any advice? about to swap my flywheel

[Jscobey]

Maybe you're not closing the throttle as far as you used to but it is physics.

The lighter mass will both accelerate and decelerate quicker. So when you get quicker rev'ing you automatically get increased engine braking (or quicker deceleration) to go with it.

Yea that's what I'm thinking. I just rode it to go to dinner and did notice the engine braking. I think I'm so taken by the acceleration than I don't notice the decel

[Tweety]

Maybe you're not closing the throttle as far as you used to but it is physics.

The lighter mass will both accelerate and decelerate quicker. So when you get quicker rev'ing you automatically get increased engine braking (or quicker deceleration) to go with it.

Actually, physics say that you get both MORE engine braking, and LESS engine braking... In a way...

Less mass means it will resist change less, ie spin up or spin down faster... That means that while your engine does more of the braking, since the flywheel isn't resisting the change, it also happens faster... Same as the acceleration, you gain quickness in the system, but loose momentum... Shorter and sharper peaks either way...

Which is why it's entirely possible to break the rear loose on engine braking alone with this mod if you are too ham fisted...

[VTRDark]

Inertia and rotating mass!

Markus what's you view on the less mass making the bike harder to start and easier to stall at idle. Everything has it's pro's and cons so it would be good to know what are the cons specifically with the big twins. These are big pistons to move around which requires energy and the rotating mass helps with that.

(:-})

[lloydie]

No cons "I've" found and I've been running one for a while now .

[Tweety]

Inertia and rotating mass!

Markus what's you view on the less mass making the bike harder to start and easier to stall at idle. Everything has it's pro's and cons so it would be good to know what are the cons specifically with the big twins. These are big pistons to move around which requires energy and the rotating mass helps with that.

(:-})

Well... That depends entirely on the engine... On my "street" engine it makes no noticeable difference to starting, it tends to start on the second turn over, or third every time... I'm using a LiFePO4 battery, so first rotation is weak, second is good, and it starts easy... No problems with stalling either... But that engine has a comparatively mild tune... (135-140 Rwhp depending on the weather)

On the race engine, which has an entire different tune, it makes a difference... But that's more a result of the fact that that engine has quite a bit more aggressive cams, and different compression... It's not very easy to start, period... Doesn't much matter what flywheel you use really, it has a nasty morning temper regardless (or well, plain and simple a nasty temper really, come to think of it...) And it's very prone to stalling on idle, or having odd hiccups or carbfarts at just off idle... But that's a compromise I'm willing to live with... 150+ Rwhp has it's drawbacks...

Generally, yes, if your bike is a bit cranky (pun intended) it makes matters worse... But then I'd start finding the reason for that instead of compromising on the lightened flywheel... On a bone stock, or just carbtuned engine, it makes no difference what-so-ever unless the bike has other issues...

[VTRDark]

Cool that makes a lot of sense with the higher comps obviously requiring a bit more and the tighter tolerances of everything on a race bike. It was just something I read on another forum.
http://cbr250.com/forums/general-techni ... -cons.html

I think I recognise the OP's user name there too.

(:-})

[Jscobey]

I think I recognise the OP's user name there too.

(:-})

my username? unless its someone else that has the same username. deffinatley not on any cbr250 forums.

[VTRDark]

Not unless you go under the name of CodeBlue. Isn't there a Hawk member over the pond under the name of CodeBlue.

Found another interesting read. Adding weight to flywheels to control horsepower.

Not surprisingly, many factory riders run flywheel weights on their race bikes. Why? Because they pump out as many as ten more horsepower. The flywheel weight helps tame those ponies.

http://www.thumperfaq.com/mxa_flywheel.htm

Bare in mind they are talking about race bikes though. But interesting!

(:-})

[Delano.l]

I have got to get one of these bad boys

[Jamoi]

Found another interesting read. Adding weight to flywheels to control horsepower.

Not surprisingly, many factory riders run flywheel weights on their race bikes. Why? Because they pump out as many as ten more horsepower. The flywheel weight helps tame those ponies.

http://www.thumperfaq.com/mxa_flywheel.htm

Bare in mind they are talking about race bikes though. But interesting!

(:-})

I used to run a flywheel weight on my 2-stroke YZ250, otherwise the powerband was like a switch!! Fun, until it rips your arms off just before a jump

[fabiostar]

i need to get myself one of these bad boys on the storm.

[VTRDark]

FYI Here is a drawing with Rogers specs for anyone that has a spare flywheel and has the means to get it cut.



