I drive a canadian 2005 Civic SI sedan and was wondering how fast i should drive for best fuel efficiency. Usually i follow the speed of traffic in the fast lane reaching around 75 mph, but should i not be driving that fast in a civic?

 

Well im not too familiar with your model of civic, but take a look at you tach and se what rpms youre turning at that speed. In my 97 at that fast im turning abuot 3.5k rpm which i know kills my mpg. I can reach almost 40 mpg when i average around 60 mph without much city driving.

 

Sometine I did an experiment for a month. Driving 5 or 10 MPG under the speed limit. It helped me to save some gas and achieve better fuel efficiency.

 

If you can do around 55mph, you're probably in the sweet spot for gas mileage. Above that speed, the wind resistance starts multiplying exponentially, and your car has to work a lot harder just to overcome the wind resistance at 70 than it does at 60. Above 55mph, here's how your efficiency calculates (on average):

- 3% less efficient at 60 mph
- 8% less efficient at 65 mph
- 17% less efficient at 70 mph
- 23% less efficient at 75 mph
- 28% less efficient at 80 mph

So by you doing 75mph, you're already using 23% more gas than you would if you'd have stayed in the slow lane which, on your car, is something like 10mpg.