[joedoh]

140? its not probable. wind load goes exponential and makes a big difference over about 60mph, and these have a lot of upright surfaces and even more "wetted area".

I had a pretty boxy older BMW with plenty of grunt and a tall gear and it topped out speed at around 123. that doesnt sound a lot more than the 114 1project mentions but you have to realize that the wind load difference (the resisting force the vehicle pushes against) in that 9mph was a lot more.

and I dont mean to say that wind load isnt exponential below 60mph, it is, thats actually the "squared" part of "velocity squared", just that for anything resembling a car it doesnt start getting to be a huge number till after about 60mph.

for example, say the wetted area A is 24 ft (total guess) and the coefficient of drag Cd is 0.45 (its probably not even that good) and the wind pressure of air is (0.0256*V^2), at 30mph the force the truck would need to push would be 24*(0.00256*30^2)= 24lbs, 60mph the force would be 24*(0.00256*60^2)*0.45 = 100lbs, at 114mph it would be 359 lbs, at 123 it would be 418lbs. so even though you are only traveling about 4 times as fast as 30mph the wind load is 17 times as high at 120mph, 4 times as much at 120 vs 60mph even though only twice as fast. even that 9mph difference, the load goes up as much as it did from 30-60.

this is why your top speed is not redline rpm x top gear, you run out of torque much sooner than rpm from pushing wind. its also why you can get better mpg by slowing down, pushing wind doesnt save you a penny.

cliff notes: going really fast in a brick takes a lot of torque