I'm wondering how much I can improve the stock airflow (ie, get rid of floatiness, make the car more stable at high speeds, etc) without turning the car into a nightmare that takes damage any time I go over a speed bump or enter a badly designed parking lot. I tried a few experiments with air dams/splitters in the past but I don't think I knew what I was doing and they really made me appreciate how marginal a lowered miata's ground clearance really is.

The only obvious candidates I can think of for improvement are the parachute-like rear bumper and the area in front of and under the front bumper/front wheel.

Also, does that under-engine plastic cladding help much? I got rid of mine to help with maintenance, wondering if I should put it back.

 

The under tray helps immensely. Bumper cut is easy and obviously streetable as you said.

 

In for some opinions on this. I'm tempted to do a partial flat bottom and small splitter just to help with drag/ lift on faster back roads.

 

Yes the engine undertray is not optional if you want your radiator to work properly (unless you make your own undertray/splitter which many here have done). I wouldn't be surprised if it also improved aerodynamics marginally. And yes, it's a pain in the *** to take off every time you want to work under the front of the car.

I would think spats in front of the front/rear tires would help a little bit with keeping the tires from churning up as much air. Which, in theory, would reduce lift created by the high pressure area in front of the tires as well as improve efficiency/top speed.

I would also expect tire "deflectors", which protect the wheel well from air attached to the front bumper and rear quarter, would have a marginal gains similar to above.

Spats would probably be pretty easy to rig up.

Some people have also played around with vortex generators on the back of the hardtop to keep air attached better. I seem to remember seeing a video where somebody did ribbon testing to show that it did have a positive effect.

 

This is what I mean by "deflectors"

 

In that pic, what's that black thing under the green bumper? Is that a factory part? I see a lot of cars with them, is it the same material as the bumper (ie, rubber rather than fiberglass)?

 

It's a GV lip. Lots of people around here have them or some Chinese copy. Those deflectors are designed to work with it since they are also made by Garage Vary.

 

I like the idea of using some flexible plastic attached to the fender as sort of a combo deflector/spat. Would keep the stock body lines the way they are and improve wheel well aero without too much work/money.

 

So far the plan is shaping up to be:
-some sort of tray up front (maybe this? NA Miata Aluminum Aero Undertray)
-an aluma-lite or abs tray in the rear to cover the hollow area under the rear bumper or just snip it
-wheel well deflector in the front, kind of like a reverse mud flap

Anyone know of a lip that doesn't have holes in it? I guess I could just block if off with duct tape or something. How about a cheap urethane lip?

Why doesn't anyone make a cheap urethane bumper for the miata that has the same ground clearance as stock + lip and also blocks off the airflow to the front tires?

edit: it's ******* hilarious looking at all these widebody kits that have plastic out for miles to either side.... BUT THEY DONT BLOCK AIRFLOW TO THE FRONT TIRE