The Stovebolt Site Forums The Shop Area Driveline 1953 3600 - wrong speedometer gear?

My '53 Chevy 3600 with stock 4 speed transmission, stock 4.57:1 rear end and 15" wheels has never read the speed correctly on the speedometer. It is consistently 6-7 mph over the actual speed. I think the wrong speedometer gear was installed in the factory and it has a gear for 17" wheels instead of 15" wheels. What would be the best way to correct this or am I thinking wrong about it? I don't want to change out the wheels and tires just to make the speed read correctly.