will a spoiler help my box??
 

i would like to add a spoiler to my box, especially if it may help my mileage...

i like 2 styles, stock style & "fab" style...which one do ya'll think would be the best choice??

BTW FTR mine currently does not have a spoiler at all

stock style
http://www.starrtrax.net/images/xbforsale/leftside.jpg
http://scionpartspeople.com/images/S...%20spoiler.jpg

"fab" style
http://www.magicdrift.com/images/pSc...W_Scion_xB.jpg
http://i24.photobucket.com/albums/c2...a/100_0751.jpg

For a roof extension to be of any help in reducing drag, it would need to be sloping downwards to help reduce the size of the wake. Since the OEM one acts as a parachute and forces air over the rear glass (for the purposes of keeping it clean), it won't help FE. The "Fab" style looks more cosmetic than functional.

As a fellow xB owner I say go for the Fab wing, I have one too ...

I will never know what the impact is to your mpg's, but I will tell you that adjusting the nut behind the wheel will compensate for any particular hit you take for looking cool ..lol

Besides, I know you didn't buy the box for its aerodynamics ..

well this nut has already been adjusted...i get typically 4 more mpg per tank when i drive calm, versus getting to work in record time

box
 

van type vehicles do not suffer separation as notchback or fastback cars and consequently do not generate lift as the other cars do,so spoilers are of no value unless perhaps you were driving at extra-legal speed on wet roads.
As far as drag reduction,I've never seen a test in which a spoiler helped.
The xB is a 'full-wake' vehicle.It's wake is as large as it's frontal area,as there is little if any roof or body sides camber.
It's my opinion that only something like a boat tail extension would give measurable relief at the pump.