Does reducing ground clearance REALLY reduce drag?

[Otto]

Seems to me, you want to keep air from becoming trapped under the nose, which then lifts and/or jams under the draggy underbody of the car. Hence No. 6 above has lowest drag, lift, and power consumed.

It also seems to me that although the Miata nose planform (as seen from above) could be improved somewhat with a more elliptical shape to make for a smaller stagnation point which sheds the air more efficiently. In other words, droop the nose a bit more, make it more pointy/elliptical, then add the dam/splitter with no concavity.

Start with this and then make those mods:https://encrypted-tbn1.gstatic.com/i...bVOwUHZqImq5wm

The Miata numbers posted above do not include an undertray, but I'd wager that an undertray extending aft from the plane of the splitter of No. 6 would be even better, as would extension of the air dam further laterally to completely shield and fair airflow around the front tires. Finally, using ram air from the stagnation point intake, duct it to the front wheel wells as a BMW-like air curtain.

[radioranger]

So basicly you want to avoid funneling air under the car , direct it outboard as smoothly as possible and vent any excess radiator feed air out the wheel wells, It's all coming together, so it seems those ricer front air dams are good if they do that and avoid the outboard edge brake ducts, This is great stuff and seems intuitive like all good ideas once you see it . my escort nose is rounded under like the Miata so very applicable, now how to do it all on the cheap.Thanks to everyone, this explains my cars poor wind handling and buffeting,

[Otto]

Originally Posted by radioranger

So basicly you want to avoid funneling air under the car , direct it outboard as smoothly as possible and vent any excess radiator feed air out the wheel wells, It's all coming together, so it seems those ricer front air dams are good if they do that and avoid the outboard edge brake ducts, This is great stuff and seems intuitive like all good ideas once you see it . my escort nose is rounded under like the Miata so very applicable, now how to do it all on the cheap.Thanks to everyone, this explains my cars poor wind handling and buffeting,

Using Miata No. 6 as a guide, make air dam out of Home Depot garden edging, around $7 for a 20' roll, if I recall correctly. Make it vertically flush with the leading edge of the front bumper, if possible. Extend laterally to fair and shield the outer leading edges of the front tires.

Add Coroplast undertray, extended ~4" forward of the bottom edge of the garden edging, for a combined undertray/splitter. Extend undertray at least as far aft as the axis of the axles.

You should have~12-13' of garden edging left over. Side skirts?

Next priority is undertray at rear of the car, to smooth any parachutes commonly made by manufacturors under the rear bumper and aft of the gas tank. Wedges of Coro could be used for diffuser, mindful of the Lotus details noted previously on this blog, by me.

Now, you'll have less pesky air jamming under the car and creating unwanted lift and drag, and that air which does go under is smoothed and its exit properly channeled into the wake, which should be much smaller and less draggy.

A discarded 4X8 Coro political sign or two, plus a few bucks on Home Depot or similar garden edging, should very significantly lower your drag, increase your mileage, and make your car quieter and less vulnerable to salty road spray.

[aerohead]

Originally Posted by radioranger

So basicly you want to avoid funneling air under the car , direct it outboard as smoothly as possible and vent any excess radiator feed air out the wheel wells, It's all coming together, so it seems those ricer front air dams are good if they do that and avoid the outboard edge brake ducts, This is great stuff and seems intuitive like all good ideas once you see it . my escort nose is rounded under like the Miata so very applicable, now how to do it all on the cheap.Thanks to everyone, this explains my cars poor wind handling and buffeting,

In 1970,Chrysler engineers responsible for the Daytona Charger development remarked on the following,in their SAE paper:
*The 18-inch,low profile drag nose section allowed a 45-degree angled front spoiler of maximum chord,which would also maintain the NASCAR minimum 6.5-inch ground clearance, while also positioning the spoiler as far forward as possible to minimize the high pressure area in front of the spoiler,which otherwise would create lift if moved aft.
The spoiler also increased the pressure differential across the radiator,which already had adequate cooling flow for the big Hemi,and allowed them to 'grille-block' the Daytona to minimize even more airflow under the car.
*The combination nose/airdam reduced front lift 66% compared to the 1969 'RACE' charger and lowered the Cd from 0.35,to 0.27 (without the rear wing/stabilizer setup).
--------------------------------------------------------------------------
You can look at contemporary NASCAR racers and see how nearly the whole nose is an airdam.

[bondvagabond]

Originally Posted by diesel_john

I got this brillant idea a couple years back that my windshield was too steep and needed to be tilted back, so, I cut a couple inches of an old set of rear springs and put them in. (under body stock)

Well it just killed my top end and mileage, so I put the stock springs back in.
Mileage and top end back to normal.

So I wonder if I raise the rear an inch what will it do?

My shade tree engineer guess as to why this happened was that you created a wedge under your car, where the air was compressed going from the front to the back creating a bunch of drag.

[bondvagabond]

I think part of what is going on when lowering a car helps cd is that the super dirty suspension members are being retracted up into the less dirty underside of the vehicle, the most common method of lowering being 1.shorten springs 2. Correct front alignment 3. Reduce tire size as needed to fit hole.

Less obvious on cars but look up the bloomers of a truck and you can see big giant suspension members that get smaller as they compress.

[aerohead]

Originally Posted by bondvagabond

My shade tree engineer guess as to why this happened was that you created a wedge under your car, where the air was compressed going from the front to the back creating a bunch of drag.

Not to be nit-picking,but technically,air does not compress below 250 mph.
The 'wedge' would as you mentioned,expose otherwise shielded components,increasing interference drag,and there would be an acceleration of the air,increasing the boundary layer under there.
Since the air was acting against the underbody,it would create lift.
The angle would also change the angle of attack of all the upperbody surfaces,creating a more hostile pressure environment,which could lead to premature separation.
ALL bad!