The cold rain that had been falling on Northern California in mid-January paused before we silently rolled the roadster out the development garage in San Carlos.
With the sun shining for a least a short time, the top was easily removed by releasing a pair of latches on each side and rolling it up. The top and two support ribs are easily be stored in the relatively spacious trunk area at the back of an otherwise petite car.
But this is no typical high-performance roadster, this is the Tesla Roadster.
Eighteen months after giving the world a glimpse of the Tesla Roadster in a Southern California aircraft hanger, Tesla Motors is just about ready to launch limited production of their all-electric sports car and is allowing selected members of the media behind the wheel for the first time.
Green Fuels Forecast paid a visit to Tesla's headquarters in San Carlos, CA to spend some time talking to the engineers and learning more about the car before setting out for a drive.
When Martin Eberhard and Marc Tarpenning launched Tesla Motors five years ago, the goal was to create a high performance electric sports car with zero emissions. Eberhard likes driving but wanted to be environmentally friendly. He drew inspiration from the “tzero” created by AC Propulsion, but the company declined to produce or sell any copies of the car. This prompted Eberhard to start gathering together a team to develop a similar car for himself and anyone else who wanted to buy one.
With the intention of building a self-sustaining electric vehicle business that wasn’t dependant on sales of clean air credits of questionable value, Tesla decided to start at the top end of the market. The company is building a relatively low volume, high-priced car to generate enough revenue to cover the development of the technology before it is spread to higher volume applications.
The Tesla team set about developing a lithium ion battery pack and a powertrain to harness it. Lithium ion batteries have much higher energy and power density than previous chemistries such as nickel-metal-hydride and lead acid. Lithium batteries are now commonly used in most consumer electronics (CE) devices. There are many varieties of lithium batteries that use lithium for the cathode material and an assortment of different materials for the anode. The most common type used for CE applications use a metal oxide such as cobalt oxide for the anode material.
While this type of chemistry has the best energy density, it is also subject to thermal runaway if the temperature is not managed carefully. Due to their small size, CE devices typically have no battery cooling mechanism and they use the full capacity of the battery. This leads to batteries running hotter than they should, in turn causing the electrodes to crack, reducing the capacity of the battery to hold a charge.
When Tesla's engineers began development, no company had created a large format lithium ion battery optimized for automotive applications. With a target of producing a high performance car with a useful range of 250 miles per charge, the only viable option was lithium-metal-oxide batteries. The Tesla team chose to use off the shelf lithium cells of the type used in laptop computer battery packs.
In order to reach the performance targets, a 53kWh pack was designed. Because of the need to meet all regulatory requirements for vehicle safety, the integrity and robustness of the pack was critical. Using existing CE cells to reach 53kWh required 6,831 cells. These are assembled into pack consisting of 11 individual modules, each of which has liquid cooling circuits running throughout.
The cooling circuit contacts every individual cell in the pack. Temperatures throughout the pack are monitored to ensure they remain uniform across the pack and the overall temperature remains within the optimum range for durability and performance. The pack is also constructed to ensure integrity in the event of an accident. The day before the drive, Malcolm Powell, Tesla's vice president of vehicle integration, announced the Roadster had met all regulatory requirements and had been approved for sale in all 50 states.
Once the top and camera gear were stowed away in the relatively spacious trunk, we headed west through the streets of San Carlos and up into mountain range the separates the San Francisco Bay coastal area from the Pacific coast. When approaching the Tesla Roadster, the first impression is how small it is. Tesla put its initial focus on developing an electric powertrain and teamed up with Lotus Engineering for the chassis engineering and final assembly. The Lotus Elise was chosen as a donor car to form the basis of the Roadster.
The extruded and bonded aluminum chassis of the Elise was heavily modified with a longer cockpit for more interior room and a completely different rear structure to support the battery pack and electric motor. The Elise is one of the smallest and lightest sports cars on the market and this largely contributes to making the Roadster possible. Even with a nearly 1,000lb battery pack wedged into the center of the car directly behind the seats, the Roadster still comes in at a relatively modest 2,690lbs, almost 700lbs more than the Lotus.
