Originally Posted by
LesterOfPuppets
I find this difficult to believe. I'd almost bet money we could get a vehicle at GVW of 120 lbs. to plane at a lower speed than I could with same vehicle with weight added to make a GVW of 360 lbs.
I believe that formula requires an "All other variables being equal, " as a preface.
The point of the formula is that the same tire on the same vehicle at the same weight will plane at a lower speed if it has lower pressure.
Hmm, no mention of tread, either. I found the formula you speak of, with a dead link to a NASA study. I'm intrigued...
Did some research on tires in college for auto and truck accidents in college, 30 years ago. As I recall the equation for hydroplaning in MPH was 10.6 x air pressure in PSI squared...which is very close to Shelton's posted equation. Lower air pressure increases the contact patch, which is like having two water skis instead of one....you can ski at slower speeds with 2 skis....same with car tires. We even tested it on a section of road that would have a 1/4 of water during mild rains....and it was spot on