Changing the flywheel

[Toast]

Hey all, just wondering if anyone's had any experience with changing their flywheel to a lighter one?

My 02 6r revs a lot slower than my mate's 04, and I reckon it's at least partly 'cos of the flywheel.

Would changing it make the connection between wrist and rear wheel feel more direct? Too direct maybe?

[XTC]

Whats an 02 6R?

[she_said]

Whats an 02 6R?

im guessing zx6r

[WINJA]

Hey all, just wondering if anyone's had any experience with changing their flywheel to a lighter one?

My 02 6r revs a lot slower than my mate's 04, and I reckon it's at least partly 'cos of the flywheel.

Would changing it make the connection between wrist and rear wheel feel more direct? Too direct maybe?

I TOOK MY FLYWHEEL OFF FOR A FEW DAYS AND THE BIKE FELT LIKE A ROCKET , BUT THE BATTERY KEPT GOING FLAT.ITS MORE THAN JUST A FLYWHEEL THAT DICTATES RESPONSIVENESS. HOW DO THE BIKES COMPARE IN A DRAG RACE

[Toast]

Yeah, sorry, '02 6R = 2002 Kawasaki ZX-6R.

In a drag race...well, with equal riders, the 20kg lighter and 8hp more powerful would smoke I suspect...the thing that gets me wondering is that when you blip the throttle on the '04 the revs rise and fall really rapidly, and when riding it, it's really easy to get the power on, and feels great.

Why would taking the flywheel off cause the battery to go flat WINJA? Does the battery charge off of it?

I think I read somewhere that drag racers take them off and gain a second down the quarter...? True or BS?

[Brian d marge]

By removing the flywheel , you will make the bike feel ( for a want of a better word ..more peeky)
ie the rotational speed changes of the crank will be felt more ..it will rev quicker .. not more , or produce more power
But a low Rpm the engine will be more difficult to handle ,,,ie sort of Snatchy

this is be cause a flywheel stores energy , same as a battery ( take theflywheel off a chainsaw and you cant start the thing,, this is because there isnt enough energy in the crank to get it past tdc and compression ,,,add some stored energy and it will sail through ..the chemicals ( gasoline ) releasing more to the flywheel which is stored for the next compression stroke

By removing the flywheel you are only saving a few kg ,,( the alternator is in there and charges the battery ..) so the negatives out weigh the positives ...

As a matter of fact on my MX bike, I move the effective radius of the flywheel out so that more energy is stored making the bike easier to control in the tight stuff ( the wieght gained was minimal as I only moved the outer radius ,,the metal in the middle doesnt do much st is there only to support the rim ...so it can be made very light ......)

Stephen

[sAsLEX]

As a matter of fact on my MX bike, I move the effective radius of the flywheel out so that more energy is stored making the bike easier to control in the tight stuff ( the wieght gained was minimal as I only moved the outer radius ,,the metal in the middle doesnt do much st is there only to support the rim ...so it can be made very light ......)

Stephen

it is linked to rotational inertia, ie something spinning is hard to stop spinning etc, and this has a multiplier in it related to the distribution of mass across the spinning thing. A disc with all the weight at the edge has a factor of 1, where one with the mass equally spread from the centre to the rim has a factor of 0.5. So a solid disc has half the inertia of an ideal ring with the weight at the rim.

[Brian d marge]

it is linked to rotational inertia, ie something spinning is hard to stop spinning etc, and this has a multiplier in it related to the distribution of mass across the spinning thing. A disc with all the weight at the edge has a factor of 1, where one with the mass equally spread from the centre to the rim has a factor of 0.5. So a solid disc has half the inertia of an ideal ring with the weight at the rim.

Yup
not sure about the multiplier
But the formula is something like Inertia = M K^2 where k is sqrt ( I/A) where I is the polar moment of Gyration ( pi x r /64) ...or sumthing like that ,.... not reaching over to check
Basically you can increase the mass or u can move the radius at which the effective mass of the flywheel rotates out ...look at the old motor guzzi falcone out board flywheels for a good example large THIN and light ,,( bloody awful looking)
or any diesel engine ,,,.... so yes as u said a solid disk has less storage of energy than a thin ring which is how I did my MX bike ,,,,,,

Stephen

[FROSTY:Me]

I'd suggest theres a whole bunch of other stuff affecting how crisply the two bikes rev. The first that springs to mind is re the fuel injection vs carbs
crank angle etc etc.
If you both had bikes the same age then the answer is within your riding etc.

[Motu]

The flywheel is the most important componant in an engine as far as how it effects performance,and yet it doesn't change the HP at all.Take the most radicaly tuned engine you can find,an F1 motor say,it won't idle below 5000rpm,hard to start and revs like flicking a switch - put a 3ft cast iron flywheel on it and it will idle like a Model T and start by hand.Take the flywheel off a tractor engine and you will no longer be able to hand crank it,it won't idle and throttle response will be like a racing engine.The flywheel has more to do with engine characteristics then anything else you do to it.

The flywheel is most important of all on a trials bike,it's the flywheel that makes the bike do what it does...even on a modern quick reving trials bike - the flywheel stores energy,before the trials rider launches he revs the shit out of it,putting energy into the FW,then he releases the energy,it's stored and can be tapped at will.MX and Enduro riders use FW weight to change how their bike responds - a classic example is coming out of a corner with some ''traction variables''...a light FW bike when hitting a soft spot or hole will rev up quickly,stepping the bike out,then when it gets traction again the revs come straight back and the bike snaps back inline - a heavier FW bike will rev up slower and keep the spin going,making a smoother transition.Apllies equaly to road bikes if you ride to that level...that's the advantage the Dukes had over 4s in WSB years ago.

But a heavier FW will make it harder to turn the bike,the gyroscopic force resists a change in direction.This is important in MX,and choosing a flywheel is almost as important as tyre or gearing choices.In US Flattrack racing in the early 70s,the competion was between the XR750 Harleys,which had twin flywheels and single crankpin like a single,the British twins like the Triumphs,these were a parralel twin with a centre FW,and the Yamaha XS twins,these had a bottom end like 2 singles together,4 flywheels and a long crank.The XS Yamaha was compromised because it need heavier FWs,but because the weight was further out the bike became hard to turn.

As Frosty says there is a lot more to how your bike performs than just the flywheel,changing FW weight is fine tuning on a top tier level,and for what it's worth my preference is for more weight.

[Brian d marge]

But a heavier FW will make it harder to turn the bike,the gyroscopic force resists a change in direction.This is important in MX,and choosing a flywheel is almost as important as tyre or gearing choices.In US Flattrack racing in the e.
.

Thats what I said ...cept Motu s was a more interesting read,,,,Yes I Like Enduro ..as I am crap at MX ..( unfit and me balls are 2 small ) ...So I went for a weld on weight ..At the max radius I could get ,,, ( the mass ended up rotating round a 75mm rad
Our Local track is tight and twisty so I wanted ( as was said , traction off the bottom) especially one corner where there is a small Jump ,,,I need it to stay planted as if spin I cant get the drive of the jump and it loses me a lot of places ....
Also at the end of a Long Enduro I am v tired and cant keep throttle open So I need the lugging low down traction to maintain a average pace ......

Stephen
Dont get me started on fuel injection ...love the thing great Idea......

[Toast]

Hey Motu, when you say the Dukes had the advantage...did they have the lighter flywheels or the heavier ones vs. the 4's? Do twins commonly have different weight flywheels to 4's?

[Motu]

A bit more complicated than that,but a V twin typicaly has a heavier crank layout than a 4,different power impulses and a falling torque curve,I was oversimplifying.