Auto tuner needed with 240tire?

Here's my experience with gps and speedos - I've driven in my truck and car with the gps, and they both seem to match the speed shown on the gps. I've also rode my previous bike ('05 ninja with a digital speedometer readout) and my Stryker with the gps. Here's what I noticed with both of the bikes - at slower speeds the speedo read a couple mph over the gps reading. As I went faster, the gap between the speedo reading and the gps reading got larger. For both bikes, when the gps read 75mph on the freeway, my speedos on the bikes read 83mph. Again, no answers, just my experience.

Well, not to sound like an ass but that's pretty obvious. The calculation is a ratio and therefore is more distorted at a higher speed (higher number).
Eventually I see GPS technology being used for speedos. That way, your speedo would always be accurate no matter what tire size, or other modification done to the vehicle.
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I realize the math is obvious, mainly just pointing out that it was off on the bikes, not the other vehicles