Large tires
More Turbo
Joined: Feb 2006
Posts: 538
Likes: 11
From: Shiner, TX
I think the dealership can reprogram up to 35" tire size.
But when it comes to the TPMS in these newer trucks, they can not mess with that for fear of a government fine, the sky falling, or whatever the excuse is. The best advice we have at this time is to make sure the new set of tires has a sufficient load rating and can handle the minimum recommended tire pressure before purchasing tires. Which gets difficult with over-sized tires, I know.
But when it comes to the TPMS in these newer trucks, they can not mess with that for fear of a government fine, the sky falling, or whatever the excuse is. The best advice we have at this time is to make sure the new set of tires has a sufficient load rating and can handle the minimum recommended tire pressure before purchasing tires. Which gets difficult with over-sized tires, I know.
BuhBye F450, I'm relaxin'
Joined: Feb 2009
Posts: 1,288
Likes: 19
From: Plainville, MA
Correct!
That is correct but it's not very straightforward either. The dealer is given a list of actual tire sizes to choose from, not diameters. I had to write down what their choices were, then get online and look up those sizes to get the diameters. I don't remember what we actually chose but the 35" diameter was the tallest available and turned out to be a weird, tall, skinny tire in the list.
It also has to be changed in three different modules in the truck's software - one handles the speedometer, one handles the collision computer (braking force due to the added diameter and weight) and one for the transmission I believe. A good Ford Diesel mechanic should know where - if I can find my original info, I'll post again.
It also has to be changed in three different modules in the truck's software - one handles the speedometer, one handles the collision computer (braking force due to the added diameter and weight) and one for the transmission I believe. A good Ford Diesel mechanic should know where - if I can find my original info, I'll post again.
Junior User
Joined: Oct 2010
Posts: 59
Likes: 0
From: Chicago
That is correct but it's not very straightforward either. The dealer is given a list of actual tire sizes to choose from, not diameters. I had to write down what their choices were, then get online and look up those sizes to get the diameters. I don't remember what we actually chose but the 35" diameter was the tallest available and turned out to be a weird, tall, skinny tire in the list.
It also has to be changed in three different modules in the truck's software - one handles the speedometer, one handles the collision computer (braking force due to the added diameter and weight) and one for the transmission I believe. A good Ford Diesel mechanic should know where - if I can find my original info, I'll post again.
It also has to be changed in three different modules in the truck's software - one handles the speedometer, one handles the collision computer (braking force due to the added diameter and weight) and one for the transmission I believe. A good Ford Diesel mechanic should know where - if I can find my original info, I'll post again.
I work for Ford/Land Rover and just changed my tire size on both my f250 and a customers land rover. We can change it by tire size for land rovers and rev's per mile on ford's. I have access to Both IDS and the old WDS from ford. And we can only adjust it to a certion size.
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Junior User
Joined: Oct 2010
Posts: 59
Likes: 0
From: Chicago
If you want to go bigger then 35's then you need to get a hand held tuner so that you can adjust it for yourself.
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BuhBye F450, I'm relaxin'
Joined: Feb 2009
Posts: 1,288
Likes: 19
From: Plainville, MA
My Original Post...
I found my original post - I was with the Diesel Tech when he did it so I got to see the various windows he navigated through. Here's the post:
I've since upgraded to 37's so it's off again - I'm STILL waiting for SCT to update my TSX so I can fix it with that... that function is currently not available on their "State of the Art" tuner! 
I just got home from my dealer after having my '08 done and there were 3 places they had to change the size. The first module he went into under "Tires" had one setting for "PCM" and another for "ABS". He couldn't plug in a random number - only pick from a list. My 35's have a "revolutions per mile" of 598. The closest (and largest tire diameter) available was a "285/95R-18" which had a rpm of 596. We picked that for both "PCM" and "ABS" and saved it. He backed out and there was another module that said "Tires/Axle Ratio" - he went into that and everything was populated except the "tire rpm" - he again selected that "285/95R-18" tire and hit save. My speedometer/odometer is now correct as well as shifting points, braking, etc. I don't know if the software is the same for earlier models but that's the procedure for '08 - '10 trucks. Hope this helps!
I've since upgraded to 37's so it's off again - I'm STILL waiting for SCT to update my TSX so I can fix it with that... that function is currently not available on their "State of the Art" tuner! 
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Tahnka
Pre-Power Stroke Diesel (7.3L IDI & 6.9L)
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Oct 7, 2010 04:58 AM
