Well I went with the garden stuff and wrapped it around from the front of the wheel well (to cover the wheels) on each side and had it stop 4" from the ground. Went out and did a quick test on a 8 mile north south run with cruise control set at 60. Wind was out of the south at 12 MPH and the temp was 90 degrees.

Water coolant temp was 10 cooler(184 instead of 195). It actually decrease my FE I think that the excess drag does not make up for the reduced airflow under the car.

Air Dam 42.6 37.9 AVG 40.25

Without 42.7 38.8 AVG 40.75

Although this was just two run the runs into the wind showed a big decrease. The runs with the wind about the same but the equivalent speed would of been 48 and 72 respectively.

So no air dam for me.

air dam
 

They do add a bunch of frontal area. I would say they are more for looks on cars. I dont know if one test is worth trashing the idea though.

a poorly designed lip or air damn will increase the frontal area.

the well designed lips stop air from getting under then car but only to a small extent(the lowest point of the underbody). all of the honda oem lips do this and then go down further in front of the tires to smoothly direct air away from them.

Is the air-dam straight across? If so maybe bring the center out towards the front of the car so it's more of a V, might cut some of the drag.

Ben,

What stores have you seen the " carpet molding/lining stuff." I think I know what you are talking about but where to purchase it?

Yeah! I'm actually going to try to put on an air dam tommorow with sheet metal, and I think that "v" idea would/could also give it strength. Still trying to figure something out tho: Since my car is 7 inches off the ground, how low and how wide would the dam need to be to be most affective!?

I remember Phil Knox saying a 3" ground clearance is ideal for a road car.

not in america

True. Most roads in the US aren't suitable for that ground clearance. But if you want optimized aerodynamics, above all else...

I am planning on lowering my Triumph to a 3" ride height. Just have to be diligent to avoid any curbs, potholes, or road debris, and be very careful around speed bumps. I recall that stock, he Mk I and II have a 4" ground clearance, the III a 5" clearance.

3" to the bottom of the frame??? That will be quite an adventure - you'd get high-centered driving around here. The short wheelbase of a Triumph will help, but I have a '77 Camaro and I'll scrape my exhaust going in/out of some parking lots. The exhaust has about 4-4.5" clearance.

Regarding side-skirt placement, would it be better to push the skirts out to where the outer edge of the wheel is, or just wherever is convenient?