Tiny difference, between the sport and the base automatic (37 and 38 highway), but I am still curious as to why. Could it be the "aero" stuff creats that much more drag?

 

Maybe slightly different programming in the auto tranny with paddle shifting?

 

the sport weighs more because of the extra body parts....spoiler, sideskirts, front faschia, fog lights, etc

 

I think your right!! The extra weight is always there.

 

The larger tires create more frictional loses and change the gearing to a higher ratio may be just enough to bog it a hair. bigger tires always mean less mileage.

 

Cause Sport goes faster!

 

But the MT sport also has bigger tires and more weight, and its mileage does not change.

 

I just like this answer the best lol

 

That's my guess.

 

I wonder what's the fuel economy like for the Sport AT if you only drive in the sport mode...would it be better than the rated MPG? I would think so, if the driver is good at switching gears in the right situation to save gas.

Somebody that has a Sport AT should try this out!