GPS error due to 37" tires?

[BramageDained]

My guess would be so that the Nav would mostly still work if there was an issue with the GPS signal/antenna/wiring.

 

[The Car Stereo Company]

it doesnt make sense. if its only off by a little bit, wouldnt it get worse the more you drive? i dont see how it could be off by a little bit and then stay that way. the more you drive, the further off it should be. for example, if you have 2 straight lines and one line is off by 1 degree, the distance is minimal at 10 ft. well if nothing changes, whats the difference at 100ft? 1,000ft? if it was the tires, wouldnt it continually throw it off until the distance was so great that it would be in another state? i dont see how it could be a tire issue, but you never know. i could (and most likely) be wrong. it just doesnt seem logical. it seems almost like a radio or antenna problem.

 

[tec548]

I think this is exactly what is happening. I put my 35s back on and went for a ride and all was good. What a great big piece of pooh this is. Does anyone know of a way to either correct the speedo via software or have the GPS disregard the trucks speedo input?

Yes, I forgot who asked it, but it does continually fall behind for about 20 minutes then corrects itself to the actual position and begins falling behind again. According to the GPS I have driven completely across Lake Conroe... twice! After TRR I know the truck is capable of more than what I thought but floating is not an option.

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 ignore 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.

 

[BramageDained]

it doesnt make sense. if its only off by a little bit, wouldnt it get worse the more you drive? i dont see how it could be off by a little bit and then stay that way. the more you drive, the further off it should be. for example, if you have 2 straight lines and one line is off by 1 degree, the distance is minimal at 10 ft. well if nothing changes, whats the difference at 100ft? 1,000ft? if it was the tires, wouldnt it continually throw it off until the distance was so great that it would be in another state? i dont see how it could be a tire issue, but you never know. i could (and most likely) be wrong. it just doesnt seem logical. it seems almost like a radio or antenna problem.

Maybe the system only polls the GPS on a given interval. So right at that point it would correct to GPS position, then run off the sensors on the truck until the next polling period.

The system also tries to correct you to be on a road. There's one spot near me that has an interchange right after an underground tunnel. Sometimes, if you lane change while in or just past the tunnel, the system will "correct" itself and think you're on a side street that is parallel to the freeway. If you stay in one lane(even the far right lane) it never happens.

The side street is probably 50' from the freeway.

If you miss your turn on a non-cloverleaf interchange, it keeps plotting your course like you took the exit for a few seconds. Then, it figures out you were wrong and recalculates.


Since I've never tried/noticed, does the Nav freak out if it goes for a certain amount of time without a GPS signal? I've not been in the previously mentioned tunnel for more than a couple minutes, SiriusXM will cut out, but, I've not noticed the Nav saying it doesn't have a GPS signal.

 

[Fred]

I think this is exactly what is happening. I put my 35s back on and went for a ride and all was good. What a great big piece of pooh this is. Does anyone know of a way to either correct the speedo via software or have the GPS disregard the trucks speedo input?

Yes, I forgot who asked it, but it does continually fall behind for about 20 minutes then corrects itself to the actual position and begins falling behind again. According to the GPS I have driven completely across Lake Conroe... twice! After TRR I know the truck is capable of more than what I thought but floating is not an option.

That is interesting.... (Tin foil hat on) I wonder if this is a way for Ford to collect driver data and changing tire sizes messes with the 'spyware'...

I would be VERY interested as to if there is a connection and if so why?

 

[Huck]

GPS always knows your lat Lon position, under the "where am I" button


Sent from my iPhone using Tapatalk

 

[Fred]

GPS always knows your lat Lon position, under the "where am I" button


Sent from my iPhone using Tapatalk

Yeah, but what do they do with the information....if nothing else a marketing gold mine...

 

[The Car Stereo Company]

set off an airbag and see where the ambulance responds to. at least you will know if it really is off by a bit.........

 

[Fred]

set off an airbag and see where the ambulance responds to. at least you will know if it really is off by a bit.........

Lol...expensive test....

 

[Red]

Just take it to the dealer and have them recalibrate your speedo to the new tire size. They hook it up to a laptop and drive around to calibrate. It cost me $80 to have it done on my last Ford.