From: couyant@rox.mel.dbe.CSIRO.AU (George Couyant Convex Support)
Newsgroups: rec.motorcycles.dirt
Subject: Re: Unsprung weight?
Date: 7 Sep 92 04:23:22 GMT
Organization: CSIRO

> 
>         I fool so feelish for asking but I suppose if I don't know
> 	then I deserve the ridicule.
 
	Mark, Mark, Mark,...you are a mixed up little boy....Parents never
	really got on well did they?....BUT you've shown us that you have
	courage and that your devious mind is chugging away trying to
	grasp an obscure concept. Your bit of lateral thinking has helped
	you come up with what you believe is a solution to the flywheel
	weight fiasco....Naaaa mate, give it a break...

	Is that enough ridicule? Or shall I continue?  ;-^  ;-^

	hee hee hee hee....I kill me sometimes... :-)  I know my wife
	would often love to kill me...
  
> 	So I've never known....  What the complaint is with unsprung
>         weight.  I was thinking back to the (re:flywheel mod) and
>         thought, "Hey, you can get a bigger flywheel on the rear
>     	sproket, but then there goes the unsprung weight again!"

	Two points here...Firstly, the effect of unsprung weight. No,
	let's go back to number zero..what is unsprung weight? It's simply 
	the mass component of all the components not cushioned by the
	suspension from the ground. So, things like the mass of wheels,
	brakes (except for the rear of an ATK which is not mounted on the
	wheel), rear sprocket, disk guards, swingarm (well, a fraction of
	it), axles, tyres, tubes, fork bottom, etc..etc..etc...Anything
	that goes up and down with the wheels...Notice that I say mass
	rather than weight.

	So what you say? Well try this. Grab a pad of paper with both
	hands in front of you and move it up and down as quickly as you
	can. Now drop the pad and pick up two phone big books (ok, just
	one if you're a weenie..) and holding it the same way, move it up
	and down as quickly as you can. Like, WOW! The phone books are
	real slugs aren't they? That's what your wheels are doing when
	trying to follow the track. Notice too that it takes a lot of
	force to make the phone books change direction.....
	
	It's all momentum based and means that the lighter the unsprung 
	weight, the more responsive the wheel is in tracking the track. 
	Which means the wheels have a better chance of keeping in contact 
	with the track = traction....

	....well that's as elequently as I can put it this morning...it 
	was my wife's birthday yesterday and we were out late...

	But, what's this got to do with fly wheel weight (secondly)? SFA
	really..but, if it weren't for the unsprung weight problem, you
	could have a wheel that weighed a couple of tons and it would
	certainly keep the rolling inertia right up there. Nothing would
	stop that wheel from climbing monster hills (except for gravity
	maybe..). You would never get it spinning wildly in the loose stuff...
	much like a weighted fly wheel...Problem is though, that you 
	wouldn't be able to brake with it either, let alone pick it up 
	after dropping it...Actually, you wouldn't be able to corner
	because the wheel's large inertia will fight any turning (much
	like a gyroscope).

	A heavy fly wheel on the other hand has high revolving inertia and
	it too is harder to accelerate or decelerate, but because it spins
	much faster than a bike's wheels, doesn't need to be as heavy
	(it's still momentum based). And, you've got a clutch between it
	and the rear wheel so that you can lock the rear easily for brake
	sliding.....AND you've got low gearing so that the motor can spin
	quickly whilst the wheels don't.

	The physics behind all this is much deeper, but as I said, it was
	a late night.....and this is r.m.dirt after all...

	Got all that?  Good, now go to the top of the class.  ;-)  ;-)
	George C.
Newsgroups: rec.motorcycles.dirt