GPS error due to 37" tires?

[tec548]

I'm sure some of you guys have run across this. I just put 37" BFG-MT2 on my truck and now the GPS cannot keep track of my position. Apparently it gets off because of the revs per mile difference from stock. I never dreamed that the Ford GPS system would only check the physical position of the vehicle at start-up and about every 20 minutes there after. I knew that the speedo would read about 5% low but this just seems insane. Other than getting the speedo recalibrated for the larger tires is there any other way to correct this? Can this be done? I tried using my programmer to set the correct rev/mile (didn't think it would fix this but wanted to try) and this did nothing for it. Any help would be appreciated!

 

[Bigg50]

NEVER had a problem and this really doesn't make any sense at ALL. There's no way the GPS only checks your position every 20 miles. I'd love to hear how it's able to keep track of turns, stopping and starting, etc while not actively checking your position.

I guess something is wrong with your GPS and it's a coincidence you put new tires on at the same time.

 

[Deletedone]

The GPS should have nothing to do with the size of your tires. Sounds like you've got something else going on. Mine acts screwy when I use the Nav-tv to trick my gps into thinking I'm staying still. Do you have the nav-tv module installed?

 

[Hockster]

GPS means Global Position Sensor its using the sat antenna not your tires rotating.

 

[tec548]

I know it does not make any sense. But if I drive from my house to the highway About 2 miles (straight). It shows me turning about a tenth of a mile early into a parking lot instead of the highway. Then it tracks parallel with the highway (off road) until I take another turn or whatever, but it tracks behind where I am. This only happened the other day when I changed the tires. I have done a complete system reset and lost all my saved points and this did not help either. I don't have a TV module installed. Any other ideas? I have not put my 35s back on but I might just do that to confirm it's not something coincidental that happened.

---------- Post added at 10:49 AM ---------- Previous post was at 10:47 AM ----------

GPS means Global Position Sensor its using the sat antenna not your tires rotating.

Please, I know how it is supposed to work. I'm telling you what it is doing... and I don't understand it.

 

[MajorAR]

Didn't Jackrook have this problem too? I think he took it to dealer and they reset his GPS system or something like that.

 

[LFtrip]

I recall the dealer telling Jackrook it was his tires throwing off his GPS. Thats just a new kind of stupid. It can not be your tires doing it.

 

[BramageDained]

Without knowing the system, it is entirely possible the system compares the two results between wheel rotations(and input from accelerometers/steering input the truck has) and GPS signal to determine distance as a failover should the system drop the fix from the satellites or something. If the two are always different, maybe it gets confused and picks inertial system over gps location.

It's kind of far fetched, but, possible. I've worked on equipment that used GPS and a form of an inertail system for position. When both systems were functional, but, one only had a moderate error(not enough for that system to be ignored) the system sometimes got confused.

Their logic is possible, but, without knowing how the Nav system actually works in our truck it's just a guess based on something that I saw happen in the past.

 

[Jordan@Apollo-Optics]

From what my tuner says (don't know the veracity of the statement), the 37's will mess with the GPS. He said it somehow uses the GPS for speed on the nav but also communicates with your speedo (which will be off).

Basically what BramageDained said is what my tuner said it does. I wonder if it's a 2013-2014 thing with MFT?

Edit: at the same time, my 37's only moved my speedo off by 3mph. I don't think that would be enough to throw the GPS off?

 

[LFtrip]

I just find it strange that my old garmin would track my speed and location perfectly but it wasn't tied into my vehicle at all. Why would Ford make it so complicated when the old technology works fine?