Dating in the 1980s everything dating book
Especially useful, and challenging to sort out and verify, was the Shimano code.Also gathered on this page are date codes decoded and generously provided by others.Of course, all this assumes the bike has the original component.The most likely components to be original are the stem, handlebars, seatpost, and brakes.Pull the lever and look inside the top of the lever arm for a code such as "1084." Dia-Compe extension levers (yuck) also tend to have date codes on the side that faces the brake hood.I have a set of Dia-Compe mountain levers where if you pull the lever all the way, a piece of the lever is exposed, which has a clock-type date code.Swaps also can be made as the bike falls out of favor, or is being sold, where the higher quality components are traded for lower quality ones that the owner had onhand.(Don't all cyclists have boxes and boxes of old components in their garage?
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.
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.
The rear derailleur freewheel/cassette and chainwheels are probably the first to be changed on a bike.
On a vintage bike in excellent condition (that apparently had a lonely existence in a garage) all of the components likely are original.