Quote Originally Posted by Grog
Some bike mechanics have advised me against WD-40. I think the reason was that it's more likely to damage the plastic parts of your derailleur, and also your tires and other parts of the bike.
Oh, I usually put some newspaper or cardboard to prevent overspray, and do a full wipedown of any areas that may have gotten hit. WD40 shouldn't affect plastic, but it will degrade rubber or anything petroleum based.