Lightened flywheel - Pros and Cons?
 

How much advantage is there of fitting a lightened flywheel?

I assume that the engine will spin up quicker, but also give less engine braking?

As I'm getting tons of false neutrals, I am hardly getting engine braking anyway;)

So who's fitted one and would you recommend it?

Oh yeh - how much are they?:o

Ta
Tim

I fitted a lightweight flywheel to my 998R.
I also fitted a slipper clutch at the same time.
It has made the engine a bit quicker to rev but the downside is that you have to rev the bike a lot more when pulling away from junctions.
You have to almost ride the bike like a two stroke.
The other point i would like to state is that you will get more engine braking not less.
The standard heavy flywheel wants to keep turning the engine,when you have the lightweight flywheel there is not a lot of weight to keep the motor turning,the engine slows down a lot quicker.
If you are going to fit a lightened flywheel i would suggest fitting a slipper clutch at the same time.
If you don't have one already.:)
I got a Bucci flywheel from John Hackett for £90.

[Edited on 19-5-2003 by sps955]

Thanks for the info, I do have a STM slipper fitted, but strangely, I only really started to get the false neutrals once I'd fitted it.

I assume that the flywheel is easy to swap?

If it feels like a 2-stroke - fantastic, it'll take me back to the old LC days!!!

Tim

Do either of you guys get that initial screech sound from your clutch, when you pull away?

Clutch Screech!
 

Interesting reading the flywheel/clutch comments. My clutch screaches so badly when i try to pull away that fast get aways are impossible. I`m told this is normal on my 998s but i have been blown away by milk floats every time i pull away, very embarassing! Comments!

I fitted a lightened flywheel to replace my already lighted SPS flywheel. It gave me more engine braking and definitely needs a bit more revs when moving off, I also found the engine didn't want to idle until it was fully up to temperature.

As for the screeching clutch, I have the Bicci Slipper that worked great, and then I fitted a set of carbon plates. It now sounds like a slipping fan belt every time I take off. I found I had to learn a new riding technique, let the clutch out fully before gunning it, and don't use the clutch when pulling up the front.:roll:

I\'ve never suffered a screeching clutch...
 

But would rather have that than false neutrals!!!

Tim

Just another thought......
 

I realise that you guys who have lightened flywheels woudl knwo best, and not trying to be too controversial with this one, but if the flywheel is lightened, wouldn't this create less engine resistance when using engine braking?

ie, you would need more engine revs to create the same level of engine resistance, as the engine turns over more easily with a lightnened flywheel?

Therefore engine braking at the same given revs would be less?

Wouldn't it?

I know that Dibble will be along shortly with his flux capacitor theory - so c'mon Dibbs, lets have it!!!

Tim

Basically with a lighter flywheel, then engine spins up quicker, but the revs also fall quicker, which tries to slow the wheel down. Think of gears; you get a lot more engine breaking in first than in third because the engine accelerates and decelerates quicker.

Then again I might be just talking bullsh*t!:D

OK, but.....
 

As you say the engine spins down (slows) quicker as there is less resistance, ie. less engine braking! - which supports my theory!

You have more engine braking in first than in third, because you need more revolutions of the engine for a given revolution of the rear wheel! Hence greater resistance.

I'm happy to be proved wrong on this, so all comments (except Dibble's) welcome!

Tim

Something to do with the stored energy in the flywheel ( inertia )
IE if its heavier (flywheel) then the engine will store more enegry & lose it less quicky
IE if its lighter (flywheel) then the engine will store less engergy & lose it quicker

Can't coment on the Engine baking theory though !
Can't remember that bit !
I went through this before when considering a lighter flywheel for my MK1 Golf GTI , i was directed to a web site in America who went through the pros/cons in Great detail

I have a lightened flywheel and slipper on my 853 and it definately:

1.Revs quicker
2.doesn't like to idle when cold
3.has more engine braking(i don't know why-where's Shazzam!)
4.Only get false neutrals when doddering about and not riding the thing properly.

Engine breaking is caused by the engine slowing down which as a result slows the rear wheel down, so the quicker the engine loses revs the quicker the rear wheel will slow down, lighter flywheel means the engine gains and loses revs quicker due to lower inertia, which is why you'd definitely need a slipper clutch to change down to 2nd or 1st gear in a "spirited" fashion!:cool:

Blimey!
 

maybe i need to start putting an exclamation mark next to my name:lol:

You will get more engine braking with less interia on the crank.

Think of it this way. With the engine at a high RPM, the inertia of the flywheel (or any other inertia in the drive train, such as the clutch) will want to keep the engine spinning as you close the throttle. The engine needs to absorb the energy stored in the flywheel.

So, as you reduce the inertia of the drive train, e.g. lighter flywheel, lighter clutch assembly, the engine will slow down quicker since there is less inertia trying to keep it spinning, hence more engine braking.

The downside of lighter flywheels and clutch, as pointed out already by some people, is the effect on idle. The inertia of the flywheel tends to smooth out the idle. Take away the inertia and your idle becomes lumpy. You may even need to increase the idle speed to keep it from stalling.

I run a very light flywheel and clutch and it makes for a great performing engine, but the idle is very poor. This is amplified by the particular throttle bodies, so mine may not be a good example of what you find with a street bike. I know of quite a few people that run lighter flywheels and they have almost no negative side effects. It will almost definitely make want to install a slipper clutch due to the increase in engine braking.

