Covering fog lights bumper corner
 

I have done some partial grill with great results. Will covering fog light flush with bumper cover using flexible transparent plastic improve further aerodynamics on my yaris?

improve further
 

Perhaps,but don't look for anything significant.That area is in an area of flow attack,so it tends to be held against the body simply from the favorable pressure gradient there.Also,the area 'behind' it is generously radiused,allowing the flow to easily round the corner to the body sides without separation.Any air trapped where the fog lights would be,simply pools there,with the outer,active flow just skimming off it, as though it were solid.

Aerohead, thank you for your detailed reply. I forgot to add that I covered factory fog cover with thin black sheet. The factory fog light had fins just for sport looking appearance and they trapped some air. I don't care that much about look.
What do you think about front or rear bumper aero tray?

My truck had recessed fog lights. I covered them with clear covers, but there was no detectable change in mileage.

I had another reason for covering them. The first time I really needed them, in a heavy snowstorm, they did not work because the recessed openings had filled with snow. I had hopes that smooth covers would work better in heavy snow. Unfortunately, the first heavy snow with the new covers was a heavy wet snow that stuck to everything, so the fog light were still useless.

That's why my conveyor belt air dam does not have fog lights. Edit: I see that I need a new profile photo with the new air dam.

I like what you did with your truck.

https://ecomodder.com/forum/member-j...ly+driver.html

bumper aero trays
 

I'm actually surprised that that Toyota didn't clean up the underside any better that that.This area would be a natural for paneling.(take a look under any Tesla you find)
With belly panels,a diffuser could be made to work.All that would show at the gas pump.Especially at highway speeds.

Another similar curiosity: the current Honda Civic has no paneling at the rear. None! One of the few cars left without any.

Another curiosity: The current Prius, similar to the Hyundai Ioniq and Kia Niro, uses a transverse-mounted muffler instead of a fairing at the back, with a panel to cover the gap to the rear bumper cover, as seen here:

http://www.thedetroitbureau.com/wp-c...-Underbody.jpg

This week while my car was in for a recall at the local dealer, I looked under some 2WD and AWD Prius parked next to each other and--surprise--the AWD uses a much smaller muffler, painted black(?), and no gap-filling panel. I wonder what series of managers' decisions led to that.