| Author |
Message |
    
Rocketman
| | Posted on Tuesday, March 28, 2006 - 07:27 pm: | 
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Ok, I hear what you guys are saying and I'm feeling a little stupid here, but I can't see that 100' flywheel spinning for long when the forces feeding back into the crank on overrun (which is not tickover Blake) from the rear wheel are trying to push it around. That's a lot of mass to rotate from the rear wheel hence the bike slows down quicker because the rear wheel doesn't exert enough force to turn the mass involved so the rear wheel slows. A pinwheel offers little resistance to the rear wheel on overrun therefore I see the rear wheel spinning that assembly rather than it slowing the bike down. And isn't this why we need slipper clutches?
Well if you guys are right I've learned something new, but I need to see the math to understand it.
Rocket |
Roadsurfr
| | Posted on Wednesday, March 29, 2006 - 12:48 am: |
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Some time ago one of the motorcycle mags did a performance comparison of various bikes. They were astounded to find that the big twins actually produced LESS enginebraking than IL4s. I was surprized too. |
Rocketman
| | Posted on Wednesday, March 29, 2006 - 04:33 am: |
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Ok, I finally got my head around this. The crank is an energy storing device, so I imagined a big steam engine that 'ran out of steam' so to speak, but the crank is huge so it kept on turning and turning and turning and turning, then the fire got stoked, and it turned some more and some more and some more, until it ran out of steam, and it still kept on turning and turning and turning and turning, all over again.
Now I put that big steam crank in my Buell last night, yes it was a challenge, and I went for a burn. This is what surprised me. Because the crank was so heavy it thus stored a LOT of energy, so when I decelerated in gear the crank kept on spinning, assisted by the push on overrun from the rear wheel, and my big Buell kept on rollin and rollin and rollin and rollin.
Man, in all my years, I feel like a complete asshat.
All I can say in my defense is, I've spent most of my growed up life riding on dem dare big twins, and they must have a lot of cylinder pressure. More so my Buell because when I shut off I damn near go over the bars. Now my mates old CBR600 for example, had no engine braking to speak of, and nor did the last Fireblade or R1 I rode too. Ok, they were older models, so what's all that about? But is this too the source of my confusion. Anyway, I finally got my head around it and thanks for helping to educate me. One learns summat new every day.
Rocket |
Rocketman
| | Posted on Wednesday, March 29, 2006 - 04:45 am: |
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I forgot to mention, another good analogy a friend helped me with to get my head around the crank thing was sound effects.
He did dog noises. Rar rar, rar rar, rar rar, was a race engine with very light crank. You rev it up from tickover, blipping the throttle, and it damn near comes to an instant stop on overrun, rather like an F1 engine if you like.
Raaar raaar raaar, raaar raaar raaar was an un tuned family saloon type with a big heavy crank..........you get the picture.
Now why couldn't you lot do dog noises, than there'd have been no confusion LOL
Rocket |
Newfie_buell
| | Posted on Wednesday, March 29, 2006 - 10:18 am: |
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A friend of mine from the "Isle of Wight" that rides a Speed Triple lived here for a couple years and commented on the S1.
"That thing got a lighter flywheel than a sportster", He was surprised at how it could decelerate quicker/faster.
I would think that with a heavier flywheel it takes more power to spin it up therefore slower spool up speeds and spool down speeds. With the lighter flywheel it spools up (revs) quicker and spools down quicker as well.
Excellent Lesson in Momentum Fellas!!!!!! |
Panic
| | Posted on Wednesday, March 29, 2006 - 07:33 pm: |
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How to have more engine braking with heavy flywheels:
1. pull the clutch in
2. wait 3 seconds
3. don't touch the throttle
4. release the clutch
5. bringing the wheels up to speed drags the bike down |
Blake
| | Posted on Wednesday, March 29, 2006 - 08:48 pm: |
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That is flywheel braking, not engine braking. ![: ]](http://www.badweatherbikers.com/buell/clipart/proud.gif) |
Panic
| | Posted on Thursday, March 30, 2006 - 09:52 am: |
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By that definition flywheel inertia does not affect "engine braking". |
Blake
| | Posted on Thursday, March 30, 2006 - 06:37 pm: |
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Okay then, it's "clutch" braking, not engine braking.
You do realize I'm kidding with you right? |
M1combat
| | Posted on Thursday, March 30, 2006 - 06:48 pm: |
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What's the primary force in engine braking? Compression ratio yes? And that's got something to do with RPM as well yes?
With an IL4 you're compressing a 14:1 chamber, and about 2-3X as often as with a 6800RPM 10:1 Buell. The flywheel's inertia helps you to overcome the part where you're compressing the cyl.
I still say they should ban slipper clutches... They should go to pattern shifters in F1 too... with a damn clutch. |
Jackbequick
| | Posted on Thursday, March 30, 2006 - 08:53 pm: |
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And the NHRA needs to ban wheelie bars on everything, cars and bikes. And find out who can drive and who can't.
Jack |
Steveshakeshaft
| | Posted on Friday, March 31, 2006 - 03:32 am: |
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M1Combat, you have to figure that a petrol engine is a variable compression engine. This is due to the throttling effect of the butterfly in the inlet tract. (Contrast this with a Diesel engine, not throttled). With a closed butterfly the pressure drop from atmospheric will be significant so you will not have a "true" 10:1 compression ratio in the motor under closed throttle engine braking conditions. Therefore, the throttle butterfly has a not insignificant effect on engine braking. |
Cowboy
| | Posted on Friday, March 31, 2006 - 05:43 am: |
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Lord I need both feet and both hands now.Are we going to have to get a JAKE(brake) now. |
Jackbequick
| | Posted on Friday, March 31, 2006 - 07:21 am: |
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Get a jake with an automatic mode. Any time you close the throttle it activates the jake.
It is the best way to get the fast shifts on a jake equipped diesel. You can progress steadily up through the gears even on a steep climb.
Jack |
Blake
| | Posted on Friday, March 31, 2006 - 08:01 am: |
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What Steve said. 
Plus some bloviating from Blake... Like Steve so astutely states, engine braking is mostly a result of the vacuum pulled during the intake stroke with the throttle closed, and frictional losses. Like Don said, CR, engine speed, and flywheel inertia are major factors affecting how strong the engine braking effect will be.
A high revving small flywheeled IL4 has more engine braking than a big flywheeled V-Twin. Steve Anderson proved it in an excellent article in Cycle World not too long ago. Conventional wisdom turned out to be wrong. Kinda cool when that happens I think. |
Steveshakeshaft
| | Posted on Friday, March 31, 2006 - 08:50 am: |
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What Blake said.  |
Rocketman
| | Posted on Friday, March 31, 2006 - 12:10 pm: |
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Steve Anderson proved it in an excellent article in Cycle World not too long ago.
I'd like to read that article very much. Seems it suggest from what you're saying that conventional wisdom has had me fooled for years despite my understanding of pressure forces etc.
Anyone know which copy exactly, and back copy address, thanks?
Rocket |
M1combat
| | Posted on Friday, March 31, 2006 - 02:30 pm: |
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"And the NHRA needs to ban wheelie bars on everything, cars and bikes. And find out who can drive and who can't. "
That's what I'm sayin' . |
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