Unlikely. Both are measuring in miles/tenths-of-miles, and a difference of 18% would be more than data set resolution would provide.

I have great faith in Google's distance measurements. I have mapped bicycle rides on Google, then compared the distances against a calibrated odometer on my bike that measures to the 1/100th of a mile, and found errors of less than 100 feet in a 20 mile ride. That's 99.9% accuracy, a far cry from the 18% difference between Garmin and Google.

The GPS in my Honda shows a distance of 1996 miles for the trip, but I haven't checked to see the actual route it chose, so it may be Apples and Oranges comparison.

tanstaafl.