[aerohead]

Originally Posted by Phase

https://www.trdparts.jp/english/prod...aero_ver1.html

any thoughts on toyota themselves using side skirts as an aero add on to improve mpg? there cfd even shows light/mild ones helping

check the link

Are you talking about the glue-on rocker panel extensions from TRD?
If so, that's 1982 technology, Pontiac Division of General Motors applied to their next generation Firebird Trans Am. Something like a 4-count drag reduction.
Cardboard and duct tape would tell you what they'd do for you on the IONIQ.
I did it to Spindletop, SPIRIT, and Baby.
The belly pan runs flush to their bottom. All the way around the vehicle, including the diffuser.
I'm surprised Hyundai hasn't done that already.