If you can ride your bike 8 miles in 2 hours, you can ride your bike 4 miles in 1 hour. There are 5280 feet in a mile, so you can ride your bike 5280 * 4 = <<5280*4=21160>>21160 feet in 1 hour.
Since there are 60 minutes in an hour, you can ride your bike 21160 / 60 = <<21160/60=352>>352 feet per minute.