AviationBanter - View Single Post

**Charles Vincent**

wrote:
In rec.aviation.piloting Charles Vincent wrote:
wrote:

The biggest source of drag on a car is air followed by tires.

Of course the makers are going to put hard tires on as well as
streamline the vehicle to get mileage up.

The less drag, the less gas the vehicle uses.

What's your point?

That is only true in cruise on the highway. In stop and go city driving
driveline friction is the majority, followed by inertia. Air and tire
is a small percentage combined.

Inertia is not drag.

Inertia is F=ma.

In stop and go driving, F=ma dominates.

If it didn't, hybrids converting the F in deceleration into energy in
the batteries instead of heat in the brakes wouldn't get their high
mileage numbers.

Yes Jim, I knew the difference, and I see you know too. I had assumed
you also knew the difference between aerodynamic drag and rolling
friction when you lumped then together in your statement "The biggest
source of drag on a car is air followed by tires." I figured you were
using drag in a more generalized way rather than jumping to the
conclusion you just didn't know the difference. Since you are insisting
on being pedantic, then I will have to point out that inertia is really
just the m in F=ma, the formula just establishes a relationship between
the property of mass called inertia and force and acceleration. I
expect that the manufacturers are working to reduce all of the
"retarding" forces on their vehicles, which benefit them without regard
to the motive source. Electric vehicles can have an advantage in the
regime where inertia is the dominate "retarding" force and a
disadvantage where it is not.

Charles