Page 1 of 3

highway speed efficiency

Posted: Tue Sep 11, 2012 4:09 pm
by adric22
As any Leaf driver will tell you, if you hop on the highway and hit 65-75 mph, your range drops nearly in half. I've noticed after driving the Volt for a while that the highway doesn't really seem to affect it nearly as much. I seem to get 40 miles in town or 40 miles on the highway.

So the question is, why? Is it a matter of aerodynamics? Or is there something about the Leaf drivetrain that makes it inefficient at those speeds? I remember reading something about Tesla having to make modifications to the model-S to improve high speed efficiency. The Volt's drivetrain is considerably more complicated to include the I.C.E., however I believe I read somewhere that it does use both of the electric motors at times even when the I.C.E. is powered down. Is that the key?

I was just thinking if the Leaf could improve the highway efficiency where one could reliably get 80 or more miles per charge on the highway that would actually make a pretty big difference in the acceptance in the USA market.

Re: highway speed efficiency

Posted: Tue Sep 11, 2012 4:19 pm
by DaveinOlyWA
did not want to mention this before in fear of being egged, booed or even worse, not invited to the Christmas party...

but i have to say the Volt Owners probably know much less about how their cars work than they think.

first off, we have a battery where just over half gets used so what is the rest doing? and how much of that is left? who knows?? the Volt might be suffering degradation at double the rate of the worst AZ LEAF.

ok, maybe that is a stretch, but no more of a stretch to think that going 20 mph faster wont hurt your range whether it be battery or gas.

so i am guessing the actual percentage of the Volts battery being used at any one time is variable and remember, its just speculation

Re: highway speed efficiency

Posted: Tue Sep 11, 2012 4:35 pm
by palmermd
if you change your speed from 55mph to 65mph you will lose about 20% of the efficiency. In almost any vehicle. In a Leaf 55mph gives you a range of 88 and speeding up to 65 drops it to about 75 (on a new car with full capacity). Same thing for a gasoline car. My friend was getting 17mpg in his truck commuting at 65. I asked him to try 55 for one week and guess what..he came back with 21mpg...a 20% improvement.

The difference is that the more efficient the vehicle, the bigger the change (same percentage). In a Prius at 55mph you get about 55mpg, and jumping to 65 lowers it to 45mpg. That is a 10mpg difference. Leaf is equivalent to a 20mpg difference, and very noticeable because we have equivalent to a one gallon gas tank in the car.

The Volt is a 40mpg car so that puts the changes just shy of the Prius numbers. I don't know the specifics of the Volt, but I'd assume that you get 40 miles range at 55 mph, and that would mean that you get about 33 miles at 65. It is only a 7 mile difference because it is such a small "tank".

Re: highway speed efficiency

Posted: Tue Sep 11, 2012 5:12 pm
by cwerdna
palmermd wrote: The difference is that the more efficient the vehicle, the bigger the change (same percentage). In a Prius at 55mph you get about 55mpg, and jumping to 65 lowers it to 45mpg. That is a 10mpg difference. Leaf is equivalent to a 20mpg difference, and very noticeable because we have equivalent to a one gallon gas tank in the car.
Related to the above was a concept I kept ignoring until I found the article that I posted at http://priuschat.com/threads/car-and-dr ... nts.95536/" onclick="window.open(this.href);return false; regarding how we should be measuring "gallonage" and the bad math (in a Consumer Reports test) that http://ecomodder.com/forum/showthread.p ... 10091.html" onclick="window.open(this.href);return false; pointed out.

The "small" drop in mpg that the V8 Mercury Mountaineer (from 23.8 to 17.8 mpg) as a result of going from 55 to 75 mph actually resulted in a FAR greater delta in "gallonage" than the "large(st)" drop made by the Insight when it went from 51.9 mpg to 36.5 mpg.

Over 100 miles, the Insight with it's "large" drop would use 0.81 gallons more when going 75. The "small" drop Mountaineer would consume 1.42 gallons more.

Re: highway speed efficiency

Posted: Tue Sep 11, 2012 5:33 pm
by Herm
adric22 wrote:As any Leaf driver will tell you, if you hop on the highway and hit 65-75 mph, your range drops nearly in half. I've noticed after driving the Volt for a while that the highway doesn't really seem to affect it nearly as much. I seem to get 40 miles in town or 40 miles on the highway.
The GOM in the Leaf is notorious..

Re: highway speed efficiency

Posted: Tue Sep 11, 2012 9:36 pm
by mxp
For all it's worth, today I charged up to 80% (Sorry, I forget how many bars) and did a 40 mile trip at 75mph (80mph at times) mostly and ended up with 3 bars left. Eco mode all the way.

Nowadays, I don't even bother to look at the guess-o-meter. ;-)

Re: highway speed efficiency

Posted: Tue Sep 11, 2012 10:13 pm
by LEAFfan
adric22 wrote:As any Leaf driver will tell you, if you hop on the highway and hit 65-75 mph, your range drops nearly in half.
This is absolutely not true. There's a BIG difference between 65 and 75. I could go a steady 65mph and still get close to 4m/kW h (3.8 X 21=80 miles). That's not even close to a 50% drop. Even at 75mph, I could get more than 3m/kW h (3.2 X 21=67 miles) and that's still not even close to a 50% drop.
I always wonder why some people like to exaggerate to try to make their point. It never works. Just be truthful and let the chips fall where they may.

Re: highway speed efficiency

Posted: Tue Sep 11, 2012 10:37 pm
by Nekota
LEAFfan wrote:
adric22 wrote:As any Leaf driver will tell you, if you hop on the highway and hit 65-75 mph, your range drops nearly in half.
This is absolutely not true. There's a BIG difference between 65 and 75. I could go a steady 65mph and still get close to 4m/kW h (3.8 X 21=80 miles). That's not even close to a 50% drop. Even at 75mph, I could get more than 3m/kW h (3.2 X 21=67 miles) and that's still not even close to a 50% drop.
I always wonder why some people like to exaggerate to try to make their point. It never works. Just be truthful and let the chips fall where they may.
Or since the primary loss is the square of the speed (75*75) / (65*65) is 1.33 or 33% increase or (65*65)/(75*75) is 0.75 or 25% decrease.

Re: highway speed efficiency

Posted: Wed Sep 12, 2012 5:52 am
by Pipcecil
As a leaf and a volt owner I can say that the volt in all EV mode, handles the highway speeds significantly better than the leaf. I attribute this a lot to aerodynamic efficiency. The leaf is a larger vehicle, so it will create more drag than the volt. In addition the volt has a very low ground clearnance - my wife scraps bottom every day leaving the driveway. She never had before even when she owned a two-seater sports car. The lower profile is a big aerodynamic saver at high speeds, which is why tesla has the air suspension thingie that lowers the vehicle at high speeds and semi trucks us that plastic paneling to cover up under the trailers.

Those two together I think make a good difference. As for the powertrain, I still think the leaf's is more efficient (i.e. see the EPA's MPGe, 94 vs 99). The higher your speed, the less effiecient (exponential) really points to the aerodynamics of the car.

Re: highway speed efficiency

Posted: Wed Sep 12, 2012 6:35 am
by ksnogas2112
Herm wrote:
The GOM in the Leaf is notorious..

Sounds like a new rapper name, The Notorius G O M

<insert chuckle>

:lol: