2010 Tesla Model S and Roadster

2010 Tesla Model S and Roadster

Here's a quick rundown of the technical specs for the 2012 Tesla Model S electric four-door sedan launched today:

- BATTERY CELLS: Advanced lithium-ion chemistry yields 20-percent improvement in energy density, 50 percent more energy output over Roadster.

- BATTERY PACK: 8,000 commodity cells; standard 42-kWh pack gives 160-mile range; 230-mile (50-plus kWh) and 300-mile (70 kWh) packs to come later for rental or purchase; quicker to change than a gas tank. The 300-mile pack will use an entirely different cell chemistry than the other two.

- CHARGING: 3.5-hour charge (at 220 Volts, 70 Amps) standard, 45-minute fast charge (at 440 Volts, unspecified Amperage) available.

- DRIVETRAIN: 9-inch liquid-cooled motor between the rear wheels, output not specified; single-speed transmission; rear-wheel drive, with all-wheel-drive "in the works".

- WEIGHT:  Curb weight just over 4000 pounds; distribution 55-45, biased toward the rear.

- PERFORMANCE: 0-to-60 in 5.6 seconds; top speed 130 mph in upcoming "Sport" model.

- BODY: "Mostly" aluminum chassis and body;target coefficient of drag: 0.26 - 0.27.

- PRICE: Base price $57,400, before $7,500 Federal tax credit; base version comes with 160-mile battery pack.

- VOLUME: Tesla plans to sell 15,000 to 20,000 Model S sedans a year; the first cars will arrive in the second half of 2011, with full production a year later.

Doing the math, the performance numbers roughly pencil out. The Roadster pack has 6,381 cells, so the Model S pack has 25% more. If the newer cells have 20% greater energy density, the Model S pack would weigh about the same (990 pounds) as the Roadster pack.

But it's the power output that's key here. If the curb weight is a bit over 4,000 pounds, the pack has to move 60% more mass than the Roadster. So power output that's 50% higher will mean slightly less jaw-dropping acceleration. And indeed, the sedan's 5.6 seconds to 60 mph is higher than the Roadster's 3.9.

But keeping weight to 4,000 pounds--if 1,000 pounds of it is battery--will require an aluminum structure. Which means Tesla will likely have to create the Model S from scratch, rather than adapting another vehicle, as they did for the Roadster (which uses quite a lot of the Lotus Elise platform).

And that leads to a specification question of a totally different sort: What would it cost for Tesla to do an entirely new volume car from scratch?