Lightweight FlyWheel - myth?

[EZcheese15]

The only "torque" you loose is launch torque. That's something you don't need on a roadcourse. Ever see a pit crew pushing a car out of the pits to get it started? That's because the flywheel is so light they can't even get the car to start moving.

I honestly can't think of a reason that a heavier flywheel would *not* benefit your 1/4 mile time.

The only thing is this:A lightweight flywheel *will* show a small gain of HP on a chassis dyno because it is less rotating mass. However, the question is this, which is better? Less Rotating Mass or a Higher Moment of Inertia? I suppose this is why some people see 1/4 mile benefits and some people don't. I would imagine the less powerful the car is, the more the rotating mass makes a difference. On a higher power car, the benefit of that extra 2 HP is overcome by a large moment of inertia of the flywheel which can greatly increase launch time.

[cdlong]

you guys need to study physics a little more.

The reason you lost time on a 1/4 mile is because the lighter flywheel has a lower moment of inertia. When the car is revved at the start, you increase the inertia. A lighter flywheel has less of an increase, while a heavier one would have more of an increase.

When the car is launched, with a HIGH moment of inertia, the inertia of the flywheel actually helps to accelerate the vehicle faster because the engine has to do less work to get the car moving. With a lighter flywheel, and LOWER moment of inertia, the engine has to work harder to accelerate the car. For this reason, a Pro Drag racer will opt for a HEAVIER than stock flywheel.

the additional inertia you can store up in a flywheel isn't enough to really move the car. and any power you put out after the launch goes into accelerating the car and the flywheel. heavier flywheels are better for drag racing (to an extent) because it makes launching easier. it smooths things out, helping you maintain traction.

ive always figured that a lightened driveshaft would be just as beneficial but less detrimental

the benefit of a lightweight flywheel is also it's disadvantage. if it accelerates (spins up) faster, it will also decelerate faster. the same holds true for everything, driveshafts, brake rotors, anything with mass (though this discussion is about rotational inertia).

[EZcheese15]

you guys need to study physics a little more.

the additional inertia you can store up in a flywheel isn't enough to really move the car. and any power you put out after the launch goes into accelerating the car and the flywheel. heavier flywheels are better for drag racing (to an extent) because it makes launching easier. it smooths things out, helping you maintain traction.

No, it's not enough inertia to *move* the car. However, the inertia that is stored when the flywheel is spinning in neutral transfers throughout the drivetrain when the clutch is engaged. The inertia from the flywheel does *aid* in transfering the inertia to the wheels. Because of this, the engine is required to do LESS work to get the car moving. I never said the inertia in the flywheel would *launch* the car, I said it would reduce the work load on the engine during launch, which in turn allows the engine to utilize it's power to increase the inertia of the vehicle even more.

[D-UNIT]

The only "torque" you loose is launch torque. That's something you don't need on a roadcourse. Ever see a pit crew pushing a car out of the pits to get it started? That's because the flywheel is so light they can't even get the car to start moving.

I honestly can't think of a reason that a heavier flywheel would *not* benefit your 1/4 mile time.

What about when going up hill?

Full race cars don't have a lot of torque yes , but at the start of every race they actually do a standing start. I've even seen them do burnouts and doughnuts. But your right about drag though. I was watching HP TV and they were selling "race " flywheels starting at 25lbs all the way to 50lbs!! V8 of course.

I'm guessing here , but I think lightweight flywheels are more crucial to perfomance in NA cars than turbo cars ( note my friends times in the first post).

[C-Kwik]

Actually, it's momentum, not inertia, that is crucial. Semantics. But yes, a heavier flywheel naturally has more mass which allows you to store more potential energy. When you release the clutch you use some of this energy combined also with some output from the motor to get the car moving. A lightweight flywheel will have less stored energy to begin with so you end up needing more output from the motor to get it started in the same manner. This will actually require more throttle modulation. In drag racing, if you have the right set-up, a light weight flywheel can get you down the strip faster. Since a function of the momentum you need to get the car is also the speed of the flywheel, you can simply rev higher. If you're tires are sticky enough to hold the road, a simple drop-clutch start will get you out of the hole quite quickly. Coupled with the lower rotational mass, and in the case of a turbo car, slightly better turbo spool, you might shave a few tenths off. But it wil not be comfortable trying to drive your car like this in traffic or from light to light.

[Dattebayo]

Couldnt you fein rotational mass by simply using a dense material as a ring with spokes design flywheel instead of just a solid design?

[Nismo_Freak]

Couldnt you fein rotational mass by simply using a dense material as a ring with spokes design flywheel instead of just a solid design?

You would negate the benefit of the lighter wheel by doing that.

[skydragoness]

Whoa.This is interesting to me, I bought a Fidanza a year and a half ago. I do some autoxing, but the car is also a daily-driver. Should i sell my Fidanza then? I don't want my car to suck more than it already does, and i was thinking of going with a RPS or ACT clutch to go with the Fidanza. Argh.

[colies97~240sx]

sky, i wouldnt go selling it, unless you are wanting to make it a drag car... of if you race people off the line at stop lights all the time i am completely happy with mine as a daily and have no regrets about getting the fidenza. and as i understand a lightend flywheel is good in track events like autox ect.

[nab911]

The only reason why a lightwheel fw wouldnt be good is when you are shifting. If you get up to 6500 in one gear and you dont shift fast enough the revs could drop below what they should be matched to in the next gear, thus the car would slight slow down to match the motor. If you shift fast enough, you can let it out with the revs higher than the transmission speed, thus giving the car a quick boost while it tries to catch the motors revs. Its all in the wrist... and the hips