Originally Posted by DockingPilot
Well it is definitly off. 3 miles every 100. And now 8.8 miles low when approaching the 300 mile mark comapred the 276c readout. Looks like it will click -9 at 300.
Do you fellas think the tire could be the reason ?
Yes, it most likely is the prime cause. Also, remember that no matter what tire you run, it will change as it wears. Therefore, it will become smaller in diameter as it wears.
A 140/80 measures out to a height of 112mm. A 150/70 measures out to 105mm. This, of course, is having all things equal in terms of radius, profile, etc.within the tire design.
Don't forget your GPS isn't dead nuts accurate. It can lose signal from time to time along with other issues.
All in all, it's close enough so don't over analyze it. Just ride it.