.....from the chief engineer at one of the FE race teams.... (An old quote but still applicable..)
Also......“Simply put, using a gearbox helps you to extract the maximum efficiency possible from your chosen electric motor and to stay at full power for as long as possible at all road speeds,” says Vin Patel, chief engineer at Mahindra Racing. The Indian team has elected to use a four-speed ’box in season two, dropping a gear from the first season unit. “Motor efficiency varies greatly depending on its architecture and design philosophy. This mainly translates as variations of efficiency at different motor speeds.”
In the second season, different motors are in use, with a twin-unit configuration found at DS Virgin Racing and NextEV TCR and single motors from varying suppliers employed elsewhere in the pit lane. Mahindra Racing’s M2Electro uses a revised and updated version of the McLaren unit used in season one, developed in partnership with McLaren Applied Technologies. Altering the specification of key components of the motor, improving materials used and revising software controls resulted in a 20% increase in peak torque and a 15% increase in rpm.
“Some motors might rev up to 25,000rpm while others only reach 9,000rpm,” Patel goes on. “They will be delivering very different torque bands, which need to be translated into extracting maximum permitted power from the battery. Using a gearbox helps you keep the motor in the most efficient operating range possible.”.......
Renault, The winning team last year, used a 2 speed only transmission with the lower gear devoted solely to "launch" the car from the start (IE, Torque increase at the wheels)