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As season two draws to a close this weekend, here’s a refresher of the technology that lurks under the skin of the world’s first all-electric single-seater series. At the start, all the cars were the same Dallara-Renault STR_01E, but for this season the rules were opened up allowing for technical development in numerous areas, including motors, gearboxes, rear suspension and wheels.
The cars
The chassis are the same as season one. They were built by Italian racing car specialists Dallara and are made of a carbon fibre/aluminium honeycomb composite. They have been crash-tested to the same stringent standards as Formula 1. Each of the nine teams has four cars.
The bodywork, wings and suspension are produced by a French company called SPARK, which was established especially for Formula E. For season two, the teams are allowed to produce their own rear suspension. The settings need to be the same on both sides and the wheelbase has to be the same as in season one.
The large fairings on the front wing are designed to minimise the wind resistance caused by the front wheels, while the two large fins that protrude from the side of the chassis are part of the crash structure and offer no aerodynamic benefit.
Motor
The motor takes the energy produced by the battery and uses it to drive the wheels. In season one, McLaren produced the motor. This is still being used by Andretti and Team Aguri.
The other manufacturers have produced their own version. Most have opted for a single motor, but DS Virgin Racing and NEXTEV have gone for two. Torque vectoring – using a motor on each wheel to effectively create traction control – is outlawed and a common differential is used on all cars.
Invertor
This component takes the electricity that is created by the battery and converts the charge from a direct current (DC) into an alternating current (AC), which is used by the motor to drive the wheels. For this season the teams were free to use their own design, with the main benefits to be found in terms of size, weight and packaging.
Gearbox
The gearbox is used by the driver to make the most efficient use of the power delivered from the battery via the motor. In season one a five-speed Hewland gearbox was used by all the teams. Andretti and Team Aguri will still employ this. Dragon, Mahindra and Venturi use a modified version of this that has four speeds, while Abt has gone down the three-speed route. Renault produced a very small, light, two-speed gearbox cased in carbonfibre, while the twin motor runners use a single-speed transmission.
All the teams have to use the same powertrain component all season, but they can employ one joker changes for each element of the powertrain.
Battery
All the cars use the same battery. It is built by Williams Advanced Engineering and produces 28kw/h of energy. In qualifying mode it runs to a maximum power of 200kw (roughly 270bhp). In race mode the cars run at a maximum of 170kw (roughly 225bhp). This is an increase of 20kw over season one and means the cars and drivers that use and harvest their energy most efficiently are able to go the fastest for longest.
Tyres
Michelin created bespoke racing tyres for Formula E. They are distinctive in two ways. Firstly, they are low-profile and designed for 18-inch rims, which means they look very different to the high-profile, 13-inch tyres used in Formula 1. Secondly, the tyres are treaded, which means they can be used in both wet and dry conditions.
The reason for both of these is increased efficiency in terms of rolling resistance (profile) and the number of tyres needed (tread). A traditional racing slick cannot be used in wet conditions, which means wet (and sometimes intermediate) tyres need to be transported to races just in case it rains. Often they are never used, which is an unnecessary waste of CO2.
To see these amazing machines in action for the last time in Battersea Park, get your tickets for the Visa London ePrix on July 2 and 3 here.