Vehicle control with gamepad

[pj_martins]

I was wondering if anyone could help me, I have a logitech rumblepad with two analog sticks, when on foot I can use the left analog stick to move, which is nice cause I can control the speed at which I walk. When I am in vehicle mode however, I can steer with the left analog stick and I can accelerate and decelerate with one of the gamepad buttons, but I haven't been able to figure out if there's a way you can control the vehicle's speed with one of the analog sticks as it will give me a bit of control over the speed. Does anyone know how to map the acceleration/deceleration to an analog stick?