Interesting... I just talked Boardwalk Porsche service in Plano, Tx. They don't calibrate speedos, and the service mgr acted surprised that mine is 5 mph off from my GPS. He said "well, you haven't got any speeding tickets yet, have ya? ...then that's a good thing." (that was a bull**************** answer)
He asked me if I had non-factory sized tires. He seemed to act "unaware" of this issue, and didn't even question the accuracy of my GPS
hmmmm. He then referred me to some other business in Richardson, Tx called Zebco (not the same fishin pole guys)
I think Porsche knows about it, and they don't have a fix for it. Now I get the runaround to a 3rd party business. I'd sure like to know exactly how fast I'm going and not have to add/subtract before I hit the cruise control, I only use my GPS when I need it. Everything about this car is nice, but the speedometer is crap!