Can anyone tell me what difference in gas mileage a tonneau cover would make. Also is Extang a good brand of cover?

 

A tonneau cover has little affect on fuel economy. Some old wife must have started that tale.

I can't speak to the quality of Extang products, so rather than feed you a line, I'll defer to someone who knows.

 

I'd have to differ from mazz on this one to some degree. The tonneau does have a small effect on the mileage, provided you have the tailgate up all the time, and at highway speeds, but isn't a huge difference like some claim. The biggest thing is the bed is covered and that eliminates a whole bunch of turbulence in the bed. This makes the truck have one less vibration through a smoother air flow line. Good luck.

 

I have an Undercover (hard cover) and have seen maybe 1/2 mile per gallon. The Ram is pretty aerodynamic already. I think the soft cover may actually increase drag. There is a web site that has done some aerodynamic testing of the Gen III Ram and their tests proved tailgate up was better than down and better than the net.

Fords do get better mileage apparently with a hard cover.

 

I have a 2003 HEMI quad cab SB. I started out with the OEM plastic bed liner and tail gate always up. I then switched to a WOLF soft tonaue cover. Just like EXTANG (which is a very good cover by the way) mine has an easy to disasemble aluminum frame and gas shocks for lift asist. It might have helped gas mileage maybe .3 or .4 MPG but that's about it. It was a bit loud as it flaps in the wind some at highway speeds no matter how good the fit is. There was no noticable ride improvement. I then bought an A.R.E. Z series truck cap. It easily added another 1.5 MPG over what I was getting with the wolf cover (a gain of 1.7 or 1.8 from stock). The truck is much more quiet at highway speeds now due to the significantly improved aerodynamics provided by the cab level cap and the ride is FAR FAR better then stock since the weight of the cap "loads" the rear suspension. A benefit I didn't consider when purchasing the cap but am greatly happy about since I do a good bit of driving. I haven't tried a hard tonaue cover but I imagine it would produce results somewhere inbetween. Pickup trucks just aren't aerodynamic.. period. They flow threw the air about as well as a brick floats. A great deal of wind drag actually occurs underneith the truck. I think manufactures could do more to try to reduce the under drag of trucks... just my .02