balancing.

[treed2 at wsu.edu (T. Reed)]

> * No, or not exactly...  I am saying that you will not have to change the
> throttle position as frequently, with road changes, wind, etc...  As in, say
> you are at 70...  A strong wind comes up, and you have to make a speed
> correction to maintain the same speed...  You have more inertia with the
> stock flywheel, therefore you will have to depress the throttle less to
> maintain the same speed...  Not only wind of course, but also with slight
> hills, overcoming semis, whathaveyou...

Okay, now I'm regretting what I just did. I just deleted about 3 long
paragraphs of explanation that pertains to this very thing because I
decided it wasn't relevant and I didn't want to waste everyone's time
with it. That was stupid, now I have to explain myself again. I think I'm
going to approach this from a different angle, though..


Tell me what's wrong with this argument:

When you climb a hill in a car, you're not going any faster, the road is
just more vertical. So, the acceleration at the flywheel is zero; it is
still moving at a constant speed. The engine is just working harder than
it was before you started climbing the hill, it's not spinning any faster
or slower.

Therefore I conclude that the flywheel weight has no effect when
climbing hills. This is based on our previous agreement that the flywheel
weight doesn't matter when you're moving at a constant speed.


Now take wind gusts.. it is true that the flywheel weight contributes
ever so slightly to the overall momentum of the car when the car is in
gear. So yes, a sudden wind gust will slow a car that is in gear and has
a lightened flywheel more than a car that is in gear and has a regular
flywheel. But not by much, because the engine is mechanically connected to
the wheels and you're maintaining a constant throttle position. The speed
will dip slightly then return to where it was. The dip might be a little
bit less pronounced with a heavier flywheel, but won't go away completely.


As far as driving up one side of a hill and then back down again, this is
similar to the braking energy explanation. You're storing potential energy
in the mass of the car as you drive up the hill. A car with a heavier
flywheel is just storing more energy on top of that. As you drive down the
hill you will have to use the brakes to dump the energy from the extra
flywheel mass as well as from climbing the hill.


So the only thing that could possibly affect mpg would be wind gusts (and
only gusts because constant winds fall under the category of friction) and
the effect it will have (if any) is absolutely miniscule compared to the
effect of spinning the extra mass of a heavier flywheel up and down
through every single gear change and at every stop light.

Which brings up one more thing-- the fuel dumped in to the engine is
determined by the air flow plate position, not the throttle position. If
your foot is off the gas and your engine is winding down it's still
getting fuel (albeit less than usual, at least with cis-e, because of
deceleration en-lean-ment) because the air flow plate is still lifted
even if the throttle body is closed. The engine spins down faster with a
light flywheel, thus more fuel savings.

-Toby