Ford Chassis

[nothermark]

I think you have it. I forget where it crosses over but by the time we get those boxes up into the 55 + mph range the biggest problem is pushing the air out of the way. That way with a lot more slippery vehicles too.

[jharrell]

Originally Posted by nothermark

I think you have it. I forget where it crosses over but by the time we get those boxes up into the 55 + mph range the biggest problem is pushing the air out of the way. That way with a lot more slippery vehicles too.

Yeah just running some numbers through a online calculator seems to confirm it, drag coefficient and frontal area have the biggest effects in the 65mph range, weight less so.

You can mess with them here and see, I made some educated guesses on engine efficiency and drag coefficient:

Aerodynamic & rolling resistance, power & MPG calculator

Looks to be about an 80/20 split on air vs rolling resistance at highway speeds.