point of a slipper clutch is to be able to downshift multiple gears without the need to 'blip' the throttle to match engine/gearbox speeds, or to have to manually slip the clutch in order to stop the rear wheel locking. Once you get used to it (and it takes some getting used to for someone used to the 'traditional' way of doing things), the technique with 'normal' ball & ramp type slipper clutches is: Barrel into a corner, pull the clutch lever in, change down however many gears you need to, let the lever out hard and the slipper clutch will stop the rear wheel locking or skipping. No need to try and slip the clutch manually or to have any mechanical sympathy at all really. It will however reduce engine braking at the same time to almost nothing, so again you have to re-educate your brain in this regard and rely more on the brakes than the motor to slow down. I haven't used the 1125R vacuum assisted clutch so can't comment on its effectiveness compared to a 'normal' ball & ramp type slipper clutch, so the technique may be slightly different ;) | ||
| Hwyranger |
After hitting the track yesterday, I found the slipper clutch does not need a blip of the throttle at all. Coming into turn 1, I was on the brakes and downshifting two gears. I had a tendency to slowly let the clutch out without blipping the throttle and it worked just fine. By the time the clutch was out, my brakes were off and I was dipping into the turn and rolling on the throttle. Towards the later sessions, (fatigue) I didn't ease out the clutch as much, and that's when I felt the effect of the slipper. It was just as if I had been feathering the clutch (as the rear wheel behaved very nicely) and I was in the turn MUCH easier and more comfortably. Not an engineer, so i couldn't tell you what was going on inside the bike, but as the rider, I don't think the blip is necessary. | ||
| Ratbuell |
Vacuum is vacuum - it's made by the pistons pulling against a closed throttle plate. Opening/closing quickly makes no difference at all in the amount of vacuum. Don't blip. The slipper disengages at something like 2% TPS reading IIRC (think I read that somewhere). | ||
| 12r |
My R1 manual advises against blipping the thottle on downshifts. If you, it disengages the slipper clutch. Depending on the severity of the downshift, the ECU modulates the engine braking to achieve sublime poise on the way into corners. As has been said above, it takes a bit of getting used to but once you've discarded years of riding habits and left mechanical sympathy at home, it's the fastest way to travel  | ||
| Buellrcr |
the slipper works off of vacuum and rpm the more the rpms are up , the more vacuum the slipper will help more on the down shifts. | ||
| Baggermike |
I think the design of the clutch working off of vacuum is a really good idea, it make the clutch lever easy to pull and allows the clutch to slip, has anyone had the Kuryaken hypercharger that worked of vacuum and would be closed at idle and open when you gave it lots of gas, same thing, I tried it out on the highway and when getting off of the highway I would downshift hard with out using the clutch lever or throttle at all, it works great and also slowed me down faster than I thought it would, I thought I read that you really do not need to use the clutch at all with this bike on the track going up or down. I just found out about a school that teaches advanced riding called ARC Advanced riding clinic and I feel that I should take this course before going to race school, it is for someone who has been riding atleast a year, I have been riding thence ? I can not remember that far back, anyway I feel I can always learn something that might save my life on the street, so I am thinking of taking this course, it cost 300.00 and you can check it out at www.totalcontroltraining.net My main concern is my son, I planed on taking him to the advanced riding school and was going to do that with him, now I am not sure what to do next but the Advance Riding Clinic sounds like it would be better for surviving the streets, and then I can teach my son what I learn. Mike | ||
| Interex2050 |
A ball/ramp slipper clutch is nice because it uses the forces that cause rear wheel chatter, to work. I believe that the vacuum assisted one is not quite as useful, as those forces are not as involved. They only come into play when the vacuum is great enough to loosen up the clutch plates; which depends on the rpm/throttle opening. I have noticed that the rpms tend to linger before they drop down... Almost like a raised idle, used to reduce engine braking.... | ||
| Ratbuell |
All I know is at Pocono burning out of the back straight at around 130-140 (I think - the speedos were taped), I'd brake and clutch together to freewheel and scrub speed (the WRONG way to do it, but I wanted to see if the bike would complain), and right before tipping into the left at around 40mph I'd knock 2 quick downshifts and dump the clutch lever. Bike never missed a beat. | ||
| Court |
