The tzero is a handmade electric sports car designed and built in very limited numbers by the U.S. company AC Propulsion. The tzero was based on the Piontek Sportech kit car, which consists of a fiberglass body built over a reinforced steel space frame with double wishbone independent suspension and rack and pinion steering. AC Propulsion added the AC-150 drivetrain, a single-speed electric system with an overall gear ratio of 9:1. Launched in January 1997, only three prototypes were built and plans for commercial production were dropped in mid-2003. The name comes from t0, the mathematical symbol for a starting point in time. Due to high production costs, AC Propulsion ceased to produce the tzero. As of 2009, only three still exist; one of which is owned by the company itself, one by Gruber Power Services, a company that specializes in Tesla Roadster repair, and one privately. The drivetrain, however, was used in many other vehicles. Because the car recharges its batteries when the throttle is released — slowing sharply as energy is recaptured — it can be driven hard using only the accelerator pedal. Also, if the car detects a turn with more than half a g-force (5 m/s²), it eases the rear-wheel regenerative braking to prevent slides.
Original lead-acid battery powered tzero
The original version of the roadster ran on 28 Johnson Controls Optima Yellow Top lead-acid batteries in series, which produced 150 kW (200 horsepower) and 177 lbs·ft (240 N·m) of torque at 336 volts and accelerated the 1,040 kg (2,290 lb) car from a standstill to 60 mph (97 km/h) in 4.07 seconds. The single gear ratio limited the car's maximum speed to 90 mph (140 km/h) at 12,000 rpm, although it is said that early prototypes fitted with multiple gear ratios could hit 155 miles per hour (249 km/h). Even with the single ratio, lead-acid models are capable of completing a quarter mile (400 m) drag race in 13.24 seconds. The expected range per charge of the tzero with the lead-acid batteries is 80 to 100 mi (130 to 160 km) as a result of consuming only 180 watt hours per mile (895 J/km) (DC) on the highway and due to regenerative braking. The car can be charged from 0 to 95% within an hour. The base price of this version was to have been US$80,000.
Lithium-ion battery conversion
Martin Eberhard commissioned a conversion of the original tzero battery pack from lead-lead acid to 6,800 lightweight lithium-ion cells similar to those that make up the battery packs of laptop computers. The conversion was done over six months from March through September, 2003 and gave the tzero a 300-mile (480 km) range. Lighter than the original version by 500 lb (230 kg), the lithium-ion conversion goes from 0–60 mph (0–97 km/h) in 3.6 seconds. The single gear ratio limits the car's maximum speed to just over 140 mph (230 km/h) at 13,000 rpm with proper gearing, though it has never been tested at greater than the electronic limit of 105 mph (169 km/h). The base price of the car was US$220,000. Martin Eberhard encouraged Tom Gage and Alan Cocconi to move the lithium-ion powered prototype into production. When they declined, Martin Eberhard and Marc Tarpenning incorporated Tesla Motors in July, 2003 to pursue commercializing the tzero. Eberhard then borrowed the converted tzero for three months as part of his pitch to persuade venture capitalists to invest in Tesla Motors.
JB Straubel then told Elon Musk about the newly converted, now lithium-ion powered tzero and arranged a test drive. Musk also encouraged AC Propulsion to commercialize the vehicle. Tom Gage, however, again deferred in favor of working on their electrified Scion xB called the eBox; but, he put Elon Musk in contact with Martin Eberhard which led to Elon Musk's Series A funding of Tesla Motors in April, 2004 and their hiring JB Straubel.
Long Ranger genset trailer
AC Propulsion also built a portable internal combustion powered generator mounted on a trailer known as the Long Ranger that can be towed behind the car and feed power to the batteries during travel. The trailer uses a 500 cc Kawasaki engine with a 9.5 U.S. gallon (40 liter) fuel tank and achieved 30–35 mpg‑US (7.8–6.7 L/100 km; 36–42 mpg‑imp) in highway driving over at least 20,000 mi (32,000 km). It is rated at 20 kW (27 hp) DC output and can maintain 60–80 mph (97–129 km/h). The trailer incorporates a novel "backtracking" feature that automatically steers the trailer wheels allowing even novice drivers to easily back a trailer through complex maneuvers; the company published a video demonstrating the ease with which the trailer could be backed through a set of slalom cones.