Why transmission matters when matching a driver
Not every driver is equally comfortable with every car. Telling the team that your car is a manual gearbox lets them look for a driver who has experience with it, rather than finding out on the day.
Share the car model and any particular behaviour you would like the driver to know about, such as a heavy clutch or a tall vehicle. This helps the team review suitability before assignment.
If you own both an automatic and a manual car, mention which one will be used. The automatic car driver page covers the other case.