Be sure that proper chain alignment is maintained when the rear triangle is spread to your desired width. In other words, if the frame is currently at 120 mm, aligned correctly to begin with (not always the case) and you want to go to 130 mm, you need to spread the right side 5 mm to the right and the left side 5 mm to the left to maintain proper alignment. If the entire 10 mm spread is achieved by setting only one side of the triangle, the chain line will be off. Spacer washers on the rear hub and/or funky rear derailleur adjustments will allow some compensation, but it is always best to start with an aligned frame. And align that rear derailleur dropout too (Park tool DAG-2).

Bob (who wishes he had a C&V nickname like all the cool guys do)