[Shazaam!]

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.