Forbes reviews Fisker Karma

[srschrier]

Is the new Karma's fuel efficiency worse than a SUV?

http://www.forbes.com/sites/warrenme...e-than-an-suv/

[Rusty]

I'm not too excited about the editorial nature of this "review". Given his analysis method the Leaf gets 36 MPGe, and the Volt somewhat less. He's applying a "wells to wheel" analysis of electric cars in general, and then implicitly compares the result with EPA MPG ratings. He conveniently does so without a similar "wells to wheel" comparative analysis of gas burners.

Whether you accept his electric wells to wheel methodology or not, the debate style is somewhere between disingenuous and dishonest.

I wouldn't quote any of the conclusions of this "study" as worthy of merit.

Now if anyone can figure out how the Karma managed to get an EPA 52 MPGe, *that* would be interesting!

[Jason M. Hendler]

I am surprised Forbes would print such a non-sensical assessment of an actual product. I honestly can't follow what the author is trying to say about someone burning gasoline to make electricity - they do that in Hawaii, but not anywhere else in the US.

People were disappointed in the LEAF and the Volt when their EPA numbers came out, so no one should have been surprised by the disappointment expressed about the Fisker Karma's EPA numbers. That said, maniacal rants like the one posted are beyond reason.

If you believe for one minute that the application of Voltec and other similar technologies to larger or higher performance vehicles is going to yield much better results, then you are fooling yourself. GM and other automakers are waiting for battery tech to improve before attempting such vehicles. Even the Tesla Motors Model S is NOT going to hit the 135 mpge that the Roadster does, because the Roadster weighs half what the Model S (and Fisker Karma) does.

Until the energy / power density of batteries increases 2X - 3X, you will not have significantly better results in vehicles of similar size and performance.

[Jason M. Hendler]

Now if anyone can figure out how the Karma managed to get an EPA 52 MPGe, *that* would be interesting!

I am assuming the following:

- higher power demand from the batteries leads to higher power losses in a somewhat non-linear fashion, such that providing higher performance really hurt efficiency
- no question that the far greater mass of the Karma consumes a lot more power to accelerate, especially at a faster rate than the LEAF or Volt accelerates
- perhaps the Karma's regen efficiencies are poor, perhaps the greater mass regens too much power to slow it down quickly, and the battery pack can't absorb enough

Just pure conjecture - I have no numbers by which to compare, but these are the areas to look.

[N Riley]

Biased report not letting the truth get in the way. When you want to spin a report a certain way, you can do it simply by fictionalizing the facts.

[larry4pyro]

OK, so this writer doesn't like the way the EPA calculates MPGe. I guess his complaint is this number does not take into consideration the energy spent in generating the electricity - and he would be correct.

So he came up with his own calculations which results in the conclusion that the real energy usage is the EPA's MPGe times a derating factor of 0.365. That means according to his calculations the real energy use, sometimes called well-to-wheel of EV is only 36% of the EPA's MPGe.

But I don't understand how he can compare his well-to-wheel number for EVs against the simple MPG of a gas powered vehicle. In order to be a fair comparison he should look at the well-to-wheel numbers for both vehicle.

I don't know how accurate this writer's calculations are. Tesla released a Standford study, which appears to discount this writer's allegations.

http://www.stanford.edu/group/greend...slaReading.pdf

[Matt979]

Even if I am partial, that article is pure bullcrap. I could also come up with numbers that fit my view without effort, to bad that the EV has become so political.

For liberty and freedom we should all drive EV, imagine how much money would stay in the US and what we could save on reducing the effort we spend on securing all the oil deliveries, this money could then be invest in producing truly clean energy.

I guess the only way for the magazines to make money these days is to sell their opinions to the highest bidder. At least now we know that the OIL industry actually are really afraid, they are spending a lot of money on buying press.

[jsmay311]

I am assuming the following:

- higher power demand from the batteries leads to higher power losses in a somewhat non-linear fashion, such that providing higher performance really hurt efficiency
- no question that the far greater mass of the Karma consumes a lot more power to accelerate, especially at a faster rate than the LEAF or Volt accelerates

The EPA efficiency tests use uniform speeds and accelerations to ensure that they're comparing apples to apples. So while the Karma is capable of faster accelerations than the Volt/Leaf that would use more energy, that's not how the tests are done.

[Zod]

I think i lost a few IQ points while reading that garbage.

[Rusty]

The EPA efficiency tests use uniform speeds and accelerations to ensure that they're comparing apples to apples.

Thank you jsmay311. That was my recall as well, but I wasn't certain of it enough (without researching) it to post it. And I was certain I was too lazy to research it :- ).

Better yet, IIRC the EPA tests are done on a dynamometer. So cD and cross section need not apply, there's no wind drag. I don't know if they just run with the number, apply a fixed assumed wind drag rerating for speed, or apply the manufacturer supplied cDa.

Gives ya real confidence, doesn't it?