Rear Window Lip or Trunk Lip vs FE

[jayliu1984]

Hi guys, I have a 4-door sedan that IMO would benefit a lot in the "looking" deparment by having either a rear window lip or a trunk lip.

Since I drive city most the time, I don't expect they will affect FE much. But I am courious if I dirve highway, do those things positively affect FE or adversely?

[RiderofBikes]

as much information i have gathered lurking myself, your not doing excessive highway driving in any stint, or going above 45mph for most of your travels then a spoiler probaly wont have any effect. A Lip of some sort would be a tad more beneficial than a wing especially if its a raised wing of a sort for highway driving aspect. Of course not knowing what kinda car this pertains too, my input is a bit moot.