This true at any constant speed, and one of the great things about the GE Fit is the instantaneous mileage gauge (that blue bar at the bottom of the display). If you pay attention, it's a great educational tool for your right foot. Just don't pay so much attention that you get distracted.

 

or get a numb/sleepy foot, haha

 

Calculated rpm @ 70mph = 3416, based on 872 rev/mile, per Tire Rack website for the OE tire. There are two things at work here. Aero drag, which was already mentioned goes up with the square of speed. The other thing, lesser known, is that most gasoline engines are most efficient running at peak torque, which is 4800 rpm in the case of the Fit. I know, pumping losses are smallest at WOT, but with Vetec, thats much less of a factor. Overall efficiency is what I am talking about.

Back in the days of large displacement, slow turning American engines, peak torque was usually around 2000rpm. My V-6 Chevy truck had an overall gear ratio of of 3.42 x .7 and 225/75R15 tires. That resulted in 1909rpm @ 60mph. It got great mileage for what it was, up to 23 mpg.

The BMW 325i 5-speed close ratio (no overdrive) was 3000 rpm at 70mph but managed 30 mpg highway.

 

[quote=nikita;851593]Calculated rpm @ 70mph = 3416, based on 872 rev/mile, per Tire Rack website for the OE tire. There are two things at work here. Aero drag, which was already mentioned goes up with the square of speed.
The other thing, lesser known, is that most gasoline engines are most efficient running at peak torque, which is 4800 rpm in the case of the Fit.

Unfortunately thats not correct. The minimum on the fuel efficiency curve is related to a lot of things like BMEP, but not torque. It can be assumed easily that if torque is maximized there must be more fuel consumed then.

 

Fuel burn is based on power not directly on torque alone. Peak hp will be peak fuel burn. Without a way of directly measuring BMEP, like the old propeller airliners had, its the best we have. Its just that the torque peak usually comes close to best efficiency, unless the computer is adjusting mixture and timing way off.

 

Dozens of dyno curves and fuel consumption say otherwise unlerss your 'close is within a thousand rpm.
hp = torque x rpm/5250
Rarely, if at all, will minimum fuel consumption be anywhere near torque peak and rpm; its pretty much at some lower hp and rpm than max anywhere on the curve, i.e. part-throttle.

 

I looked up some detail on Honda's Vtec system and it looks like the torque curve is "unusual". It actually has two peaks. I suspect the lower rpm one is near where most efficient cruise would be if Honda geared the car that way. I was referring to the type of torque curves common in older low-performance engines. My Ford pickups had one very distinct peak at about 2500, the Chevy a flatter one peaking at a diesel-like 1900.

So, newer tech has changed things. What final drive gearing do you think a Fit can actually pull without having to downshift for a slight rise or headwind? Honda engineers were flat wrong seems to be the general feeling. Ford was wrong in the other direction. That F-150 had 3.31's and a .7 OD. With stock tires, it was way below peak torque at 65 and felt like it. Gas mileage was relatively bad compared to the otherwise similar Chevy it replaced.