Very cool idea, I think it has to do with shifting the gears but I was unable to get it to work! It seems like your fix to set it to use controller 0 did not work. Make sure your functions to get gamepad stick input are also looking for index 0. It would also be really nice to allow keyboard control. Maybe the dpad could work like the analog stick. This way people can play even if they don't have a gamepad.
In the latest version of LittleJS we added a new variable gamepadPrimary. The way it works is the first gamepad to press a button becomes gamepadPrimary. It only changes if that controller becomes disconnected. This is to fix the issue of sometimes a gamepad being on index 1 even if it is the only gamepad connected.
I am looking forward to giving your game another shot when you get it fixed!