Okay, here's the situation; I've put a big-block in my cars a few years ago. Speedo is off. Changed the rear end gears, speedo off some more. I had 14" wheels and changed to 15". I have changed the gear on the speedo cable and have the speedo reading about 10 mph fast. Being that I have a C-6 trans, the drive gear is part of the output shaft. I can get the speedo closer by putting taller tires on the back. To get the speedo the closest, I need to put on P235/75/15 tires. This size just doesn't look right and there is some clearance problems. Anybody have any suggestions on how to get my speedo to read correctly.