Even though the chassis has been stretched to better accommodate taller drivers, it is by no means roomy. The side sills are wide and the car sits very low. The seats are single piece shells upholstered in either leather or a suede-like micro-fiber. Adjustments are limited to fore-aft position. The arthritic or horizontally challenged need not consider the Tesla Roadster. If on the other hand the car fits a prospective owner's physique, it may well be the perfect tool for a blast down a twisty back road.
Those familiar with the Lotus will recognize the lineage in overall shape, the windshield and mirrors. Under the skin, the Elise suspension design is largely carried over. This is a good thing since the Elise is considered one of the best handling sports cars in the world. Overall, Tesla estimates that about 15 percent of the Elise parts are carried forward into the Roadster, with rest of the car consisting of modified versions or unique components.
Another component unique to the Roadster is the AC induction motor. The 248hp motor is about the size of a watermelon and produces over 200lb-ft of torque from 0rpm up to over 6,000rpm before tapering off down its 13,000rpm maximum. Originally unlike most electric cars, the Roadster was designed to use a two-speed transmission to provide acceleration to 60mph in 4 seconds while maintaining a 125mph top speed and a reasonable range.
Production of the Roadster has been delayed by about nine months due to issues with durability of the transmission. Since the motor torque is not reduced during shifting, three different transmission suppliers were unable to produce an adequate unit. As a result, the company has now decided to go with an in-house, single-speed transmission. The power electronics module (PEM) is being upgraded to support higher current levels to the motor. The motor also is being modified with a liquid cooling system that had been developed for Tesla's next project, the WhiteStar sedan. This will allow the motor to produce more power under hard acceleration. The Roadster will now be able to reach the acceleration target and the maximum speed without ever shifting gears.
The car available for tests still has the air-cooled motor and a two speed with the lower gear locked out. The early production cars will be similarly equipped although the transmissions will actually be built without the lower-gear. Once the new powertrain that Tesla calls DriveTrain 1.5 is validated later this year, the early production cars will be retrofitted at no cost to owners.
Even with the interim drivetrain, the Roadster is a seriously fast car. The instant torque response of the electric motor means the pressing the accelerator pedal immediately translates to higher velocities. Climbing up into the mountains, where most cars, even those with much more power would require a downshift or two to accelerate, the Roadster just pulls and pulls. The experience is unlike anything except perhaps a powerful diesel engine vehicle thanks to the seamless and instant nature of the motor.
The instantaneous response is also perfect for shooting from one corner to the next along Skyline Blvd. When the time comes to change direction the Roadster chassis is capable of maintaining a remarkable amount of momentum while cornering. Even on the cold, damp and sometimes bumpy pavement during the drive, the suspension keeps the tires firmly in contact allowing them to do their job. Like it's ancestor, the Roadster has unboosted steering, and double wishbone suspension at all four corners.
The suspension transmits complete information about the road surface to the driver with just enough filtering to cut off the peaks and prevent it feeling harsh. It's not luxury car compliant, but it doesn't beat up the occupants either.
The steering is otherworldly. The vast majority of American drivers today have likely never experienced a car with unboosted steering unless they happened to be trying to maneuver a car with the engine off. The Roadster has a tiny MOMO steering wheel with a thick rim, the perfect tool to transmit directional inputs to the front wheels. Like the suspension, the steering geometry seems ideally calibrated to these conditions. The torque feedback through the steering wheel feels perfectly in proportion to the lateral grip being generated.
Road imperfections can be felt, but only to the extent that they are informative. At low speeds, such as maneuvering around a parking lot, the steering effort can be a bit on the heavy side but as speeds climb above about 20mph, all doubts fade away.
The Tesla Roadster is certainly not a car for everyone. Many people simply won't fit comfortably in the car. Most people can't afford the $100,000 price tag. Its utility for long trips is limited by the need to stop every couple of hundred miles and plug in for several hours, not to mention its size. There is also the thorny issue of long-term durability of the battery pack and potential replacement cost.
But for those who have the means and dimensions and desire an emissions free way to traverse a twisty road at high speed, this high tech machine can't be beat. Eberhard is no longer directly involved with Tesla Motors, but the vision he had for a zero emissions sports car seems to have come to fruition.