Originally posted by Grant Eaton
So when my odo reads 65 MPH, I'll really be going about 66.6 MPH.

No one else has commented about the fact that having an inaccurate speedometer changes the behavior of your airbag deployment and possibly ABS. If your big tires are 8% off, that's a pretty significant piece of false data to be feeding your life-safety system.
Another thing that no one has mentioned is that speedos aren't all that accurate from the factory anyway. One of the big car magazines always used to test their accuracy as part of the road test and they almost never were right. The were also almost always reporting the speed too high (presumably to keep the drivers 'out of trouble') so by putting bigger tires on your truck you very well might have made your 'instrument' MORE precise. In fact maybe you should have gone for the '60's. ;-]

As far as the airbag, I think the line beween it going off and not going off is around 15 miles per hour isn't it? At that speed 8% is only 1 or two miles per hour so I think I can take that risk. Besides I think that they measure your speed of collision by measuring the force of the decelleration with their sensors, not by tapping into the speedo.