The true speed is up to 10% off, so the speedometer never reads below "true" speed. The true speed can be displayed in the On Board Computer (OBC) by pressing reset in AVG SPEED mode. A BMW technican stated this in the June 2001 Roundel. Nice to know. So, next time your doing 140 mph in your 4.4i let me know the "true" speed if you are daring enough to take on hand off the wheel. :)