Nikola Tesla was a genius who, more than 100 years ago at the dawn of the electric age, invented alternating electrical current, the radio, and the AC motor, among other things, that are instrumental to our modern life. Now, in the 21st century, Tesla Motors is trying to reinvent the automobile, and we spent a day driving the company’s first product, the Tesla roadster.
Based on the Lotus Elise, the Tesla is a high-performance sports car motivated by a completely electric powertrain—meaning, an electric motor juiced by a battery. For those who believe such a powertrain is only suitable for overgrown golf carts—the various Th!nk and GEM products, for example—the Tesla is a revelation.
On a wet public road, with mediocre traction, we measured a 0-to-60-mph time of 4.4 seconds (shifting at 62 mph) and a quarter-mile of 13.3 seconds at 104 mph (shifting at 45 mph, which is what’s represented in our spec panel). Even more impressive is the instant acceleration at real-world speeds of 30 to 100 mph. Squeeze the throttle, and the Tesla surges forward with effortless ease.
Our top-gear acceleration measured 2.3 seconds for the 30-to-50- and 50-to-70-mph intervals. The Tesla’s 4.6-second total for the two tests bests that of a Mercedes-Benz CLK63 AMG Black Series, which was our 2007 champion in this measure of instant responsiveness.
This performance is not accompanied by the usual sound of an electric car, namely, the manic whine of a 120-volt sewing machine plugged into a 220 outlet. Instead, the wind whistle and the road and tire noises you’d expect in a Lotus dominate your aural landscape. It helps that the device that makes this performance possible sits between the electric motor and the cockpit.
We’re talking about the Tesla’s giant battery pack. It fills the space where the Elise’s mid-mounted, Toyota-sourced powertrain was once located. The Tesla’s powerful battery consists of 6831 lithium-ion cells arrayed as follows: 69 cells wired in parallel make up a brick; nine bricks in series form a sheet; and 11 sheets in series make up the complete battery.
The individual cells are standard “18650” Li-ion units. They’re about a third bigger than standard AA cells that are commonly used, by the handful, to power laptop computers. The Tesla battery is distinguished by its huge size and the extensive temperature sensors and cooling passages it incorporates.
Propylene glycol, a coolant related to the standard antifreeze, ethylene glycol, flows through the battery to equalize its temperature. If the battery starts to get too warm, the glycol is cooled by the air-conditioning system to lower the battery temperature, although this isn’t required much in normal driving. Tesla engineers assured us the battery could be maintained below its maximum allowable temperature of 122 degrees even during summer in Death Valley.
The 6831 cells weigh 700 pounds. Add the wiring, the sensors, the cooling tubes, and a housing, and the complete pack tips the scales at nearly half a ton. With the 248-hp electric motor and two-speed transmission placed above the differential and behind the battery, 65 percent of the Tesla’s 2700-pound curb weight is on the rear wheels. The last Elise we tested had 61 percent of its 1930-pound weight on its rear wheels.
Despite the extreme weight bias, the Tesla handles well. During fairly hard running on Skyline Drive near Tesla’s headquarters in San Carlos, California, the roadster felt responsive, balanced, and secure overall. The day was wet and foggy, so we were not encouraged to explore the car’s limits, but we felt comfortable pushing way harder than any other driver we encountered on the road.
At low speeds, the Tesla’s unassisted steering is heavy, but once over 25 mph, the effort feels comfortable. Same goes for the ride, which can be harsh and unyielding in town over speed bumps and potholes. At highway and back-road speeds, however, the Tesla’s ride is smooth and supple.
Credit for this performance goes to several changes to the Lotus chassis for the Tesla application. The aluminum extrusions used for the structure’s main side rails are stronger to cope with the increased weight and shallower to ease entry into and exit from the cockpit. A modified rear subframe accommodates the electric powertrain and uses different lower control arms with revised geometry. Bigger brakes and five-bolt wheels have been added, along with slightly smaller front tires, to better match the cornering grip to the weight distribution.
Although we had no opportunity to measure the Tesla’s stopping distance, the brakes felt strong and perfectly smooth. That’s because the regenerative braking used to recover some of the car’s kinetic energy when slowing down operates separately from the braking system.
When you release the accelerator on the Tesla, the electric motor goes into full regen, delivering as much as 44 pound-feet of braking torque to the rear wheels. To coast, without any engine braking, you need to partly depress the throttle to the point where the dashboard gauge shows current flowing neither into nor out of the motor.
In town, the driver can take advantage of this strong accelerator-controlled regen to drive the Tesla at moderate speeds without touching the brake at all. And when you do apply the brake, it has a purely hydraulic feel, unpolluted by blended regenerative braking.
2008 Tesla Roadster Specs
VEHICLE TYPE: mid-motor, rear-wheel-drive, 2-passenger, 2-door targa
BASE PRICE: $98,000
MOTOR TYPE: AC permanent-magnet synchronous electric
Power (SAE net): 248 bhp @ 8200 rpm
Torque (SAE net): 200 lb-ft @ 0 rpm
TRANSMISSION: 2-speed manual
DIMENSIONS:
Wheelbase: 92.6 in Length: 155.4 in Width: 69.0 in Height: 44.4 in
Curb weight: 2700 lb
C/D TEST RESULTS
Zero to 30 mph: 1.7 sec
Zero to 40 mph: 2.4 sec
Zero to 50 mph: 3.6 sec
Zero to 60 mph: 5.0 sec
Zero to 70 mph: 6.2 sec
Zero to 80 mph: 7.7 sec
Zero to 90 mph: 9.8 sec
Zero to 100 mph: 11.7 sec
Zero to 110 mph: 15.2 sec
Street start, 30–50 mph: 2.3 sec
Streer start, 50–70 mph: 2.3 sec
Standing ¼-mile: 13.3 sec @ 104 mph
Top speed (drag ltd, mfr’s claim): 125 mph
Sourse: Automobile Car Blog
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