Derailleur Pulley Wheel Compatibility I can't find replacement pulley wheels for my derailer that are explicitly made for it. Should I be safe replacing them with a set with the same number of teeth ( _i.e.,_ the same diameter) and targeted at the same "speed" chain? I figure the "speed" of the chain would be a good proxy for the axle width of the pulley; is this actually the case? If not, is this difference just dependent on the company that produces the pulley wheel? Should I be safe replacing a Shimano pulley wheel on a ~3 year old Shimano derailer with a current Shimano pulley wheel?

For Shimano derailers, you may be able to find interchangeability information online on Shimano's website, but it's not easy to find. < has "exploded views" of their products which have a handy "interchangeability chart". These seem to be really badly edited though, as I have found quite a few where the interchangeability is mentioned for one derailer but not vice-versa. I think the best way to get a more exhaustive interchangeability list is to just google the "SHIMANO CODE NO." for the part you're looking for, which can be found on the chart in the exploded view of your product. This comes up with a nice list of all the other exploded view PDFs on Shimano's website that include the same part. You can than order the part that goes with any of the products in that list.

This helped me find the exact same pulley wheel I was looking for, however there may be other sources for parts that will work just as well, though they may not be an exact match.