One wheel engaging before the other just sounds like your trims are out a little. Move the slider (or click button) below the stick on the aileron axle left or right in small increments until both motors/wheels turn at the same time. Bear in mind that some motors aren't neutrally timed too, so will spin faster in one direction than the other. Since motors are generally fitted back-to-back or opposite to each other, this can affect the straight line ability of your robot and can be cancelled out by sensitive adjustment on the transmitter stick when driving, but most of the time it's not severe enough to be a problem.