How to transform PC controls to Touchscreen controls

So here is the moving forward script for PC:

wheelRR.motorTorque = maxTorque * Input.GetAxis("Vertical");
wheelRL.motorTorque = maxTorque * Input.GetAxis("Vertical");

And the touchscreen (Android) button:

...
if (touch.phase == TouchPhase.Stationary && gasButton.HitTest (touch.position)) {
    			//how should i type the moving forward script here to work? 
    	}

why do i need this? because i have a lot of scripts for carcontrol, but they work on PC, how to make them for Android?
example: http://s3.postimg.org/wd35m2bwz/screenshot_1306.png

how to make all this for Android?

as you can see from the documentation Input.GetAxis is passing float between -1 to 1.
so calculate this value from your touch location and pass it to the wheelRR.motorTorque with variable.