I'm finishing my drivetrain swap with a turbo2 diff and was talking to a friend who said to make sure to put a compatible VSS or my speedometer will be inacurate. I hadn't seen anything about this before... Thoughts?

 

If the rear end ratios are different. The only ratios that are different are the convertibles, automatics, and GTUs's. If you swapped this TII drivetrain into a Non-GTUs/vert/auto body, then you have nothing to worry about.

 

S5 convertibles have the same 4.10 but open as the TII. It's the S4 Verts that have the 3.9. There is no "vehicle speed sensor" on our cars unless you have ABS, which still won't do anything in regards to your speedometer.

The transmission has the mechanical gearing that turns your speedometer cable and hooks up to your speedometer. Regardless, like AGreen said, if you did full transmission/diff swap, don't worry about it. And if you didn't, it will be off somewhat if you went to a different final drive gear. Heck, if you have bigger wheels in your car than factory your speedometer is already off.