Tesla Roadster — In Depth

In 2005, rumors started to spread in the automotive world about an electric sports car powered by thousands of laptop batteries. The whole idea sounded preposterous. Who would build such a car? The batteries would weigh so much, the car would probably have only modest acceleration and handle more like a truck than a nimble two-seater with sporting pretensions.

Meet the Tesla Roadster

The Tesla Roadster is a Lotus Elise chassis married to a lithium-ion battery pack and an electric motor driving the rear wheels through a one-speed transaxle. Tesla contracted with Lotus to provide a total of 2,500 cars manufactured without a drivetrain. Ultimately, a total of 2,450 Roadsters were sold between 2008 and 2012.

The battery pack — which Tesla calls the Energy Storage System — is comprised of 6,831 lithium-ion cells arranged into 11 sheets connected in series. Each sheet is made up of 9 bricks connected in series, and each “brick” contains 69 lithium-ion cells (“18650” lithium-ion cells) connected in parallel. An 18650 battery cell is cylindrical in shape, approximately 18 millimeters in diameter, and 65 millimeters in length.

The 18650 cells were selected because they were readily available and reasonably affordable.

The Tesla Roadster was shown to the public for the first time on July 19, 2006, in Santa Monica, California. It was an invitation event for 350 people held at the Barker Hangar at the Santa Monica airport. The car was also featured at the San Francisco auto show on November 18 that same year. It went on to be part of international auto shows in Los Angeles, Detroit, and Frankfurt, Germany.

Production Begins in 2008

Tesla CEO Elon Musk took delivery of the first production car in February 2008. That car had an AC induction motor rated at 248 horsepower, 200 lb-ft of torque, and a two speed transmission. Later in 2008, the Roadster 1.5 was offered with a single speed gearbox. In 2009, the Roadster 2.0 offered a motor with 288 horsepower and 273 lb-ft of torque. A Sport version had the same horsepower but 295 lb-ft of torque. A Special Edition Roadster 2.5 was offered in 2011. Its specifications were the same but it featured special paint and trim as production drew to a close.

The Sport was the fastest Roadster of all. It galloped to 60 mph in 3.7 seconds, 0.2 tenths faster than its siblings. According to the EPA, the Roadster had a range of 244 miles and was rated at 120 MPGe, meaning its efficiency was equivalent to a gasoline-powered car that got 120 miles per gallon.

Tesla’s contract with Lotus ended in December 2011. Production ended less than a month later due to a lack of chassis available for Tesla to convert. Sales in the US ended in August 2011, when regulations regarding two-stage air bags went into effect. The Lotus Elise was not engineered with the advanced airbags in mind and making the necessary modifications was deemed to be too expensive.

Origins of the Tesla Roadster

The car that came to be known as the Tesla Roadster actually traces its heritage back to 1994 and a company called AC Propulsion located in San Dimas, California, approximately 30 miles east of Los Angeles. It developed the AC-150, a 200 horsepower integrated drive system for compact to mid-size passenger cars. The key to the AC-150 powertrain was the use of an AC electric motor. It was the kind of device envisioned by Nikola Tesla before his death in 1943.

Motors that run on alternating current are lighter and less expensive to build than the direct current motors favored by manufacturers of subway cars and locomotives. They require an inverter, however. That is a device that converts the DC power stored in batteries to the AC current needed to operate the motor. Inverter technology in 1994 was rudimentary compared to what it is today.

In 1997, AC Propulsion fitted a Piontek Sportech kit car with its AC-150 system. The Sportech consisted of a fiberglass body mounted on a reinforced steel space frame with double wishbone independent suspension and rack and pinion steering. It called the car the tzero. In scientific circles, the lower case “t” is often used as a shorthand notation for time. “Zero” connotes a beginning. In other words, the tzero was intended to be the first real electric car and the first car in the electric car revolution. To say that AC Propulsion was ahead of its time is a gross understatement.

From Lead-Acid to Lithium-Ion Batteries

The original tzero used 26 lead-acid batteries. Although AC Propulsion intended to put the car into production, only three were ever built. The car was simply too expensive for mass production. In early 2003, Martin Eberhard approached AC Propulsion and requested they replace the lead-acid batteries with a battery pack made up of 6,800 lithium-ion laptop batteries.

Is it a coincidence that the Tesla Roadster used a battery pack with 6,832 lithium-ion batteries? No, it is not. Eberhard went on to become a co-founder of Tesla Motors in 2003, along with Marc Tarpenning. The conversion was carried out in the spring of 2003. When it was competed, the car weighed 500 lbs less and its top speed increased from 90 mph to 140 mph. Eberhard then borrowed the car to show it to potential investors in Tesla Motors.

