Car steering issue

Hi people, I've made a car in Unity 5 and facing a problem where the car steers to left or right even if I am just moving forward or reverse.. I've seen posts where people have suggested to change stiffness to a very high value but that is also not working.. Is there any other fix to it? cause its really bothering me. I am running the car on a flat surface..

If there is no fix to this, is it possible to make a suspension like system using joints and colliders ? thanks

 

I had this problem before. I found out that my box collider is not centered. Please check your box collider if it's centered or not