How do the frame numbers on GT frames work.

I once read somewhere on the early ones they were under the bottom bracket andthe numbers reffererd toa date? Is that the case ?

Usually a letter followed by numbers on the BB or rear dropouts. The number after the letter is generally the year. G56983 would be 1985. May not be the case with earlier GT's (83 and prior.)

how old is the bike(genral idea) and whats the serial number?

it depends on where the frame was made - USA, japan or taiwan.

USA is on the rear dropout, is all numerals and the first 3 or 4 digits are the month/year (ex:283xxxx would be february 1983 or...1186xxxx is november 1986). these may also have a number or letter/s that indicate the model near the serial.

the "G5" number above is a japanese number and can be on either a dropout or under the BB.

taiwanese numbers are under the BB, usually have several letters towards the beginning and are longer than USA or japanese numbers. they are not always obvious with the date code.

[ January 06, 2006, 10:11 PM: Message edited by: mr coasterbrake ]

post a pic and tell me the serial number, and i will tell you what it is!