Spec_Ops2087

You want less "lift"

You can't want less aerodynamics, that doesn't make sense.

Incubus

I've got three words: Emergency Lane Change.

A Hummer at 70 mph w/ half of its traction is going to be nothing but a projectile.

...but seriously, it takes away from the energy you use to go forward to get that lift. That, in and of itself, will reduce your mpg.

ace123

the problem is the lift reduces the normal force on your tires, thereby reducing your traction available to corner, brake, or accelerate. lift doesn't make the car lose any mass, and momentum is directly proportionate to vehicle mass.

so basically, adding lift will hurt braking, cornering, and acceleration because the mass is the same and the tires can't get as much grip.

txjeepn

Yes, it was a comical reply to a question, which has been answered over and over. I

PanteraKitty

I find it hilarious to use aerodynamics and Hummer in the same sentence. A Hummer has the aerodynamics of a 6,000 lb. house brick.

mxt_77

This is the closest thing to the "correct" answer, as far as I'm concerned. The truck's behavior will be affected by a summation of forces. So, if you have this wing on your Hummer, you not only have to generate enough force to move the truck forward, but you also have to generate enough force to create this "lift" which is acting on the truck to counteract the amount of force that it puts on the road (i.e., it's "weight"). This lift is generated by aerodynamics, which adds a "drag" component. This drag component effectively pulls the truck backwards, which means that the engine has to work that much harder to keep the truck moving at a constant speed.

So, in the end, you are requiring more force to move the truck down the road at the same speed. More force requires more power which requires more fuel.

And, yeah... there's also that nasty side-effect of decreasing the force which provides traction, thereby making it that much more difficult to stop the 8000lb truck that's barrelling down the road at 70mph.

Kremlin

Even if you could generate lift without creating any drag, it would not be beneficial. Mass != Weight. Adding lift to reduce the effective weight does not reduce the vehicle's MASS which is what slows it down. A car with 5000 pounds of weight and 5000 pounds of mass accelerates at the same speed as a car with 10000 pounds of weight and 5000 pounds of mass, assuming other parameters are equal.

mxt_77

What if they're going uphill?

ZDan

Mass isn't what slows the car down. Mass is what makes the vehicle RESIST slowing down. Or speeding up. Or cornering.

The forces acting to slow the car down are rolling resistance and aerodynamic drag. If you were able to get LIFT without inducing drag, you WOULD see an improvement in mpg since rolling resistance would be reduced.

In the real world, lift will create more aero drag than would be compensated for by decreased rolling resistance.

If you have a car that develops lift naturally (like my 240Z), reductions in lift via aero aids can both reduce drag AND increase traction at speed on the track.

Kremlin

I was attempting to simplify my explanation to someone who is under the impression that creating lift on a Hummer can make a 6000 pound Hummer drive like a 3000 pound car.