BLDC Motor Forward and Backward Speed

[JordanNUS86]

Hi, I'm developing a self balancing robot. To make it easy, I bought an RC car and use the chassis and its BLDC motor and motor driver. I use Basic Stamp 2 as my controller and an accelerometer from Parallax. I notice that the forward and backward speed of the BLDC motor is different. The forward movement seems to be more "wild" with higher acceleration and deceleration than the backward movement. why is that so? Is it the nature of BLDC motor? Thanks.