Quote:
Originally Posted by oldtamiyaphile
If we're talking about NA engines, you're best off with a 3 speed, assuming the same rollout.
Skip shifting 1-3-5 has the effect of increasing the average load on the engine for reduced pumping losses, remembering that BSFC is over 3k rpm for most engines anyway. I skip shift my NA's unless towing/ hill/ need the acceleration.
My best tank ever was recorded skip shifting, if nothing else it reduces clutch and shift linkage wear.
The term 'overdrive' is meaningless. Various cars in the 90's had double overdrive five speeds. A lot of cars today have triple over drive.
Less gears= less friction
Don't be fooled by today's 10 speed autos. They're more about the driver not noticing when the computer shifts the wrong way and less about economy.
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The Insight's 1.0L delivers best economy between 1750 and maybe 2250RPM, with 1500 to 2500 still delivering "reasonably good" economy. In practice, when I accelerate at high load up to 3K RPM there are noticeable economy losses. Taking it up to 3-4k on a highway on-ramp might drop a trip with 10 miles of cruising afterward from ~95mpg down to 75-65mpg, when compared with keeping it below ~2250 when getting up to speed.
In order to get a highway cruising RPM of ~2000, the gear ratios are so wide that you're going both above and below this range, and the tiny 1L doesn't have the torque to climb some steeper hills even in 2nd gear once the battery is depleted, so moving all of them up isn't an option.
Another gear in the middle would definitely improve economy when accelerating, and give more options when climbing hills. As-is, in 5th gear I can only maintain lean-burn on nearly level ground. Any hill I can't climb in 5th, I generally can't in 4th either; I imagine 4th would be more useful in an area with longer, more rolling hills. 3rd is often too far in the other direction and I end up with low-load, high-RPM when climbing hills - 3rd is a good passing gear.
I'll grant that an extra gear would add friction. I'm not sure how much of a real-world effect this would have. I'd guess that Honda put a 5 speed in this car more to save weight though - the gearbox only weighs ~57lbs.
EDIT: Here are my available gear choices if I want to stay at peak BSFC. Going outside of the range basically prevents me from getting 90+ mpg trips:
Could definitely use another gear in the 1-2-3 range.