[MetroMPG]

I think the answer is "it depends".

SAE may have a rule of thumb answer. (By the way, I thought aerohead has said 10 degrees for approach/departure angle?)

But sports car owners tolerate below average ride heights. They just have to watch out more for debris, bumps & driveway angles.

Makes me wonder what the lowest, non-adjustable OEM clearance is...

basjoos would probably tell you to make the low-hanging bits sacrificial. His pontoons are coroplast. Inexpensive and not a lot of work required to replace.