Best technique when driving in strong head/tailwinds

[brucepick]

I'm with ombwtfbyobbq, who wrote "same as always, as slow as possible in top gear."

But if you want to have a higher speed and a lower one to optimize things at an average speed, drive slower against the wind and faster when you're with the wind. Because the "wind resistance penalty" goes up much faster than your speed does. When the wind is with you, you are spared that extra load on the engine, which is more than you might guess at first.

The resistance actually goes up with the cube of the speed change. What that means in practical terms is that the penalty for increased speed is considerable. Here are some calculations using 40 mph as a base value.

40 mph: drag = base value
50 mph: drag = base x 1.953
Which means that the air resistance that you are fighting at 50 mph is essentially DOUBLE what you had at 40 mph. But your speed is only increased x 1.25, so you're really losing ground on that score. You are creating your own resistance that you have to fight against.

60 mph: drag = base x 3.375 but your speed is only x 1.5 the base speed
70 mph: Drag = base x 5.359
80 mph: drag = base x 8.000 but your speed is only x 2 the base speed

So if you needed 5 hp to overcome wind resistance at 40 mph, you need 5 hp x 8 = 40 hp to overcome it at 80 mph. Those 40 hp will cost you a lot of fuel.

Of course a more aerodynamic body like an Insight will give you less resistance at any given speed, but whatever resistance there is goes up by the same cube-based percentage.

[Lug_Nut]

Originally Posted by brucepick

The resistance actually goes up with the cube of the speed change.

Are you sure? That's what I get for being stoned during High School Physics in the 70's (D-, and that was a gift from the teacher).
Yeah, E=M*C2, not M*C3. Energy goes up with the square, resistance goes up with the cube...

[brucepick]

Originally Posted by Lug_Nut

Are you sure? That's what I get for being stoned during High School Physics in the 70's (D-, and that was a gift from the teacher).
Yeah, E=M*C2, not M*C3. Energy goes up with the square, resistance goes up with the cube...

Actually I got that gem from another site populated by brainiacs. I believe the guy. And the cube thing makes sense. Road speed is linear (not even squared like area would be). But the air you compress in front of you is a three-dimensional blob. The faster you go the further forward that "blob" of compressed air extends. The volume of the blob and your pressure against it are all volume-based, that is, the dimension is cubed.

And the bottom line is, speed kills your fuel economy. Increasing your speed 25% just about doubles the air resistance. That's from 40 mph to 50 mph. Increase another 25% to 62.5 mph and you double it again, so it's now four times what it was at 40 mph. But you've only got your speed up to 62.5 mph!

Every 5 or 10 mph you can reduce your speed, you're saving gas. As long as you can run the car in top gear without lugging the engine or other such issues.