Speedometer is WAY off!
Speedometer is WAY off! For some reason my speedometer isn't indicating the correct speed. I originally thought it was the incorrect tire size (215/55/16) that the previous owner had on the car. But when I ran some tire size/speedo error calculators on the internet, they said that my speedo would have been off by only 1 mph or so. So I put the correct sized tires (245/50/16) on today anyway with the hopes of having an accurate speedo. No dice...it's still off as much as it was before. I had my wife drive behind me and I also drove past a couple of those radar speed signs that show "YOUR SPEED" to see what 70 mph equated to on my speedo. 83 mph on my speedo is really 70 mph. What could be the cause of this? The VSS was replaced when my A4 was rebuilt a couple of weeks ago. I checked to see if maybe the rear gears might be different but they appear to be the stock 2.73's. What do you guys think it might be? I don't really want to spend the money on an HPP3 or something else just to bandaid the problem.
My guess is your rear end gears are not stock. The previous owner may have changed it to 3.73 gear and never corrected the computer. What RPMs are you running at lets say 70mph? My 2.73 gears say 1700-1800 rpms.
If your car originally came with 2.73's (meaning the computer is programmed for 2.73's), 70 mph indicated at 83mph would give you 3.23's. Sounds to me like the previous owner grabbed a stock 3.23 rearend out of another F-body and swapped into yours. Reprogram for 3.23's and you should be fine. 
Thanks for the feedback guys. I just went down to my garage and jacked up the rearend to check some things. I first verified whether the rearend was an auburn or torsen. Both wheels turned forward so it's definitely an auburn. Then I made a mark on the driveshaft with a marker and a chalk mark on a tire. I spun the tire one revolution and found that my mark on the driveshaft came around a little over 3 times. You guys guessed it...this thing has 3.23's I guess. Now to find a cost effective device to reprogram my speedo...
Now to find a cost effective device to reprogram my speedo... 
