i am trying to work with wheel collides and i am having some problems

my real problem with is is unity or my bad knowledge with coding is not liking this part "public WheelCollider[] wheelsRight = new WheelCollider[4];" "public WheelCollider[] wheelsLeft = new WheelCollider[4];"

Here is a few errors i am getting UnityEngine.Wheelcollider[]' does not contain a definition for 'radius' and no method 'radius of type 'unityengine.WheelCollider[]' could be found. are you missing assembly reference?

the error is the same for the following Radius,rpm,brakeTorque,motorTortue. and this is all unity is telling me is wrong and my pretty beginner level of coding needs a small hand to fix this problem if anyone has an answer

using UnityEngine; using UnityEngine.UI; using System.Collections;

 public class TankDrive : MonoBehaviour {
 
     public float idealRPM = 500f;
     public float maxRPM = 1000f;
 
     public WheelCollider[] wheelsRight =  new WheelCollider[4];
     public WheelCollider[] wheelsLeft =  new WheelCollider[4];
 
     public float turnRadius = 6f;
     public float torque = 25f;
     public float brakeTorque = 100f;
 
     public float AntiRoll = 20000.0f;
 
     public enum DriveMode { Front, Rear, All };
     public DriveMode driveMode = DriveMode.Rear;
     
     // Use this for initialization
     void Start () {            
 
     }
 
     public float Speed() {
         return wheelsLeft.radius * Mathf.PI * wheelsLeft.rpm * 60f / 1000f;
         return wheelsRight.radius * Mathf.PI * wheelsRight.rpm * 60f / 1000f;
     }
 
     public float Rpm() {
         return wheelsLeft.rpm;
         return wheelsRight.rpm;
     }
 
     void FixedUpdate () {
 
         float scaledTorque = Input.GetAxis ("Vertical") * torque;
 
         if(wheelsLeft.rpm < idealRPM)
             scaledTorque = Mathf.Lerp(scaledTorque/10f, scaledTorque, wheelsLeft.rpm / idealRPM );
         else 
             scaledTorque = Mathf.Lerp(scaledTorque, 0,  (wheelsLeft.rpm-idealRPM) / (maxRPM-idealRPM) );
 
         if(wheelsRight.rpm < idealRPM)
             scaledTorque = Mathf.Lerp(scaledTorque/10f, scaledTorque, wheelsRight.rpm / idealRPM );
         else 
             scaledTorque = Mathf.Lerp(scaledTorque, 0,  (wheelsRight.rpm-idealRPM) / (maxRPM-idealRPM) );
 
 
         wheelsRight.brakeTorque = Input.GetAxis("Horizontal") * turnRadius;
         wheelsLeft.brakeTorque = Input.GetAxis("Horizontal") * turnRadius;
 
         wheelsRight.motorTorque = driveMode==DriveMode.Rear  ? 0 : scaledTorque;
         wheelsLeft.motorTorque = driveMode==DriveMode.Rear  ? 0 : scaledTorque;
 
         if(Input.GetButton("Fire1")) {
             wheelsRight.brakeTorque = brakeTorque;
             wheelsLeft.brakeTorque = brakeTorque;
         }
         else {
             wheelsRight.brakeTorque = 0;
             wheelsLeft.brakeTorque = 0;
         }
     }
     
 }