Anybody know if the tire size adjustment through the setup screen affect the spedo only or does it also account for accuracy in the Navi?
When you're in an underground garage the pointer still moves thanks to a compass and what I assume to be a distance meter of the tires.
Could changing the tire size affect the accuracy of the Navi?

 

The pointer moves in a garage owing to inertial sensing. Intertial sensing knows nothing about tires. It only know motion in 2 or maybe three axes and it use this and, I presume, the last GPS fix to subtract out earth rate to figure out how much the vehicle moved in what direction. In addition, accelerometer(s) are typically used to sense rotation rates about these axes. These are used to figure out heading. It seems likely that they sense delta v in X and Y for inertial position and delta theta about the yaw axis for heading. They probably don't waste money on sensing the other axes for rotation rate or inertial velocity since they'd only be relevant if, say, they wanted to detect rollover of the vehicle or tumbling off a bridge.

 

Oh, I'm betting the tire size setting has to do with the trip computer functions which for the TL are pretty much NA.

 

Whaaaaaat you say? Hahahahahha.

My guess is that you just meant to say, "No, tire rotation has not affect."

Perhaps you could repeat that in layman terms?

 

Those are layman's terms.

The bottom line is that I don't think the tire size setting has anything to do with the navigation displays. I believe they use some cheap components that are common to inertial navigation systems to figure out the vehicle heading--which way the nose points--and motion (left, right, forward, backward) over short intervals and in the abscence of updated position fixes from GPS.

I'm guessing the tire size data is used by trip computer functions for things like distance travelled--counting revs is easier than integrating INS or GPS fix information--and derivatives like fuel consumption as a funciton of distance.