Revised gearing for highway commuters?

[nader]

I haven't been able to find the spec on final drive ratio, but i was thinking it might be interesting to have a new ring and pinion cut to lower RPMs at highway speeds. I know wind resitance becomes a bigger issue but I cant help but think that lowering RPMs at highway speeds by 15-20% will increase range. Of course acceleration will suffer but i think its got enough torque that it won't make that much of a diffefence.

Thoughts?

[TomT]

Unlike on an ICE vehicle, it wouldn't make much difference.

I haven't been able to find the spec on final drive ratio, but i was thinking it might be interesting to have a new ring and pinion cut to lower RPMs at highway speeds. I know wind resitance becomes a bigger issue but I cant help but think that lowering RPMs at highway speeds by 15-20% will increase range. Of course acceleration will suffer but i think its got enough torque that it won't make that much of a diffefence.

Thoughts?

[edatoakrun]

About the only significant difference, I expect, would be a higher top speed-on a downgrade.

I was going to suggest, that a far cheaper and easily reversible way to test this, would be to get higher-profile tires, to lower freeway RPM.

But that got me wondering about aerodynamic drag. Normally a higher profile tire would, by raising a car, very significantly increase drag. But with the LEAF's smooth underbelly, it might not increase drag a great deal (though increased lift might significantly affect handling if you changed the final drive ratio enough, AND found a grade steep enough to produce very high speeds...).

I owned a Citroen DS21 with an (almost) smooth belly plate, and a hydro pneumatic adjustable suspension, giving it several inches of ride-height adjustment. I don't recall ever driving long distance on the high setting, to check for how much fuel economy or top speed was reduced, though...

[palmermd]

Unlike on an ICE vehicle, it wouldn't make much difference.

+1 it might actually be the opposite. Many times there is a high rpm point where the motor will drop off rapidly in its abitlity to put out power, and the efficiency at that point seems to go up just a little, but for the most part it makes little difference what speed your are running. You'd have to get the motor curves to know.

[Herm]

it would not make a difference, the Leaf's motor has top efficiency over a wide range of RPM. Going to a narrower 185 size tire may reduce your tire drag, also lowering the car should reduced air drag. You should also inflate the tires to the max sidewall ratings.

[DaveEV]

+1 it might actually be the opposite. Many times there is a high rpm point where the motor will drop off rapidly in its abitlity to put out power, and the efficiency at that point seems to go up just a little, but for the most part it makes little difference what speed your are running. You'd have to get the motor curves to know.

The motor curves are published somewhere by an engineering publication - can't find the link right now, but there's a thread somewhere.

Efficiency is at it's peak of appx 95% at load (a bit more than very light throttle) and moderate speed (between 55 mph or so). Efficiency drops to 85% outside of that sweet spot. Note that this doesn't take into account other losses - such as the motor controller or battery losses at higher currents.

Edit: Here's the link to the thread: Nissan LEAF featured in Feb '11 SAE Newsletter and a quick screengrab of the chart.

[ENIAC]

I haven't been able to find the spec on final drive ratio

The LEAFs final drive ratio 7.9377

[edatoakrun]

Doesn't look to me like you'll gain much at (legal) freeway speeds by changing the final drive ratio, and would also lose efficiency in low-speed use. But, unless I'm missing something, looking at that efficiency curve, I cant help thinking that The LEAF's overall efficiency could be improved-a few percent overall?-by a variable final drive ratio, even as simple as two "speeds".

Obviously, Nissan decided cost and complexity outweigh benefits on the LEAF. I wonder if Nissan is considering it, though, for future higher cost and performance cars, such as the ESFLOW based on the LEAF drive-train?

[Herm]

But, unless I'm missing something, looking at that efficiency curve, I cant help thinking that The LEAF's overall efficiency could be improved-a few percent overall?-by a variable final drive ratio, even as simple as two "speeds".

Are we looking at the same graph?.. there is a possibility of improving eff below 40mph, but little power is consumed at those slow speeds anyways, it may gain you about 1/10 mile range if you drove at 30mph (that was a WAG).. it is already optimized for speeds from 40-80mph with its single speed transmission.

[derkraut]

I would imagine that Nissan tried all the stuff you guys are talking about, when they developed/tested the Leaf.