you have to remember it doesn't factor in traffic or anything like that, and I think it's based off of average speed for the trip, which is pretty reasonable because that takes the traffic into account without "knowing" the traffic conditions. Plus if I drive signficantly over the speed limit or under the speed limit it will be fairly close. I had a drive from Tampa to Jacksonville that was only about 10 minutes off.

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2006 BMW X5 4.8is Lemans Blue/Beige/Dark Maple
-Nav, Comfort Seats, Heated Steering Wheel,
Rear Airbags, AUX Input
2009 BMW M3 Space Grey/Black/Carbon
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