I think the vacuum increases when you close the throttle. Based SOLELY on years of driving cars and trucks with vacuum driven windshield wipers. Some of you may recall . . .when you stomped on the gas pedal the wipers stopped. . . when you took your foot off . . . Wap-wap-wap. . . they went like mad. I suspect that with the throttle open the air is being supplied to the lower pressure area created when the piston retreats. When the throttle is closed the source of that air is restricted and the retreating piston [changing that old Ideal Law (P1V1T1 = P2V2T2) ] then creates a vacuum. This would seem to work well for the slipper clutch application and support the don't "blip" logic. What the heck does clutch pull have to do with this? Is there a vacuum lever assist circuity that I am unaware of? | ||
| Thurstonbuell |
Interex.....Read Court's post in the Pariah Chronicles , some good info there | ||
| Ccryder |
Court: We took this: "Wet, multi-plate, Hydraulic Vacuum Assist (HVA) Slipper Action Clutch, hydraulic clutch lever effort" to mean there was a slipper clutch with a vacuum assist at low RPM to lighten the clutch actuation. See pict below:  Neil S. | ||
| Court |
Interesting. My GUESS, from reading that, is that the motorcycle has a hydraulic clutch and that the cue to engage vaccuum assist of the slipper action comes from the use of the lever. I had misread before that someone thought the LEVER EFFORT was made lighter due to being hyrdaulically assisted. In others words . . . operating the lever causes the vacuum to ASSIST engagement of the slipper clutch, not to assist lever pull. | ||
| Interex2050 |
From what I understand Court and I are talking about the same thing... "when you stomped on the gas pedal the wipers stopped. . . when you took your foot off . . . Wap-wap-wap. . . they went like mad." This is more support to why blipping the throttle makes the the vacuum assisted slipper clutch more effective. Because by blipping the throttle you further raise the engine rpm after which you abruptly close the throttle, thus a greater vacuum. On the other hand, now that I think more about it, if one does not blip the throttle; The same thing also happens when one just "drops" the clutch at first the clutch slip is very limited but as the rpms shoot up from the clutch re-engagement the vacuum builds and limits clutch bite... I still by that by blipping the throttle you will get a smoother transition, but less engine braking. I guess blipping the throttle really boils down to if the rider wants the slipper clutch to be fully engaged before or shortly after the downshift. (Message edited by interex2050 on March 18, 2008) | ||
| Ratbuell |
Court - vacuum does both on the 1125r. If you get a chance, pull a clutch lever on a bike that's not running and feel the resistance. Then fire it up and pull it again. Buell claims something like a 30% decrease in lever effort when the engine is running. I've done the little test above - it's pretty wild. I guess (not having a full manual yet) it's a dual circuit - one circuit routes vacuum to the clutch actuator itself for a boost like power brakes in a car, and the other to the slipper mechanism. | ||
| Interex2050 |
Joe, I believe its all one line, the slipper mechanism and the clutch actuator are attached to one another. (the diaphragm and the slave cylinder) So all it does is take some of the pressure off the clutch springs, making it feel lighter. | ||
| Ratbuell |
I'll have to drive my turbo car to verify (boost/vac gauge)...but I don't think you get any higher vacuum at higher rpms than you do at lower rpms. There is a difference between idle and off-idle speeds - I think it idles at 12 in/hg and engine braking nets about 20 in/hg...but it's 20 any time the engine is braking the car. Not 20 at 2k and 25 at 4k. There is only a finite amount of vacuum that can be created by the 'pump' (piston in cylinder) against the backside of the throttle plate. The only way to get more vacuum is to use a bigger 'pump'. | ||
| Ccryder |
Court: My read is it is two-fold. It reads "assistance from the engine vacuum for smooth and light clutch effort". My take is that aids in lessening the clutch lever effort. Then the vacuum assist also producing the same effect as a slipper clutch for a ........ I just bet someone knows someone that can clear up this slippery assisted confusion. Later, Time4Lunch Neil S. | ||
| Ratbuell |
Ah. Gotcha. For the wap-wap-wipers, the reason they slow when you step on the gas is, when you open the throttle plate the cylinder is allowed to bring air into the motor which takes you to put-near 0 vacuum at full throttle (or positive pressure on a boosted vehicle). Remember back in the 70s when you could buy those goofy "fuel economy" gauges? All they were was a vacuum gauge. Open throttle plate equals no blockage between atmosphere and piston, so no vacuum ("Bad Economy"). Closed throttle plate equals blockage, and vacuum ("Good Economy" - remember back then fuel was delivered by being sucked through a carburetor, so the less air travelling through the carb, the less pull for fuel). The variance between open and closed throttle nets you a linear increase in vacuum (as you close the throttle)...but it will only increase to a certain level of vacuum as determined by the size of the 'pump' - in this case, the *displacement* of the engine - not the *speed* - versus the size of the idle circuit (engines always get *some* air or they'd stall), or intake leaks, etc. I'll leave it to Court and other smart people to figure the math out on it, though... ;) (Message edited by ratbuell on March 18, 2008) (Message edited by ratbuell on March 18, 2008) | ||
