Help In Making a SphereCast for 3D Tire! Working RayCast Script included!

Hello,

I am wondering if using a Sphere Raycast is a good idea for a vehicle tire? I want to develop a rock Crawler game :D iOS.

DOCS: http://docs.unity3d.com/Documentation/ScriptReference/Physics.SphereCast.html

Is high speeds a problem? What are the concerns and is it hard to do?

HERE is my FULLY working Raycast Tire system, I would LOVE it if someone could help me transpose it to using SphereCast :D.

CODE:

 var wheels:iWheels[];
 private var skid:Skidmarks;
 private var slip:float=1.0;
 private class iWheels {//Wheel set
     var collider : WheelCollider; 
     var wheelPref : Transform;
     var driveWheel : boolean = false;
     var steerWheel : boolean = false;
     var rearWheel : boolean = false;
     var lastSkidmark : int = -1.0;
     var rotationValue : float = 0.0;
 }
 
 
 
 
 
 function Update () {
         for(var i:int=0; i<wheels.length; i++){//for each wheel
               var hit : RaycastHit;//We will define WHAT the raycast hit here.
              var whPref = wheels[i].wheelPref; //For each of the wheels, we will create a prefference based on if this is a (Steerable wheel, drive wheel, front wheel)
               var ColliderCenterPoint : Vector3 = wheels[i].collider.transform.TransformPoint(wheels[i].collider.center ); // Lets find the wheel colliders CENTER point in a VECTOR 3, and Give that the name "ColliderCenterPoint".
           
           if (Physics.Raycast( ColliderCenterPoint, -wheels[i].collider.transform.up, hit, wheels[i].collider.suspensionDistance + wheels[i].collider.radius ) ) {// Then lets Cast a ray DOWN to the ground. Raycast( Center of wheel collider, Direction in which we cast the ray! Notice (-) symbol! That means casting DOWN, what ever it hits becomes the "hit" variable, the raycast Distance is ONLY as long as the suspension distance of the wheel collider PLUS the wheels Radius!) Thats it :D!
               whPref.position = hit.point + (wheels[i].collider.transform.up * wheels[i].collider.radius); // NOW lets Make the wheel transform (the graphic wheels) rest at the hit point, BUT we **dont** half the tire in the ground, so we mulitply the radius of the tire, to get it to perfectly (touch) the ground.
           }else{
                whPref.position = ColliderCenterPoint - (wheels[i].collider.transform.up * wheels[i].collider.suspensionDistance);//If the Raycast does NOT hit the ground put it at the FURTHEST point on the suspension distance (the HANGING tire effect).
           }
                   whPref.rotation = wheels[i].collider.transform.rotation * Quaternion.Euler( wheels[i].rotationValue, wheels[i].collider.steerAngle, 0 );//Lets make that (graphic Wheel) the same rotation value and speed as that of the wheel collider!! (NEED to see the tire spinning!!).
                   wheels[i].rotationValue += wheels[i].collider.rpm * ( 360/60 ) * Time.deltaTime;// More calculation to get the spin just right on the (Graphic Tire).
           
                   var CorrespondingGroundHit : WheelHit; //IF the wheel is HITTING THE GROUND,
                   wheels[i].collider.GetGroundHit(CorrespondingGroundHit); // Oh forgot, this makes sure we are looking at the wheel collider on the WHEEL collider, NOT the graphic tire.
           
           if (Mathf.Abs(CorrespondingGroundHit.sidewaysSlip)>8.0*Time.timeScale&&skid&&wheels[i].collider.isGrounded||Mathf.Abs(CorrespondingGroundHit.forwardSlip)>0.3*Time.timeScale&&skid&&wheels[i].collider.isGrounded) { //Basically lets see if the tire slipped :P.
                wheels[i].lastSkidmark=skid.AddSkidMark (hit.point,hit.normal,1.0,wheels[i].lastSkidmark);// If soo! then lets make that SKIDMARKS prefab do its thing! (seperate script)...
                slip=Mathf.Abs(CorrespondingGroundHit.sidewaysSlip)/70; //Lets determine HOW much the tire slipped! 
           }else{
                wheels[i].lastSkidmark=-1; //Else if it didnt slip then just make the,
                slip=0.0; // Slip equal 0 :D
         }
     }
 }

Thanks

Daniel