Enter Elon Musk & JB Straubel

One of the people Eberhard showed the car to was JB Straubel. He in turn showed it to Elon Musk. Musk, who made his first fortune as the father of PayPal, decided to invest $7.4 million into Tesla Motors. He became heavily involved in the company and used the tzero to promote his dream of building premium electric cars.

Eberhard and Tarpenning envisioned starting with less expensive cars that mainstream buyers could afford but Musk was adamant that the best strategy was to start by building premium luxury cars that would appeal to wealthy opinion makers. Eventually, the two split with Musk over what direction the company should take. They cashed out their Tesla stock and went off to pursue other ventures. Musk took over as CEO and Straubel became CTO, positions they hold to this day.

Comparing the Tesla Roadster to the Lotus Elise

Although the Tesla Roadster is based on the Lotus Elise, only about 6% of the parts are interchangeable between the two cars. The Roadster is built on a chassis that has been lengthened by 2″. Only the windshield, airbags, some tires, some dashboard parts, and suspension components are common to both. The Roadster’s single-speed gearbox was made in Detroit to Tesla’s specifications by BorgWarner in Auburn Hills, Michigan. Brakes were made by Siemens in Germany.

Roadsters for the North America market were sent to Menlo Park, California, for final assembly. Cars for customers elsewhere were completed at a facility in Wymondham near the Lotus factory in Hethel.

The Top Gear Controversy

In late summer of 2008, the BBC show Top Gear tested two production versions of the Tesla Roadster at its test facility. The Roadster proved to be faster in a straight line than the standard Lotus Elise. At one point, Jeremy Clarkson, Top Gear’s most notorious bad boy can be heard exclaiming, “God Almighty! Wave goodbye to the world of dial-up, and say hello to the world of broadband motoring!” He then remarked, “This car is biblically quick!”

Sadly, the testers found the car to be lacking a bit in cornering prowess — not unexpected since it was weighted down with 1,000 lbs of batteries carried high in the chassis. Top Gear reported the car only went 55 miles on a battery charge during its admittedly rigorous use. At one point, a Roadster was filmed being pushed off the track, suggesting it had run out of power.

Elon Musk was furious and Tesla actually sued the BBC for libel but ultimately lost the case in the British courts. In the end, the controversy brought Tesla a world of free publicity. Public awareness of the Tesla Roadster specifically and electric cars in general can be traced directly to that episode of Top Gear and the controversy that followed. As politicians are fond of saying, “Write whatever you want about me. Just make sure you spell my name right.”

A Battery Upgrade & A New Roadster

Tesla says it has partnered with LG Chem to develop an upgraded battery for the original Roadster. Lithium-ion battery technology has come a long way in the past decade or more. The new battery pack, which costs $29,000 and has 40% more capacity, is rated at 80 kWh versus the original 52 kWh. The extra capacity gives the Roadster enough range to go from Los Angeles to San Francisco on a single charge.

The company says the cost is high because the new battery packs are built by hand at the rate of only one or two a week. Removing the old battery and installing the new one is a labor-intensive process that includes a new power controller and associated electronics. Roadster owners can also elect a separate upgrade that adds new, more aerodynamically efficient bodywork and low-rolling-resistance tires to further boost range.

Tesla says it intends to offer an entirely new Roadster based on a shortened version of the Model S chassis for model year 2019. No other details are known at this time.

What is the Tesla Roadster Like to Drive?

The Tesla Roadster was priced at $98,000 in 2008. That number had risen to $109,000 a year later. Did owners get value for their money? In November of 2009, Jason Cammisa, west coast editor for Automobile Magazine, spent a week driving one. He reported the car “explodes off the line, pulling like a small jet plane. It’s like driving a Lamborghini with a big V-12 revved over 6000 rpm at all times, waiting to pounce — without the noise, vibration, or misdemeanor arrest for disturbing the peace.”

Later he took the car to Infineon Raceway in Sonoma, California, to put it through its paces on track. He praised the car for its robustness, saying it “wins the Coolest Car I’ve Ever Driven award. Why? Despite the flat-out sprints, the drag racing, the donuts, the top speed runs, and dicing through traffic like there’s a jet pack strapped to the trunk, Pacific Gas and Electric — which generated power for the Tesla — released into the atmosphere the same amount of carbon dioxide as would a gasoline powered car getting 99 mpg.”

He added, “And the Roadster didn’t break. It didn’t smoke, lock up, freeze, or experience flux-capacitor failure. Over the past ten decades, no company has been able to reinvent the car — not General Motors with the EV1, not Toyota with the Prius. And now, a bunch of dudes from Silicon Valley have created an electric car that really works — as both an environmental fix and a speed fix.”

You aren’t likely to find any higher praise for a car than that.