Anyone made/fitted a lightweight flywheel?

[slowpoke]

It's quite a common and effective mod to fit a lightweight flywheel to a Ducati yet it seems unheard of to do it to anything else. I fitted one of these luvverly superlightweight Nichols units (http://www.nicholsmfg.com/flywheel.html) to my old 916SP and it made a noticeable difference to throttle response without any apparent negative effects. FYI, the 916 flywheel was very similar to the R1 flywheel shown below.

So, why doesn't anybody manufacture something similar for other bikes?

Checking out my R1 in particular (and lots of others generally) all the serious race bikes dump the flywheel, stator and starter gears for reduced rotating mass. This gives sharper throttle response, less engine braking (less need for expensive slipper clutch) and better handling. When I first acquired my bike that's exactly how it came, straight off the track, with a fabricated plate covering the bare end of the crank.

So my question is: can anyone see a problem with turning down a stock OEM flywheel (the cheap option on Ducati's) to drop some rotating mass?

Has anybody done this? If not, why not?

[johan]

Here's a good write up on the pros/cons of the lighter flywheel.

http://www.ducati.ms/forums/showthread.php?t=29734

[Paul in NZ]

Depends...

The likes of Triumph experimented with different flywheel weights and heaps of people used to lighten them. Moto Guzzi LeMans's (proper ones) have a lighter flywheel than an SP or T3 etc and aftermarket light ones are common.

A single cylinder bike or a V Twin needs a flywheel to smooth out the power pulses due to limited power pulses per degree of crank rotation.

Sporting line 4's usually run a pretty minimal flywheel as it is and I doubt the would be much gain over what the factory already sets.

[Motu]

The flywheel is one of the most important parts of an engine,and yet doesn't effect power at all.You can take the most radical lumpy,cammy engine,one that is hard to start,won't idle with a massive power surge when the cams kick in - fit a 3 foot cast iron flywheel and it will start by hand,idle smooth and quietly,and produce smooth power.Take the flywheel off a plonking tractor motor and it will be very difficult to start and won't idle.

As Paul says,Triumph used several flywheel weights in the twins,and I used to search for the light flywheels (1962 was lightest I think).With a bit more experience,I started to look for the heaviest flywheels.

[xwhatsit]

I want a heavier flywheel!

Wonder if an XL500 flywheel would fit?

[slowpoke]

Depends...

Sporting line 4's usually run a pretty minimal flywheel as it is and I doubt the would be much gain over what the factory already sets.

I'm not at home for a few weeks yet but from memory holding the flywheel in my hand (see photo above) it wasn't any lightweight. As you can see most of the weight is in the outer ring, which rotates outside the stator unlike a lot of other bikes which have the rotor (and hence most of the weight) rotating inside a similar sized stator for much less inertia and gyroscopic effect.

The flywheel is one of the most important parts of an engine,and yet doesn't effect power at all.You can take the most radical lumpy,cammy engine,one that is hard to start,won't idle with a massive power surge when the cams kick in - fit a 3 foot cast iron flywheel and it will start by hand,idle smooth and quietly,and produce smooth power.Take the flywheel off a plonking tractor motor and it will be very difficult to start and won't idle. I agree that they won't idle as well but I reckon it would be easier to actually get an engine to fire with less flywheel as it would spin up quicker.
As Paul says,Triumph used several flywheel weights in the twins,and I used to search for the light flywheels (1962 was lightest I think).With a bit more experience,I started to look for the heaviest flywheels.

Yes, power itself is unchanged regardless of how heavy a flywheel is, but the ability of the engine to accelerate/decelerate and the ease with which the bike can change direction is massively affected.

To compare the extremes, a single cylinder Honda CR250 crank, rod and piston are comfortably held in one hand and probably weigh the same as my R1 flywheel alone. Hence it produces instant power which can be a disadvantage in soft going as the tendency is to spin up rather than go forward, even in a straight line in top gear it's easy enough to break traction. As a result extra flywheel weights are a often used to soften the power pulses and gain more traction. Same power just delivered in a slightly different way.

On the other hand a 1000cc, four cylinder, crank rods, pistons etc weigh many times as much as the CR250 (flywheel is smaller percentage of rotating mass) and it is used on a surface which is comparatively extremely grippy. Unlike the CR250, in a straight line it is impossible to break traction using the throttle alone on a dry road. So why not increase the ability of the engine to accelerate and take advantage of that traction?

The four cylinder is inherently smooth compared to a twin or single so vibration shouldn't be a major drama. The other point to note is that my ol' girl has carbs not fuel injection, so there isn't the instant hit that has been the bane of some FI systems.

I dunno, I'm leaning towards the fact that bikes, especially Japanese bikes, are designed to be inoffensive, sanitised and appealing to the broadest possible market whilst meeting strict regulations. They have to be able to potter through rush hour traffic, idle smoothly, have little or no vibration etc. I on the other hand live in the country so don't potter in traffic, enjoy sports/track day riding, don't care about a slightly higher/lumpier idle or non-EuroIII emissions, can't afford/justify lightweight wheels/slipper clutch for similar effect and ultimately need all the help I can get to go faster on the track with an obsolete bike and lack of talent (helluva combination, eh?).....not to mention I'm just plain curious after liking the effect it had on my 916.

Aaaah fuggit, I'll find out when I get home if the flywheel will fit my wee mini-lathe and that, will be the deciding factor.

Pic below is of a lighweight alternator available at www.durbahn.de....rotor is 350grams compared to what is 1.5 -2kg's average flywheel. Very positive recommendations from customers........but not cheap.