I've been checking around web sites and found a lot that says that spoilers in general lower gas mileage because you are adding more weight onto your car.Just kind of curious if this was true.l personally think it will not have an affect because the spoilers arelight.l think a passenger weighs more than the spoiler right?

It is not the weight of the spoiler itself that is the problem ( although it does not help either ). It is the increased aerodynamic drag that the spoiler creates that increases the fuel consumption.

Very few spoilers on production cars are actually designed to help with vehicle aerodynamics and high speed handling. A strong majority of them are just added for styling purposes.

l have a 08 scion xb and thought about getting it, will wait til have more dough. l think it will help .Without spoiler my XB without is getting 31.5 to 32 mph on hwy going 65mph. l also changed over to synthetic oil and put nitrogen in tires which alot of manufactuers are doing.

That is true. But the difference in gas mileage is very small and not noticeable.

Race cars have Carbon fiber spoilers to keep the weight down. And race cars need spoilers because they are so fast and they need more downforce from the spoiler so they do not go flying in the air.

nothing you will notice.

It will create a bit more drag, although who knows, it may help the xB, which is pretty much a non-aerodynamic box.although this year it got some curves. l do not think it will be noticed too much either way.

if the car is more aerodynamic it will be more likley to get better gas milage bec. the car will flow better in air as you drive. But since xB is not that well in aerodynamics.since its kinda box..lol
weight would not be a problem..u r correct on that.
its just aerodynamic change in cars body!!!
but the change is not really noticable.