This is such a timely topic. I actually just changed my driving habits a few weeks ago as well and using my onboard computer (measures AVG MPG, current MPG, etc), I have noticed a decent improvement. I used to get 19-20 MPG, but here are my numbers so far when driving between 65-70 mph:
In 2 fuel fillups, I’ve gotten:
1st: 23.9 MPG (no aircon, about 30 psi tire pressure)
2nd: 22.2 MPG (lots of aircon the past week, raised tire pressure to 34 psi midway)
I’ve read that using your aircon doesn’t matter too much when compared with an open window due to aerodynamic drag.
My 3rd fuel up should be interesting with no aircon and the higher tire pressure.
One good unintended thing with driving slow is it decreases road stress since people can pass me all they want and I don’t get as annoyed now.
