Wife's car is off about 3 mph at 80 so that's almost 4%.

Decimal of 15 could be 1.5% almost seems like why bother.

240 could be 2.40? That seems more probable.

What have your measured for the real vs apparent speed on your X5?

Weird on BMW to do this. My other cars mostly had acutlal speed speedometer. I would do timed miles occasionally to confirm my speedo was accurate back in the pre gps days.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)