Can you use a list? You may need to include this:
using System.Collections.Generic;
//Somewhere in the class
List<Wheel> myWheels = new List<Wheel>();
// In your method
var _wheel = new Wheel();
// Set your properties
myWheels.Add(_wheel);
//Then when needed, you can loop like this:
foreach(var wheel in myWheels)
{
// do something with wheel...
}
I don't do XNA, but this is fairly common in C#.