Undertray in 1969-70 Technical Forum Posted October 10 · Report reply I don't this guy tossing out any actual qualifications other than he authored a book and stood in front of a camera. Plus I might be inclined to give him a tad bit of credit if his personal cars weren't a generation one Prius and a Honda Insight. Jeremy Clarkson once spoke of the Insight as wanting to crash it into a tree just so he wouldn't have to drive it anymore. That and in the one video he claims he wasn't aware of how the curve at the front of "undertrays" had and aero effect. Reading between the lines this tells me this boob has absolutely no qualifications in the field of aerodynamics. Just no way. But as the saying goes "Just because the biggest fool in the world says the sun id shining doesn't make it dark outside." I long since have been quite distracted but about 15 years ago I stocked up on some PVC sheet to do essentially the same sort of things. It and the car are still out there but I'm still quite distracted. Though it may not be clear on every video, allowances are to be made to vent air from underhood. A side effect he mentions of all this that the air directed under the car this way has a bit of venturi effect and will draw that warm out through smaller openings than one might expect. If you do things right. Do a big lower like he shows on his Prius on a Fox Mustang and you will have an overheated engine PDQ. Because those cars draw the air for the radiator from up under the front bumper. I bet he has no clue about that. Aero stuff isn't a one size fits all science. For what little I know about it anyway. Far from an expert me, but I've tried to listen while smart people talked.