Is your front shifting indexed? If so then the wrench's comments about chain rub is partly true, sometimes. Without the ability to minutely position the ft der cage so to not rub on the chain (as an indexed system is when no trim feature is present in the lever) the manufacturer of the der instead depends on the cage's shape/contour and minimal tolerance of the system.


So if the rings are slightly bent, if the chain has any side ways waviness, if the spacing between the rings is not spot on, if the der's alignment isn't just right, if the limit screws aren't set right, if cable "tension" isn't right and if the rider insists in using cross chaining cog/ring combos then some rub is likely to be present some of the time. Even with a "perfectly" speced and set up system some rub can happen with the bike's flex.


When front indexing first came out Shimano printed a small instruction sheet pictorially describing the gear combos where rub was acceptable. That few ever got this slip of paper with their new bikes and that this is no longer published (or included with new bike packets) says a lot about both the buying public's and the industry's acceptance of some chain rub sometimes as being the norm. Andy