I always put it on Sport mode. I wish there was a way to set it as a default. I prefer the stiffer wheel feel in sport. I actually installed the Dinan software because I thought it made the car always on Sport. It turns out the Dinan software only makes the normal mode "Sportier" and you still need to engage sport to get the full effect. I don't think Sport changes your fuel economy only the speed with which the throttle butterflies open with respect to the throttle pedal position