Why have a lighter flywheel?

[fausTVR]

I know there are some great pulsing brains here in TVR land, so as the above question, what advantage does a lighter flywheel confer?

I understand it will lower the overall weight of the car by a tad and more importantly have less rotational inertia so will spin up more willingly when free revving, but to me it matters more when under load, when the car is in gear and accelerating. In that condition, the flywheel cannot spin up quickly in any case as it has such a great load on it. Is it to do with the engine slowing faster during gear changing perhaps?

[Dominic TVRetto]

This is a complex subject with a number of variables involved including gearing, and has a much greater effect in lower gears.

A very good explanation can be found here:

http://www.pugheaven.co.uk/LIGHTENING%20FLYWHEELS....

...suffice to say that in his theoretical example (not our cars), removing 1kg of weight from the flywheel (5 inches out) has the same effect as removing 39kg from the chassis in first gear...!

By second gear this has dropped to 12kg from the chassis, and in 5th it's down to 3kg - but it gives you some idea of the effect in low gears that removing 7-9kg could have on our overweight flywheels...

HTH,

Dom

Edited by Dominic TVRetto on Wednesday 27th February 01:44

[spitfire4v8]

The guy who wrote that article is mignon on here, well worth reading his posts, always informative. Mostly found (not surprisingly) in the engines and drivetrains section.

[PGNSagaris]

Simply, makes it feel more race car

[sonnylad]

Stops you being lazy when in trafic

[Classic Chim]

Rather than ask why a lighter flywheel if you ask yourself why a heavier one in a production vehicle
The answer to some extent is a heavy flywheel adds inertia to help engine over compression stroke especially at lower revs when engine power is low and engine resistance is high.

So a heavier one at higher revs is then effectively working in reverse and dragging power away.
So light flywheel for a high rev engine
Heavier flywheel for slow speed manners or a low revvin engine is how I see it.
Clearly the lighter it is the less weight applied on engine so it should spin up faster or accelerate more

[Zeb74]

Idiot question, nobody tried to put a kind a clutch on a flying wheel? So you have an heavy one at low revs and a light one for high revs.

[TwinKam]

Interesting question! It's possible, as it's not the total mass that matters, but how far that mass is from the centre. Weights near the circumference would need to move inwards towards the centre as revs rose, it would need some kind of servo because it would be fighting against the laws of physics. Probably the complication it would add would outweigh any advantage.

[ianwayne]

Aren't you really explaining what a dual mass flywheel does?

They are the spawn of the devil on old cars (DMFs that is) making a clutch change potentially VERY expensive.

[TwinKam]

ianwayne said:

Aren't you really explaining what a dual mass flywheel does?

They are the spawn of the devil on old cars (DMFs that is) making a clutch change potentially VERY expensive.

No. That's not what a DMF is about at all. I don't disagree that they are the devil's own work, but neither of their two 'masses' move in or out relative to the centre of rotation.

[ianwayne]

I hadn't realised that. I've avoided cars with them successfully so far, but I though the springs moved the mass away from the centre of rotation. I stand corrected!

[TwinKam]

ianwayne said:

I hadn't realised that. I've avoided cars with them successfully so far, but I though the springs moved the mass away from the centre of rotation. I stand corrected!

Put simply, the 'cush' is in the flywheel rather than the driven plate.