(:-})

[Jscobey]

Inertia and rotating mass!

Markus what's you view on the less mass making the bike harder to start and easier to stall at idle. Everything has it's pro's and cons so it would be good to know what are the cons specifically with the big twins. These are big pistons to move around which requires energy and the rotating mass helps with that.

(:-})

Well... That depends entirely on the engine... On my "street" engine it makes no noticeable difference to starting, it tends to start on the second turn over, or third every time... I'm using a LiFePO4 battery, so first rotation is weak, second is good, and it starts easy... No problems with stalling either... But that engine has a comparatively mild tune... (135-140 Rwhp depending on the weather)

On the race engine, which has an entire different tune, it makes a difference... But that's more a result of the fact that that engine has quite a bit more aggressive cams, and different compression... It's not very easy to start, period... Doesn't much matter what flywheel you use really, it has a nasty morning temper regardless (or well, plain and simple a nasty temper really, come to think of it...) And it's very prone to stalling on idle, or having odd hiccups or carbfarts at just off idle... But that's a compromise I'm willing to live with... 150+ Rwhp has it's drawbacks...

Generally, yes, if your bike is a bit cranky (pun intended) it makes matters worse... But then I'd start finding the reason for that instead of compromising on the lightened flywheel... On a bone stock, or just carbtuned engine, it makes no difference what-so-ever unless the bike has other issues...

woah woah woah... hold it! youve got VTR engines pumpin 135-140hp and another pumping out 150ho??

are these two engines that you swap out on one bike? or is it two different bikes?

ive only heard of 150 hp when talking about moriwaki race bikes! i havnt heard of anyone whos got those kinda ponnies. maybe im just misinformed and its more common than i think.

im sure it takes a LOT of time and even more money to get there. really cool though. whats torque numbers and top speeds for those engines?

[Bleh]

This is almost my cup of tea... at least, it's the type of stuff I'm studying!

Lightening the flywheel (or not) comes in to the category of inertia or, moments of inertia to be more precise.
Simply put, MoI (or just I) is a direct relation to the torque required to produce an amount of angular acceleration and is defined by I=mr^2 (or even I=(md^2)/4) and is measured in SI units of kg/m^2 (which, in american terms is something like lb/ft^2 I beleieve. Look at a spec sheet and you'll see it's related to torque)!

So, if I still have your attention, we'll do a little example. Converting the measurements already put up here into stuff I can use, 7lb 5oz = 3.4kg and 6lb 4oz = 2.95kg (mass) and the diameter is 146mm = 0.146m so r = 0.073m.

Heavier one first;
I = mr^2 = 3.4*(0.073^2) = 0.0181 kg/m^2

Lighter one next;
I = mr^2 = 2.95*(0.073^2) = 0.0157 kg/m^2

Now you can see the numbers it's easier to see how you appear to get better acceleration - less effort is needed to rotate the lightened fly wheel which results in the engine being able to get through the rev range quicker.

Basic physics, i.e. newtons law of F=ma, would usually suggest that greater acceleration would equal greater deceleration but things change on a motorcycle and a bit like voodoo, all is not as it seems.There is something which comes into play with motorcycles which is described by an italian professor, Vittore, as reduced mass. This doesn't actually mean it gets any lighter, what it does mean though is that combined properties (of relevant masses, i.e. Crank, Wheels, Cams, etc etc) are taking into consideration when calculating all sorts of aspects of a motorcycles performance and would actually result in a higher reading taken for mass... anyway, back to the point.

As the lighter flywheel has a lesser 'I', due to the lower mass, it's contribution to engine breaking would also be less as it is easier to rotate <--- Am I making sense here?

Putting a lightened flywheel on will have minimal 'cons' if lightened correctly especially for general road use. The immediate 'con' that springs to mind (excluding the loss in engine breaking) would be the potential life of the flywheel. Lesser material would suggest that the ability to dissipate heat would be less effective which can eventually result in fatigue of the component. However, a decent flywheel, lightened or not, without being put through continuous heavy use (i.e. regular racing and very high temperatures) will last as long as the bike.

I wouldn't be to concerned that you're not getting 'as good' engine breaking but instead enjoy the fact that your beast feels like a new bike and if you haven't already, start looking at reputable 'artist' to flow the head and polish the ports. Done well, you'll get magnificent gains even without changing the cams or looking to potentially install larger valves (if they can be done in the VTR head that is - not had one off to inspect yet!).

[gl_s_r]

So as a question is there a limit to how much weight I can remove or will it all be a advantage?