AC Propulsion tzero

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The AC Propulsion tzero with the top off

The tzero is a hand-made electric sports car that was produced in limited numbers by the U.S. company AC Propulsion. The tzero is 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.

Original Lead acid battery pack

New Lithium Ion battery pack

The original version of the roadster runs on 28 Optima Yellow Top Lead Acid batteries which produce 150 kW (200 horsepower) and 177 lbf·ft (240 N·m) of torque at 336 volts (this 28 * 12 V battery-equivalent) which rockets the 1040 kg car from 0 to 60 mph in 4.07 seconds. The single gear ratio limits the car's maximum speed to 90 mph (145 km/h) at 12,000 rpm, although it is said that early prototypes fitted with multiple gear ratios could hit 155 mph (250 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 miles (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. Within a single hour, the car can be charged from 0-95%. The base price of this version was to have been USD $80,000.

A second prototype was built in August 2003, powered by 6,800 lightweight lithium-ion cells, similar to those that make up the battery packs of laptop computers, giving it a 300 mile (480 km) range. Lighter than the original version by 700 pounds (320 kg), the 2003 edition goes from 0-60 mph in 3.6 seconds. The single gear ratio limits the car's maximum speed to just over 140 mph (225 km/h) at 13,000 rpm with proper gearing, though it has never been tested at greater than 105 mph (169 km/h). The base price of the car was USD $220,000.

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.

AC Propulsion also produced a portable internal combustion powered generator mounted on a trailer known as the Long Ranger that could be towed behind the car and feed power to the batteries during travel. The trailer used a 500 cc Kawasaki engine with a 9.5 U.S. gallon (40 liter) fuel tank and achieved 30 to 35 mpg over at least 20,000 highway miles. It is rated at 20 kW DC output and can maintain 60 to 80 mph. Video footage of the backtracking feature, which allows drivers to easily back a trailer through a set of slalom cones, can be seen here.

ACP Backtracking Genset trailer

Due to high production costs, however, AC Propulsion ceased to produce the tzero. Only three still exist, one of which is owned by the company itself and the other two privately. The drivetrain was also used in the Wrightspeed X1.