Lightweight Flywheels

Comments by Jack Money

The real downside, if you are concerned about it, is that a LTW flywheel will typically allow gear rattle inside the trans. One of the purposes of the heavier, or twin mass, flywheel is that its rotating inertia "absorbs" small changes in engine RPM. This works in part to effect a change in natural frequencies which exist in the system. It's sort of a mass damper if you will. The other part of that is simply the mass.

Another reason is that it allows the vehicle to decelerate at a slower rate when in a state of engine braking. The intertia of heavier flywheel works against combustion pressure, less mass equals more uncountered combustion pressure to slow the engine and thus the car. A LTW flywheel, especially one with significantly less mass, will allow the engine to slow quicker, it has less mass momentum to work with.

For track applications especially, these are of no concern. And the gear rattle thing will not necessarily occur in all vehicles. In my first M3 I had the GrpN flywheel and never experienced any gear rattle. Certainly wear in the transmission will be part of this equation as well as tolerances of internal parts and such.

Bottom line is that it is unlikely that you will experience any real negative effects, even an idle issue. What you may notice initially at idle is more of a lumpiness, the ability of the rotating inertia to absorb small RPM variations has decreased.

Do it....and if you're going to do it, buy the aluminum 8lb version. You're in there, you might as well get the bigger change!

Jack Money

Bay Area ///Motorsport

Last updated on 29 January, 2003 12:32 PST