Grigg's on the right track, but you must also consider that most tires list the max load at a given pressure, usually between 44-50 psi on low profile tires. You wouldn't want to run that high of pressure as the ride and handling qualities would be very poor. I have seen where a local kid wanted the 225/55/16 on a '72 3/4 ton. He was back within a week with a blowout from insufficient load capacity. The 4 tire together was barely enough for the weight of the empty truck. They also caused problems in the drivetrain from excessive rpm (307, sm465 trans, ans a 4.56 rear) from the tire diameterbeing too small.
Personally, I'd suggest going with the 235/65/17 as they are available in a truck rated tire that can handle the load at a reasonable pressure (35 psi). The 225/55/17 would have to run at 45 to get a close rating, and that is actually lower.
