Drag and rolling resistance formula
I stumbled across this formula and thought there might be others on here that might find it interesting. Drag and rolling resistance formula.
Forum Discussion
wilber1 wrote:
.34 is the CD of a Camaro. Looking at CD's for 1500's, our HD's should be .5 or more and with a barn door fiver behind .8 might even be conservative.
What you're saying sounds reasonable at first but, if the coefficient of drag were .8 it would be impossible to get better than about 7 mpg driving 60 mph pulling a big 5th wheel. Because we generally get about 10 mpg and we know our diesel engines can't achieve an efficiency beyond 40% nor can the drivetrain efficiency be any more than 85% the very highest value that seems to make sense for the CD is .47.
With a CD of 4.7 for my RV I could still get 10 mpg towing at 60 mph yet at 120 mph I would be needing 605 HP and be getting 3.4 mpg.
According to the formula, the HP required to overcome drag at 120 mph with my RV, assuming a CD of .47, is 531HP and the HP required to overcome drag in a Camaro at 120 mph with a CD value of .34 is 88 HP. This sounds reasonable.
