Dating old bikes
For old Treks, 27.2 is the most common, but for other bikes the diameters can range from 25mm to 33mm.The rear derailleur can often be dated to a year or two by referring to the book "The Dancing Chain - History and Development of the Derailleur Bicycle", by Frank Berto, 3rd edition 2009.This makes dating the components an interesting archeological investigation, but one not necessarily related to the date of the bike. Trek owner Larry Osborn made this observation, and suggested this as a supplementary way of dating a Trek (and other bikes as well).Fueled by this first realization, and with the help of other bike folks, Larry and I have sorted out other codes (a project still ongoing). This Streamliner is owned/restored by Nathan Pence and was painted by Dave Stromberger. The 1937 Roadmaster Supreme is one of the most desirable pre-war bikes.
If you know of other components that are marked or coded that can be added to this list, please let me know.: The information on this page is copyrighted.
The Appendix gives dates of initial manufacture for the vast majority of derailleurs made from 1920 to 1999.
Other manufacturers of bicycle components have date marks on their pieces.
Feel free to quote small parts of the information on this page, but copyright law requires be listed as the source of the information.
In this website, we credit the people involved in the understanding of these codes. (Naturally, for information provided by others, such as for the Campagnolo and Williams codes, the original source should be cited.)Ben writes: "Brakes and brake levers often have date codes on them.