The collision, involving a pedal cycle and a Land Rover, occurred at about 3.30pm on Saturday 10 October 2015, on the A59 at the Carlton junction near Broughton Hall.
A man in his fifties, from the Skipton area, was riding along the A59 towards Skipton when he was involved in a collision with a blue Land Rover Discovery towing an Ifor Williams trailer.
The Land Rover was in the process of overtaking the cyclist when the collision occurred.
The cyclist was taken by Air Ambulance to Leeds General Infirmary, where his condition is described as serious. The Land Rover driver, a man in his sixties from the Keighley area, was not injured.
The road was closed for about six hours while police investigated the scene of the collision.
Officers are asking for any witness who saw either the cyclist, who had been riding with two other cyclists prior to the collision, or the Land Rover and trailer, to contact them. Please dial 101, select option 2 and ask for the Major Collision Investigation Team, quoting reference number 12150179799.