Andy Swarbrick's Scott Foil cycle was taken from the roof rack of his car when it was parked near Roundhay Park on Sunday. He had completed the standard distance age-group event and returned to the park to watch the elite races.
The custom-made carbon frame bike is described as 'irreplaceable' and is black with white and green markings. It is valued at around £5,000.
It was taken from Princes Avenue between 2-3pm.
Anyone who witnessed anything suspicious or who has been offered a bike matching this description for sale is asked to contact police on 101 quoting crime number 13170265103.