The collision happened on the A27 at Patching between the Coach and Horse pub and the junction of the A280 shortly before 8pm on Sunday evening, police said.
The cyclist, a 77-year-old man from Goring-by-Sea, suffered a serious head injury and was taken to the Royal Sussex County Hospital in Brighton.
Later that evening, his condition was described as stable and not life-threatening, police have said.
The driver of the Peugeot Boxer 290, a 73-year-old woman from Braintree, Essex, was not injured.
The westbound carriageway of the A27 was closed while the incident was dealt with and reopened at 11.30pm.
Anyone who witnessed the collision is asked to email [email protected] or call 101, quoting Operation Gainsford.
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