[pdexta]

After a recent change in my daily commute I've seen my gas mileage drop ~5mpg (from 40ish to 35ish). The new commute puts me on the interstate for the majority of my drive, typically around 80mph.

My '01 Civic Ex is geared very short. At 80mph I'm right at 4000rpms. There appear to be several other transmissions available to bring the RPMS down. An LX/DX tranny should run 3500rpms @ 80 and a HX tranny should run 2700rpms @ 80.

I've tried searching, but haven't had much luck finding results to a change in gearing. Do you feel like longer gears would significantly improve mileage (enough to bring it back up to what it was before?) or at those speeds is wind resistance simply going to kill mileage regardless of cruising rpm?