yahoo.com often speak of the best fuel efficient is driving around 55 mph. i find that misleading.

for example..............for a stick shift, 55mph on 3rd (at 5000 rpm) gear is a gas eating compare to 55mph on a 5th gear (2700rpm).... sigh if only we have a 6th gear, the 55mph mark will run at about 1900 rpm instead of 2700 rpm.

they should focus it's not the speed, but your engine's RPM that determines your fuel efficiency instead the speed.

 

In the automatic tC, 55mph would keep the car at around the 2000rpm range in 4th gear. If remember correctly, 65mph is in the 2500rpm range in 4th gear. For me, I don't think driving at 55mph would make much of a difference. Not only that, I always drive at 65mph on the highways and people probably already think I'm a fool for doing so, going 55mph would probably just make think I'm stupid or something. Driving at 65mph on the highway mixed with city driving, i average about 28-29mpg.

 

You should read my thread that I posted last year. 36Mpg in my 5-speed tC, cruising at 55-60mph. It's sad that our gearing is ____ poor for fuel mileage. If you have a few thousand burning a hole in your pocket, there is a shop in PA that is swapping our 5-speed 1st gen transmissions with 2nd gen 6-speeds.

Anyway, here is the thread: https://www.scionlife.com/forums/sho...d.php?t=188095

 

Speed is a more important factor in determining gas mileage. If your engine is holding at 2500 RPM in 1st gear you would be getting terrible gas mileage due to your low speed. If the engine was holding at the same RPM in 5th gear (or your highest gear, whatever it may be), your gas mileage would be significantly better because you would be going much faster.

An easy way to think of it is that maximum fuel economy is going to be obtained at the lowest speed you can go in your highest gear without stalling the engine. There are more accurate and complicated ways to determine it though.