[autoavia]

My understanding is that an inline car will always move sideways slightly under braking because the crown gear is off centre in the chassis but the movement is magnified when the brakes are turned up so far that the rear wheels lock. Turning the brakes down a little stops the rear wheel lock and reduces the sideways movement.
 The problem can also be magnified by poor car set up such as a rear axle which isn't parallel to the track.

 Incidentally full size go karts have exactly the same problem. The offset drive to the motor doesn't seem to have too much effect but the offset disc brake on the rear axle produces a very noticeable turning moment when you brake hard which affects the steering.