[LAP1DOUG]

For what you want to do, here is the easy way:

1- Place a long straight edge up and down touching the outside of each tire and extending up into the wheel well. Go buy a long rod or small aluminum shape at Home Depot if needed.

2- Measure the distance from the inside of the straight edge to your wheel lip.

3- Try a spacer matching the measurement in step 2. You can probably get away with more than this if wanted as the wheel travel on a stock vehicle will rarely get to the maximum tire overall width, and the supension will gain camber in bump.

Good luck.