We've had a ride in a prototype 2012 Tesla Model S electric luxury sport sedan, and it was impressive.

The car was smooth, quiet, and relatively fast at speeds up to 95 mph on the test track surrounding Tesla's assembly plant in Fremont, Cailfornia.

Intrepid test driver (and Lotus racer) Joe Nuxoll didn't take his foot off the accelerator at 55 mph, and neither will buyers of the first Model S cars--which are scheduled to roll off the lines this summer.

Which is why we're a bit concerned that the ranges announced by Tesla for the Model S--160 miles for the $57,400 model, 230 miles for the $67,400 version, and 300 miles for the $77,400 trim level--are derived from at an average speed of just 55 mph.

That's according to Tesla CEO Elon Musk, who said at the Geneva Motor Show earlier this week--as noted by our reporter Antony Ingram at the show--that the company's range data assumed "an average speed of 55 mph."

80 mph on I-5

Many of the early Model S sedans will be sold in California, and Tesla has made a point out saying it plans to install a "SuperCharger" network of ultra-fast DC fast charging stations along the route between San Francisco and Los Angeles.

That would allow Model S drivers whose cars are fitted with fast-charging capability to refill much of their pack in less than an hour, pausing for a meal or a scan of their digital devices while the car recharges.

But the main route between the two California cities is Interstate 5, where almost no one drives 55 mph--or even complies with the speed limit.

On the long straight stretches through the Central Valley, most traffic moves at 75 to 80 mph. And we see no reason why Tesla's weatlhy, accomplished buyers wouldn't do the same.

Uncrunched numbers

We reached out to Tesla, asking the company to provide us with the ranges of their various models at the more likely intercity speed of 75 mph.

2012 Tesla Model S Charging Connector

2012 Tesla Model S Charging Connector

Spokesperson Khobi Brooklyn wrote back, "We haven't crunched those numbers yet," and didn't respond to our subsequent request that Tesla do so.

We worry about this because Nissan quoted 100 miles for the Leaf range before launch, then ended up with an EPA rating of 73 miles--and took heat for it. Similarly, GM quoted 40 miles as the Chevy Volt's electric range, only to receive an EPA rating of 35 miles.

Sure, both companies prefixed those numbers with "up to"--but most people see only the number, not the qualifier.

Will Tesla be proactive?

We hope Tesla gets out in front on this one. EPA ratings of 120 miles, 173 miles, and 225 miles for its "160-, 230-, and 300-mile" models wouldn't help the Model S or electric cars in general.

But perhaps EPA ratings for the three Model S versions will come close to the electric ranges that the company has been quoting.

Even if that proves to be the case, Tesla needs to communicate very clearly to its buyers that if they drive fast a lot, their range will fall.

Aerodynamic drag, starting around 40 mph, increases the amount of energy required to move a car through air resistance on an exponential--not linear--basis.

That is, the energy needed to keep a car moving at 80 mph is not double that required at 40 mph, but closer to the square of the increase.

We'll let you know if we hear anything further from Tesla.


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