Shane661
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posted February 17, 2010 10:22 AM
 Edited By: Shane661 on 17 Feb 2010 18:28
- Flywheel Lightening? -
I recall that some 12R's had a lightweight flywheel compared to other models.
Is there a big advantage to this? What purpose, outside of charging, does the flywheel serve?
Is it worth lightening one up? I seem to recall that some roadracing bikes had very light flywheels.
Shane
  
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woppi
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posted February 17, 2010 10:31 AM
Edited By: woppi on 17 Feb 2010 18:31
if i remember right:
the A model has a lighter crank + a biger flywheel
the B model has a lighter flywheel + a biger crank
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woppi
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posted February 17, 2010 10:35 AM
Left - A modell
Right - B modell
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osti33
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posted February 17, 2010 02:41 PM
Edited By: osti33 on 17 Feb 2010 22:42
Shane,
Your 12 is a "B" model right? If so it should already have the lighter flywheel on it.
A lighter flywheel might make it rev a little quicker.
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shiphteey
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posted February 17, 2010 02:56 PM
Hmmm. I thought the B models were easier to launch at the strip because of a heavier flywheel...is it the overall crank assembly then WITH the flywheel and everything bolted up to it? A models just feel a little touchier.
A.
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WARBIRD
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posted February 17, 2010 03:07 PM
+1 The A model has the lighter flywheel. Woppi.......you sure you got your photo's correct?
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NOX
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posted February 17, 2010 03:22 PM
A Model has the lighter crank.
B Model has the lighter flywheel.
They can be matched together. They take different pullers.
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Shane661
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posted February 17, 2010 03:45 PM
quote:
Shane,
Your 12 is a "B" model right? If so it should already have the lighter flywheel on it.
A lighter flywheel might make it rev a little quicker.
The 12 revs pretty darn quickly (B model, but with crank work). I was just talking in general terms. The flywheel of the 14 is actually pretty light at 2.5 lbs. What do the 12 flywheels weigh??
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Y2KZX12R
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posted February 17, 2010 03:55 PM
Shane, in general a lighter rotating mass will rev quicker. So for drag racing it will go threw the gears quicker.
But the heavier mass stores more kinetic energy so you can use that extra energy to help get the bike out of the hole.
So ideally you want a heavy crank off the line and a light crank once the clutch is out and the rpms start to rise again.
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Shane661
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posted February 17, 2010 03:59 PM
I'm mostly focused on the dragstrip with the 14, so the stock setup is probably pretty good for my needs. 
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2000redrocket
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posted February 17, 2010 08:26 PM
i would go for the heavier than the lighter. we put 16oz weights on our dirtbikes for a reason. and a local dumbass took the stock flywheel off his no torque 302 and put a aluminum 12lb flywheel on it. he could bairly pull out. said have to rev it much harder.
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NOX
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posted February 18, 2010 06:35 AM
quote:
Shane, in general a lighter rotating mass will rev quicker. So for drag racing it will go threw the gears quicker.
But the heavier mass stores more kinetic energy so you can use that extra energy to help get the bike out of the hole.
So ideally you want a heavy crank off the line and a light crank once the clutch is out and the rpms start to rise again.
If you have a light crank set up, clutch tune up on the starting line becomes more touchy........, ie, the window of a very good smooth tune up, gets smaller.......
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whitehendrix
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posted February 18, 2010 07:18 PM
the only advantage would be less parasitic loss and thus lighter rotating mass/ quicker revs. tho it will cost you in torque.
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tcchin
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posted February 18, 2010 08:18 PM
Do flywheels create parasitic losses? I thought parasitic losses were non-recoverable, like friction, whereas the kinetic energy stored in a flywheel is recoverable. Also, flywheels do not add torque, per se, although they do help control its output. Whitey: What is the electrical analogue for inertia - inductance? That's what a flywheel does in a mechanical system.
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gilberjj
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posted February 19, 2010 12:01 PM
quote:
Do flywheels create parasitic losses? I thought parasitic losses were non-recoverable, like friction, whereas the kinetic energy stored in a flywheel is recoverable. Also, flywheels do not add torque, per se, although they do help control its output. Whitey: What is the electrical analogue for inertia - inductance? That's what a flywheel does in a mechanical system.
That also is my understanding. You won't lose torque with a heavier flywheel, but it will take more energy to get it spinning right?
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almost_les
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posted February 19, 2010 12:34 PM
the additional "torque" from is just shock load from the momentum. the engine isn't any stronger, but has the ability to store energy that can be released in a short burst. great for busting out burnouts, and clutching up wheelies, not so great for 1/4 mile mph. your clutch setup (and riding skill) would dictate whether a light or heavy crank would be better.
