Originally Posted by T-Mar

While the underside of the bottom bracket shell is the most common location for the serial number, it can vary depending on the manufacturer and/or year. Other common locations include the bottom and top of the seat tube, rear dropouts and head tube. If there is plastic cable router under the bottom bracket shell, it can sometimes hide the serial number. If you can't find a serial number, we can always resort to component date codes. Thank-you for taking the extra effort. It is very much appreciated.