Can someone resolve this difference with Dave G’s results?

The lower the number, the more efficient the vehicle is. The Tesla Roadster, for example, is EPA rated at City: 32kW-hr/100 miles, Hwy: 33kW-hr/100miles. My Zero X motorcycle (full electric) averages 2kW-hr/100 miles in real world driving (7,000 miles street riding, so far, with zero maintenance). That means that my Zero X motorcycle is more than 16 times more efficient than a Tesla Roadster.

Here’s my best guess at the Chevy Volt EPA rating using power pack only, with the propsed 16 kW power pack and a 40 real world mile range. To maximize power pack life, using a lithium ion base, and being extra cautious, the power pack would never exceed 80% (also makes the recharging faster) and never go below 40% (real world indicates that a 20% to 100% range, managed extremely rigorously, would be possible with about the same power pack life span), which means thaht 40 miles would use 40% (80% minus 40%) of the power pack capacity (16kW).

Now consider that 100 miles is 2.5 times 40 miles.

The calculation: (16kW-hr times 40% times 2.5) divided by (40 miles times 2.5) = (16*0.40*2.5) kW-hr/ (40*2.5) miles = 16Kw-hr/100 miles

This means that the Chevy Volt, with a propsed curb weight 800 pounds heavier than the Tesla Roadster, using more conservative power pack management, would be twice as efficient than the Tesla Roadster, which I doubt. This tells me that GM is confident enough in the battery performance, after their extreme testing of two manufacturers, that they are using the most agressive power management possible (probably 20% to 100%, which equals 80% of power pack capacity), in which case the calculation becomes:

(16kW-hr times 80% times 2.5) divided by (40 miles times 2.5) = (16*0.80*2.5) kW-hr/ (40*2.5) miles = 32Kw-hr/100 miles

This matches the Tesla Roadster efficiency exactly, though the CHevy Volts looks to have a higher curb weight by 800 pounds. The difference – probably in improved battery performance from 2008 (the 2008 Tesla Roadster EPA ratings date) to 2010 expectations for the CHevy Volt release.

It wouldn’t surprise me if, based on this, that Tesla is already capable of getting below 30kW-hr/100 miles from their latest power packs, on the weight difference.

I think my work is reasonable based on the final results, but if someone else can improve on it, please chime in.

Note: This is the correct metric for series hybrids, such as the Chevy Volt. For parallel hybrids the gas fueled portion can be converted from miles per gallon to the new metric kW-hr/100 miles and each portion averaged, weighted by miles for a combined result of a single number in kW-hr/100 miles.

Dan Petit, Austin, TX

jap cars = good for environment
u.s. cars = bad bad bad

A more honest metric, however, would be $/100Miles, which would include the cost of electricity. Even more honest would be $/3years, which includes maintenance. But what people really want to know is purchase price + $/3years.

Regardless of the unit, the Volt and other PIHVs will look good.

Consumer will complain, word will get out, and sales will stagnate.

GM knows of bad public reputation and how quickly sales will stop ….corvair, vega, olds diesel, quad 4 , fiearo, turbo 200, Grand National Buick

The EPA looses any credibility by publishing a simple-minded number like “100 MPG” for the Volt, or any EV.

“Tits on a Bull” anyone?

The Volt is revolutionary technology, so it shows a revolutionary mpg rating. There is no reason this should lose it credibility. It really is more than twice as energy efficient as the Prius, and the numbers need to show that.

We (and the EPA) need to think out of the box, and come up with an mpg-evquivilent rating which is comparable with the mpg rating of gas cars, and captures the true energy usage based on the way the cars are actually driven by consumers.

I disagree.

If the goal is to sell the Volt primarily to the quantitatively oriented, the above formulation is ideal. These people will learn what AER means, it will be able to draw the inference, while still looking at the sticker, that they will not burn gas during the next 40 miles. Some of them will be aware that the electricity they do use will cost a lot less than gas. They will intuitively develop a blended average of battery and gas costs, and conclue that the Volt offers extraordinary energy economy.

While people who think this way dominate this board, they probably account for 1-2% of the population,

If the goal is to make the Volt a mass market car, the above formulation would be a problem. The public makes decisions with about as much mathematical rigor as Paris Hilton does. So faced wth a sticker that says:

40AER/ 50mpg

The typical consumer will say: 50 mpg? That is only 7 mpg better than the Prius, and it costs more. Plus you have to deal with plugging it in, I think I will just go with the Prius.

The way to really sell this is to develop an equivilent mpg rating that in one number, captures gas use, electricity use, electricy cost, and typical driving habits. That way, you will see

Volt 100 mpg
Prius 43 mpg

Gee, the Volt costs more, but you get 57 miles per gallon for your extra money. Do you have it in green?