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NOX
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posted February 19, 2010 04:26 PM
If you have a crappy clutch set up, or a bad clutch hand, the heavy crank will help.
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KZScott
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posted February 19, 2010 04:28 PM
and you run the light crank and light flywheel right?
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whitehendrix
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posted February 19, 2010 09:37 PM
quote:
Do flywheels create parasitic losses? I thought parasitic losses were non-recoverable, like friction, whereas the kinetic energy stored in a flywheel is recoverable. Also, flywheels do not add torque, per se, although they do help control its output. Whitey: What is the electrical analogue for inertia - inductance? That's what a flywheel does in a mechanical system.[/quote
Tim, at the risk of looking like a retard (mainly since you have a 300+ I.Q. and validating a point to an engineer is worthless,, lol) i will say "yes"
i say this because tho the "flywheel" is sort of that.. a flywheel, it is more of a rotor to hold the magnets to generate power, and just being heavy is kind of a bonus of design and application.
by parasitic loss i meant to accelerate rotational speed, a heavier flywheel would take more mechanical input thus translating into more time taken to get from base X RPM to target X RPM.
i mean, i am no mechanical engineer by any stretch, so please, correct me if my assumption in this is incorrect!! i'm always willing to see what you have to say.
as always tho, i see you point and accept, since theres no arguing with you. :P
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tcchin
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posted February 20, 2010 12:07 AM
Edited By: tcchin on 20 Feb 2010 08:10
Losses are an irreversible conversion of energy from one form to another, like motion to heat in the case of friction. Inertial forces are not losses, as the energy required to accelerate the flywheel is stored in the mass of the flywheel, and is easily recoverable (it's not lost). It's the whole Newton's First Law thing: a flywheel will resist a change to its energy state by resisting both acceleration and deceleration.
Most bikes these days combine the alternator's permanent magnets with the engine's flywheel into a single multi-functional unit. On the Suzuki kit alternators, the positions of the stator and rotor are reversed, with the stator surrounding the rotor, instead of the rotor surrounding the stator. This configuration reduces the inertia and radius of gyration of the rotor considerably and limits the influence of the rotor on the engine's ability to accelerate or decelerate. The engine still produces the same amount of torque, but the lower rotating mass means that the engine will accelerate more quickly.
BTW, this is why inertial dynos are less accurate in terms of estimating absolute power output, but that's a whole 'nother story.
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whitehendrix
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posted February 20, 2010 09:28 PM
as always, it's a pleasure to read the tech talk of someone whos forgotten more than i'll ever learn. lol
i understand that a flywheel stores inertia and the variance in losses.. i was just under the impression that in order to spin a heavier flywheel, it would require more mechanical input.
basically that, if one were to have a motor, that motor would be timed to spin from 1000rpm to 9500 rpm.. it would take less time (and assuming less power?) to spin from 1000 to 9500 with a light flywheel than a heavy one.
i was also thinking that, tho the lighter flywheel would take less power to spin up, it would in turn offer less torque (less weight there to offer torque?)
im no physics expert, but thats what i was thinking.. am i way off base with this? i don't want to think i am right on something and actually not be!
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Y2KZX12R
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posted February 21, 2010 05:42 AM
Edited By: Y2KZX12R on 21 Feb 2010 13:45
Think of it this way. the Hubble telescope is weightless in space orbiting the earth right?
But it still has mass. So if its not moving relative to your position standing (floating) next to it has no kinetic energy in relation to your position standing next to it.
Now you push it with your hand and it starts to move very very slowly say 1 inch per second, not very fast, but if your hand was between it and the space shuttle your hand would be crushed because its mass is 16,000 pounds and its in motion. Its retained the stored kinetic energy that you put into it when you pushed it.
This is why weight and mass are not the same. And also why communication satellites spin like your crankshaft, it provides stability, yet they are weightless. A satellite will spin for years and years and years unless something absorbs some of the kennetic energy it has. Which the earth does do, very, very, very, slowly.
Now to really confuse you, now think of the Hubble it self on a bigger scale and its relationship to the earth. The Hubble is rotating around the earth at some 17,000 - 22,000 mph relevant to the earth. (I don't know the actual velocity, depends on the orbit) So it has stored kennetic energy in it even before you pushed it with your hand standing next to it. And LOTS of it !!!! But kennetic energy can be stored on many axis. So you could have a spinning satellite with kennetic energy stored on its spinning center-line and then it could be tumbling at the same time on another axis and then it could be moving away from you all while is moving around the earth. So thats 4 different axis that it has stored kennetic energy in.
