as a general rule, all guages of any kind tend to be off. Im not sure where exactly I read it, but if you look at the speedo itself, with a top speed of 160, 80 mph should be TDC, but its not. Its slightly to the left. Basically, that results in a calabration thing that causes the speedo to read higher than the actual speed.
<span style='color:gray'><span style='font-family:Courier'>1995 e36 3 Series RIP
1999 e46 3 Series BURN IN HELL
2000 MR-S Roadster= Current</span></span>