Lowering effect on aero...
 

How would lowering effect aerodynamics? I've always heard jacked up vehicles are less aerodynamic and vehicles that are lowered are more, but how does this work exactly? You have air going over and under the vehicle in both scenarios...

I've always thought my Metro to have a high stance, and after removing over 100lbs from the "dry curb weight", it sits even higher. I can double stack my fists between the tire and wheel well.

Have heard from several folks with chrysler minivans (1st and 2nd gen), that installing sport springs on the front (Usually from a dodge daytona) resulting in a drop of about 2 inches just at the front, has improved highway mpg by 5-10% ... lowering the back of these vans isn't very easy, so this gives the van a bit of rake.

Myself I'd like to figure some active suspension mod to bring it down a bit on the highway. I find I need the stock ground clearance on rough tracks, parking lot ramps, speed bumps, and in winter, so would likely have problems with a permanent drop. (And if I could give it 2 inches at low speed as well as lose 2 at high speed I'd be very happy)

I think mine could be dropped 3-4" without any problem, but I'd probably only go like 2"ish.

I was thinking about making some temporary clamps to experiment with. I have coil springs in the rear which should be no problem, but struts up front. Would that still work?

Less air is under the car, which means less air pushes against your car. You need more power to push against more air...

Try driving into a high head wind and you'll notice your mpg drop significantly. Same effect with lowering car. Less wind pushes against your car and you gain mpg.

Basically a lowered car has the tires/wheels tucked behind the body better.

A bumpy underbody produces more drag from 'ground effect' if the car is lowered, but this is a minor effect. Even a smooth underbody has some drag from ground effect.

'struts' is just a term for a coil-over-shock setup. you still have coil springs up front

The most basic answer to the original question is that lowering reduces frontal surface area by the amount of tire surface displaced into the vehicle body.

I don't honestly think you can count on any other significant effect from lowering, though YMMV.

One might note however that NASA in calculating frontal area for truck aerodynamics studies chose to measure height from the ground, not height of body neglecting wheels.

it increases aero. but it throws off alignment and accelerates tire wear.

I lowered my truck 4" in front and 6" in the rear. Sport truck guys call this a "slam." I was able to find a drop I-Beam kit for my 4x2 Ford F-350. It lowered cab height by 4" and resulted in a gain of 1 mpg. My slam kit was 3"/6" but I lowered the front an extra inch with smaller tires going from 235-85x16E to 225-75x16E.

In my case, the truck handles better.