Back to motorcycle crankshafts.... so the crank mass also offers another desirable or undesirable action. it offers stability just like the spinning communications satellite. It will resist changes to its rotational axis. this is what makes it more stable at speed and also harder to lean the bike over at 11,000 rpm than at 1000 rpm. The wheels also do the same thing. This is why a bicycle is stable while riding it but not if you sit on it stationary.
Ever ride a motorcycle with carbon fiber wheels at very slow speeds, like in crawling traffic? Its strange and you may feel like the bike is tipsy because it is. 
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Shane661
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posted February 21, 2010 08:00 AM
Edited By: Shane661 on 21 Feb 2010 16:14
So...
Why does one 12R have a heavy crank and light flywheel...vs. a light crank and heavy flywheel?
What if you had a real heavy crankshaft...but no flywheel at all? Or a super light crank, with a really heavy flywheel? Will they all act the same?
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tcchin
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posted February 21, 2010 08:21 AM
Edited By: tcchin on 21 Feb 2010 16:22
quote:
i understand that a flywheel stores inertia and the variance in losses.. i was just under the impression that in order to spin a heavier flywheel, it would require more mechanical input.
A flywheel has inertia, which it adds to the crankshaft's inertia. The formula you're referencing is T=Ixa where T is torque, I is inertia and a is angular acceleration. Note that this is a cross-product and all of the terms are vectors.
quote:
basically that, if one were to have a motor, that motor would be timed to spin from 1000rpm to 9500 rpm.. it would take less time (and assuming less power?) to spin from 1000 to 9500 with a light flywheel than a heavy one.
i was also thinking that, tho the lighter flywheel would take less power to spin up, it would in turn offer less torque (less weight there to offer torque?)
Yes, since angular kinetic energy is (Iw^^2)/2 (I is inertia, w is angular velocity) and power is the time rate of change of energy, it takes more power to achieve the same angular velocity if you increase the system's inertia.
And no, a lighter flywheel does not offer less torque. Torque is Fxd where F is force and d is the radial distance at which it's applied, and is kind of a static property. It's not until you multiply it by an angular velocity (like RPM) that it becomes power. What a flywheel will do is provide you with kind of an angular momentum Bondo, so if you bog your motor and your engine speed starts to drop, the flywheel will resist the change in energy state (Iw^^2)/2, smoothing out the launch. Does this "offer" or produce torque? Technically, no, it just transfers kinetic energy that's stored in the flywheel to the crankshaft.
Back to my comment about dynos, a Factory Pro dyno measures force applied to a load cell in the dyno chassis when the engine is at a steady-state RPM. This force is used to calculate torque, which is used to calculate power. These are all direct calculations. An inertial dyno measures changes in angular momentum in a spinning drum of known inertia to derive power (time rate of change of momentum). If you are able to log RPM and map it to the changes in angular momentum, you can calculate torque. The problem is, the bike's inertial properties are unknown. If you change the inertia of the bike's drivetrain by changing wheels or tires, or if you change gearing and don't log RPM, then the dyno will give you different results even if the motor is producing the same amount of power. This is because the inertial change caused the drum to accelerate at a different rate, which yielded a different power reading.
The same principles apply to flywheels. A lighter one will allow your engine to rev more quickly, even though the engine is producing the same amount of torque. And as Jim said, there are other benefits to having drivetrain inertia. Having too little might make the bike difficult to ride and control. It's all a balancing act.
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tcchin
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posted February 21, 2010 08:37 AM
quote:
Why does one 12R have a heavy crank and light flywheel...vs. a light crank and heavy flywheel?
What if you had a real heavy crankshaft...but no flywheel at all? Or a super light crank, with a really heavy flywheel? Will they all act the same?
The most likely answer is probably related to money. KHI was probably able to buy a smaller rotor at a lower cost, so they changed the crankshaft to compensate for the reduced flywheel inertia.
However, crankshaft design is a very involved process with many dynamic (mechanical, hydro, aero) and metallurgical considerations. For example, changing crankshaft mass changes the way the crank will vibrate linearly and torsionally, which affects dozens of other aspects of the engine design. Everything has to work together to make an engine perform adequately and last a reasonable amount of time. So it's not just the total inertia of the crankshaft system that's important, it's also stiffness and the distribution of the mass that's important. Just like balancing tires, it doesn't matter where you put the weight along the width dimension of the tire during a static balance, but when the wheel starts to spin, and the forces become dynamic, and you start to see out-of-plane shaking, then the weight placement in the third dimension becomes important.
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