When you built your EZ or your Defiant, you should have set the axles on the main gear such that your main wheels were toed in about 1/4' on each side. If you have noticed excessive tire wear, inside edges or outside edges, it is time for you to check and possibly adjust the main gear alignment. With an already completed airplane, probably the easiest method of checking this is as follows: Load the airplane to the same load that you normally fly.
Now, pull the airplane at least 100 feet forward on a smooth concrete or blacktop surface. This will allow the gear to spread to its normal position, the wheels will be in their natural position for this weight, and this is the condition you want to check the wheel alignment. Using a plumb bob or level, drop the aircraft centerline to the ground (center of the nose, center of the spinner tip), snap a chalk line between these two points. Use a 36" straight edge (hardware store, aluminmun yardstick) and hold it so that the center of the 18" mark is at the axle centerline.
Hold the straight edge against the wheel rim (or tire, if fat tires are used]) and measure from each end of the 36" straight edge to the chalk line aircraft centerline. Record these dimensions and repeat on the opposite wheel. Ideal or perfect results would have (See Diagram) A=A2, B=B2 and A+A2 B+B2 or slightly less. When A+A2 = B+B2, then the main gear toe-in is zero which is probably the perfect situation for tire wear, but 1/4' of toe-in, that is A, would be approximately .080 smaller than B and A2 would be approximately .080 smaller than B2, would be best for ground handling and straig7t tracking. Measuring to the airplane's centerline lets you know if you have the gear on straight but, realistically, it is not critical if your A and B dimensions are not identical to your A2 and B2 dimension. Wow, hopefully you are not all too confused by the above!
Remove your axles and use metal taper shims (available from Aircraft Spruce or wicks) or build up the gear leg with glass and grind to set your axles to meet the above dimensions (you also must use 36" straight edges or the dimensions will be different for the same angle!). Once you have the correct toe-in set, you will notice an improvement in tracking, shorter take-off and less tire wear' Go for it!