Chrome discoloration on cycle accessories

A. Chrome should not discolor except possibly due to extreme heat (exhaust pipes), Jim. Are you sure these components are actually chrome plated rather than just something shiney?

A. Jeffrey Holmes suggested on a similar letter that the yellowed areas may lack chrome plating, and the underlying nickel is tarnishing -- this sounds possible. Frequent waxing is the only defense against the yellowing if chrome is missing.

A. You are seeing the nickel that was under the chrome. You said the areas of tarnishing seem to be getting larger. You also said you clean and polish your chrome regularly. In some circumstances I have seen parts that were cleaned and polished so much that they rubbed right through the chrome. Good chrome should never need polishing. Just a gentle wash with soapy water or glass cleaner followed by waxing. If you use something that says it is a polish, it will most likely be too abrasive. Every time you polish your part more chrome is removed and more nickel is exposed.
There is the possibility that you may not have gotten good chrome in the first place. Lately I have had more customers bringing me parts that seem to have suffered the same fate. These parts are mass produced which makes them inexpensive but sometimes quality suffers. And, of course, they will never compare to items that are custom plated at a good chrome shop.
If you want parts that are more durable and better looking, take them to a quality custom plating shop that has a good reputation. You will pay more but have fewer regrets down the line.