A dark blue Honda motorbike collided with a red Honda motorbike near layby 7 on Victoria Avenue at around 12:10 on Sunday (28 May).
One of the riders was injured and taken to hospital.
Police have issued an appeal for footage of the incident from spectators and riders who attended the event, which is organised by Holidays for Heroes Jersey.
Anyone that may have any footage is asked to contact the States of Jersey Police on 612612 or make an anonymous report via independent charity Crimestoppers by calling on 0800 555 111 or using their anonymous online form.