| Baggermike |
I can, it just works. | ||
| Interex2050 |
Hmm... That is an interesting point... Darn it, now I want to hook up a vacuum gauge to the slipper clutch line. But on the other hand, the intake pressures would be different on a naturally aspirated engine. And if the engine is turning faster the pistons would be displacing more air, and even though its by no means a perfect seal in there it should still yield a higher vacuum... I am really enjoying this debate. And really rather curious about its outcome. | ||
| Xl1200r |
I have a boost/vacuum guage in my car and I agree with Rat - There is really no difference in vacuum when the throttle is closed at any RPM aside from idle. My car has a supercharged engine, and at idle I think I'm around 10". With the throttle closed at speed it's closer to 18", and only starts to settle back to 10" within in a few hundred RPM of idle. I'll experiment to play around with downshifting - that is, if the vacuum increases linearly as the revs come up, or if it snaps down as soon as you let the clutch out. My guess is as soon as the throttle closes, the vacuum goes to max, maening that blipping woudln't help anything aside from leeting the clutch do less work - which isn't always a bad idea, IMO. | ||
| Ratbuell |
And if the engine is turning faster the pistons would be displacing more air, Incorrect. It is moving the same amount of air, it's just cycling through the "batches" faster. Every stroke of the engine moves the same amount of air...then an exhaust valve opens and it goes away, and a new batch moves in. All you're doing at higher rpms is cycling through the batches (still all the same size as each other) faster. | ||
| Interex2050 |
I suppose what I was trying to say was: It displaces more air per unit time For instance lets look at a over simplified single cylinder 500cc engine: this engine displaces approximately 500cc every two revolutions (assume perfect pump with an incompressible inviscid fluid) hence the average flow rate is as follows: at 1000rpm: 500*1000*1/2= 250000cc/_min or 0.14612_ft^3/_s at 6000rpm: 3000*500*1/2= 750000cc/_min or 0.4414_ft^3/_s This is much simplified, as we are not taking into account the fact that the fluid in question is compressible, we are neglecting losses, etc... But none the less there is a substantial difference. The reason flow rate plays a big part in this is because of the idler circuit; it can only let in so much air per unit time. Or more accurately the head losses involved with the idler circuit follow the relationship: k(V^2/(2g)) Thus if the air is being evacuated at a faster rate the idler circuit cannot keep up, thus theoretically yielding a higher vacuum. With a non-naturally aspirated engine, such as the turbocharged and supercharged engines above, the not only is the air being sucked by the engine but is also being forced in by the "pumps"... And the circuit associated with those is rather different, as they may have pressure release valves etc... (Message edited by interex2050 on March 18, 2008) | ||
| Spectrum |
I just finished my scuba divemaster certification. Please don't get me started doing gas physics computations again.  | ||
| Ratbuell |
Yes, but that's what the engine *braking* force is - when up against an idle circuit at higher rpms, this is what slows the engine back to idle speed. It cannot physically pull any more air into the system. The result is not increased vacuum, it is decreasing revs. You are (in effect) strangling the engine during engine braking, and its natural reaction is to decrease the rate at which it is trying to breathe in order to reach its "natural" respiration rate. The vacuum is a constant relationship between cylinder displacement and air inlet; revs do not (*can*not?) affect the pressure level. Again - you are not moving any more air per cycle (between valve openings). It's just that each cycle occupies less time. Cylinder volume is cylinder volume, and the exhaust valve still expels cylinder contents every revolution. | ||
| Baggermike |
WOW I feel like I started a fire with all the replies to this post, Anyway I thought it was a simple yes or no question, I say no blimping the throttle just stomp down on the shifter, it is a hard habit to break, like taking my two fingers of the clutch lever because I really only need it for stopping, but habit again and just does not feel right not having my two fingers on both levers. Mike |
