# How is rolling resistance accounted for in the Pacejka Curves?

I am simulating the acceleration of a car (FSAE) in a straight line. I have data of the Pacejka Curves ($F_x$ vs. $SR$) of the tire we will be using. The thing is that the curve doesn´t pass through the origin ($F_x=SR=0$). Instead the curve is shifted horizontally meaning that $F_x(SR=0)\neq0$. I have troubles finding the explanation. I am pretty sure it has to do with the rolling resistance of the tire.

My model (simplified) is as follows:

The driving torque on the axle is resisted by $F_x(SR)$ which causes a countertorque. Resultant torque is what accelerates (rotationally) the axle. $F_x$ is what drives the car forward.

Can anybody explain me the meaning of a shifted Pacejka Curve?