Pros and Cons
 

Pros and Cons

The weight of the stock flywheel is selected by Ducati test riders to provide a overall balance between performance and smooth drive train behavior. If you remove weight from the flywheel (and to a lesser degree, the clutch) the overall effect is indistinguishable from increasing your engine’s torque output.

With more torque on-hand comes the benefit of faster acceleration if you can modulate the wheel spin driving out of corners. Factory racebikes make so much power, for example, that transmitting the power to the road effectively becomes the limiting factor so heavier flywheels actually become a benefit. Fear the highside.

The ability of an engine with a lightened flywheel to spin-up more quickly is often pointed-to as a benefit when you bang a downshift and wheel chatter is reduced. In this situation, it can be said you have less engine braking. If your riding “style” makes this an issue, a slipper clutch may be a better alternative than a lightened flywheel, at least that’s what the factory racers think. A lightened flywheel is like a poor man’s slipper clutch in this situation.

The ability of an engine with a lightened flywheel to spin-down more quickly is often pointed-to as a benefit if you want the revs to die as fast as possible when you lift the throttle for a corner. In this situation, it can be said you have more engine braking. Under normal riding conditions we tend to prefer less engine braking so we tolerate a less efficient situation where the motor then has to work harder to put more momentum into the flywheel. When racing, you don’t care about storing momentum, you just want to get around the track as fast as possible so a slipper clutch is used to will reduce engine braking.

The purpose of the flywheel is to store momentum, reduce vibration and smooth out the loads transmitted to the drive train. It takes energy to first store this momentum, so if the flywheel is lighter it takes less energy and it accelerates up to speed faster. There is an opposite effect when you lift off the throttle and momentum is given up, so the revs drop slower for a heavier flywheel.

Because the engine will spin up more quickly with a lighter flywheel, you’ll have better throttle response, but modulating the throttle (especially in the rain) will be more difficult if your throttle position sensor, idle and CO are not adjusted properly. A light flywheel seem to exacerbate a poorly set-up fuel injection system. If you make 100 rear wheel horsepower it’s less of a issue. Make 130 hp and it will matter a whole lot more.

The amount of weight removed from the flywheel and inner hub is proportional to this effect, although if you remove most of the weight from the outer rim area, the effect is stronger. Different aftermarket manufacturers of flywheels offer different weights and geometry. If lightweight is good, ultra-lightweight is better doesn’t apply here. Too light a flywheel can make the bike a handfull to ride so a two pound weight reduction for the street may be a good choice.

A cold engine runs rough until there’s enough heat to vaporize the fuel, so until then, a lighter flywheel will be less effective in preventing stalls, especially pulling away from a stop uphill. You’ll need rev the engine a little higher to compensate and you may find it’s a little ornery when running at light load (3,000 to 4,000 RPM) in the lower gears in the city.

I left mine stock.

Shazaam - you da man!!!
 

Does he eat tec books or what?:ninja:

Shaz,you never fail to amaze me!

I've had an ally flywheel on my 748 for about a year now.
no downsides, still ticks over well, doesn't stall, engine braking is stronger and the thing revs up quicker...........
What could happen is that the reduced inertia could exagerate a poor fuelling setup.
Have to agree with Shazaam on all his points ;)
Cost about a £100, fitted in a couple of hours comfortably. I think it's one of the best mods you can do :D

Does a SPS have a lightened flywheel as standard?
Tim

Just a couple of observations while totally agreeing with Shazaam!
A single cylinder engine on compression stroke with a shut throttle is basically trying to stall, this effect is reduced by either adding extra cylinders with different firing orders, hence multi-cylinder bikes having less engine braking for a equal compression ratio, or as already mentioned increasing the inertia, ie a heavier bottom end, hence race bikes using lightened and ballanced crankshafts for better engine response.
On a race bike more engine braking is often a good thing, especially on a twin when combined with a slipper clutch, as it is easier to change the bikes direction when the engine revs are lower due to the gyroscopic effect of all that mass/inertia trying to travel in one direction.
There was something else I was going to add but its slipped my mind at present, poor old brains on over drive preparing two bikes for the TT, 48hrs from now and I will be on the Ferry.

No. The SPS or any other street bike to my knowledge did not come with alloy flywheels. Surely, someone will correct my error, though.

How much engine braking do you get with a slipper clutch or can it be set up to only work on or close to wheel lock-up ?

Would a slipper clutch be able to cope with 6000miles a year or would I be spending a fortune on clutch plates ?

Had a 900ss which made strange noises when setting off (sounded as if chain was jumping the cogs.) and this proved to be problems with the clutch (standard clutch)
and was repaired under warranty because it was only 2 weeks old.

Slipper Clutch...
 

"How much engine braking" is a difficult one to answer - lots!!;)

The slipper clutch is designed not to lock up the back wheel when you've changed down through the gears.

So in theory you'll get maximum engine braking without locking up the wheels. As I've been having false neutral issues anyway, I've found myself going down a lot more than normal without meaning to (in my anxiety to get any gear!) and found that the clutch just releases (slips) as much as it can without locking the wheel up. (am I repeating myself);)?

As for mileage, no reason why it shouldn't last a long time, unless your racing every weekend! - So depends upon use really

Tim