The BMW, which was being driven at a breakneck speed, had rammed into two persons on a motorcycle, flinging them off the two-wheeler last night in the Judges Bungalow area, police said.
Efforts were on to trace the driver of the four-wheeler, who escaped from the spot, they added.
"Forensic experts have visited the accident site and taken vital clues for investigation. As of now, no arrests have been made and efforts are on to trace the accused," Vastrapur Police Inspector M R Sharma said.
Investigators said that the car screeched to a halt after dragging the bike for about 35 metres before ramming into a tree, adding that a youth came out of the car, apologised and got into a car driven by a girl and fled from the spot.
The car, which carried Chandigarh registration number, is owned by a doctor in Chandigarh, police said.