Anyone have any good experience with how MPG changes when the put on a Thule or some other roof pod? and what about the ever popular running boards, anyone know if they make much difference?

98 2500 burb W 454

 

Well think about it, you now have a huge bulge on top of your car that the wind is now hitting. Imagine the winds when cruising down the highway @ 70 mph...

Its the same reason it took another 200 hp to go from 258 to 268. Air at high speeds is like a wall... (Top Gear)

 

The general rule of thumb I've seen is that you're going to lose 10-15% mileage with one of those things on your roof. Besides, you're driving a big-block 3/4 ton burb - it's not exactly a mileage champ in the first place.

 

I am familiar with that, 8X the power to double the speed.
we mess around on occasion out on the bonneville salt flats, so we are aware of the monster. but in a practical "suburban" world, I'm not sure how much of that makes much measurable difference.

I don't have the formula with me, but it's dependant on Coefficent of drag (CD) Multiplied by Frontal area.

so if you take one of those luggage pods with 3 sq ft of frontal area, and it should have a very good CD - on a Prius, it is going to make measurable differences. But that same pod on a suburban, with maybe 40 - 45 ft of frontal area, and a CD of a gigantic brick, I'm not so sure whatever drag there was from the pod would not be lost in the noise and enormity of the Suburban numbers.

Thats why I am hoping someone has real experience and real numbers.