I have a job interview tomorrow at a company called Drive System Design who have a fairly strong focus on EV and HEV power trains. One of their products (well, developed by a sister company) is an EV transmission system claiming to achieve 'up to a 15% reduction in energy consumption on the New European Driving Cycle (NEDC) compared to a single speed EV powertrain and offers a 40% weight saving to the power train.' I was always under the impression that EVs didn't NEED multiple gears because their AC induction motors have an almost flat torque/speed characteristic and reach max efficiency at around 20% load and then stay there. Tesla's choice of a single-speed transmission seems to support that. Plus any additional gearing and mechanical components increase losses to friction. So what's the situation here? How can a multi-speed transmission increase efficiency, and more suprisngly, save weight? If this is the case, what is Tesla's reason for sticking with single-speed transmission? I'm interested in talking about this at my interview tomorrow but it would be good to have some context or understanding of this before I go.