rbrais

I'm just going off the experiments others have done.

But yes, when I said "tires" I was referring to the specific mfg. Different tires of the same size have slightly different overall diameters.

etcbrown

It is most definitely affected by the tires. It is not a GPS issue but rather the dead reckoning input and how Ford chose to allow it to affect the navigation system.

And you are not wrong to THINK that, perhaps the designers of the nav system should have spent a little more time doing just that.........THINKING.

jvines

Well I have 295 60 20 trail grapplers and mine is way off since the change. I wonder if the GPS sensor/software was always bad just I didn't notice because the tires kept it close. I'm dropping mine off at the dealer Saturday morning and they say they will reflash the computer and check/replace the GPS sensor.

horak24

Based on everything they had done prior to the GPS unit I have to say it was the sensor. However with all of these other guys having issues and bigger tires its hard to believe it fixed mine.

Psw757

I guess I'm just trying to figure out how best to handle this potential problem. Picking truck up later this week and already paid for the new tires. I'm wondering if I ought to call them and advise them of the potential problem and to see if they recommend a speedometer calibration or if they have some other fix. Shouldn't have to worry about this stuff when your spending this kind of coin.

Psw757

Just spoke with my service manager regarding this potential issue and I was told that there is some sort of sensor that measures tire speed and the data is used for the nav. Was told that as long as it is calibrated to the new tire size the speedometer, odometer and nav should have no issues. This is what I was told they did to correct this issue for some of their customers.

I will post if I have issues when I pick truck up on Friday.

SherpaTroy

I will be picking up my new 2013 silver SC 6.5 FX4 next week, so these comments are from way too much time on this forum, talking with my dealer, but zero from actual problems from my truck...

I checked this with my dealer. We plugged the truck into the computer, and there is a list of tire sizes that can be programed. I don't think you can put in any tire size, only pick from what is available.

I believe that if you change your tires to one of the sizes available in the computer, you should be good. This will change the computer to the same size as the tire you have, and the speedo, Nav.,etc, ... should all be good.

If your new tires are not on the list, change the computer to the size that is the closest. Your speedo should be off by the same percentage as the percent difference between the two tire sizes. The closer you can get, the less everything including the Nav system will be off.

From that list, the two biggest sizes are (1)275/65/18 - 32.2 x 10.9 or (2)315/70/17 - 34.36 x 12.4

My plan was to get 275/65/20 which is 34.05 x 10.9 . This is only 0.84% away from the 315/70/17 size that can be programmed into the computer. With that little variance, everything including the Nav. should work pretty well.

If this does not make sense, and I am not looking at this the right way, please let me know...

HoustonRider

Bingo. Not cause u changed tires.

etcbrown

You sure do think you're the cats meow dude.

The change in tire size is causing this problem for MANY (note I didn't claim it is the ONLY problem across all vehicles) people and it has been proven through actual testing. Not by the paradigms of some stubborn SOB who doesn't understand modern technology.

Please take your sarcastic remarks somewhere else. They only serve to muddy up the waters for people who are looking for answers.

Psw757

That is pretty much what my dealer told me, definitely need a recalibration.

You recall seeing 275/60/20 on the list? I would think that is a very common size.