Programming for Larger Tire Size

brnc_o_vrlndr
Aug 15, 2020
Moderator

Rank VI

Aug 15, 2020

So, I have never owned a vehicle that was capable of programming the cluster (or other module) to correct the speedometer/odometer for larger tire sizes. I have either lived with the speedometer offset or re-geared the differentials to correct the power loss and speedometer offset.

That being said, I am really hoping, first of all, that we will be able to select the 4.7 final drive without the Sasquatch package and, second, it will be an easy process to program for larger tires.

What has your experience been with installing larger tires on other vehicles? How easy has it been to program the module and are there limitations to what tire size you can program? Or is it just adjusting the programmed ratio until the speedometer is close to accurate?

Thanks, everyone! It's fun thinking through some of these issues, but we obviously won't know for sure until the build tool is out and people can start getting their hands on one.
"Of all the paths you take in life, make sure a few of them are dirt" - John Muir
"The mountains are calling, and I must go..." - John Muir
BN #0120
Deano Bronc, Commodore
Last edited by a moderator: Aug 15, 2020

Rank VI

Aug 15, 2020

#1
So, I have never owned a vehicle that was capable of programming the cluster (or other module) to correct the speedometer/odometer for larger tire sizes. I have either lived with the speedometer offset or re-geared the differentials to correct the power loss and speedometer offset.

That being said, I am really hoping, first of all, that we will be able to select the 4.7 final drive without the Sasquatch package and, second, it will be an easy process to program for larger tires.

What has your experience been with installing larger tires on other vehicles? How easy has it been to program the module and are there limitations to what tire size you can program? Or is it just adjusting the programmed ratio until the speedometer is close to accurate?

Thanks, everyone! It's fun thinking through some of these issues, but we obviously won't know for sure until the build tool is out and people can start getting their hands on one.
Wow!
A way to calibrate the instrument cluster for larger wheels is a novel idea. How about it ...Ford engineers?

Rank IV

Aug 15, 2020

#2
So, I have never owned a vehicle that was capable of programming the cluster (or other module) to correct the speedometer/odometer for larger tire sizes. I have either lived with the speedometer offset or re-geared the differentials to correct the power loss and speedometer offset.

That being said, I am really hoping, first of all, that we will be able to select the 4.7 final drive without the Sasquatch package and, second, it will be an easy process to program for larger tires.

What has your experience been with installing larger tires on other vehicles? How easy has it been to program the module and are there limitations to what tire size you can program? Or is it just adjusting the programmed ratio until the speedometer is close to accurate?

Thanks, everyone! It's fun thinking through some of these issues, but we obviously won't know for sure until the build tool is out and people can start getting their hands on one.


Well in general most Fords don't allow for tire calibration over 35", so any larger tire results in an inaccurate speedometer/odometer. Good news is if Ford is producing a 2" lift and 37" tire option, the BCM value (module controlling tire size via ForScan) for the speedo calc can handle at least 37" tires.
brnc_o_vrlndr, Commodore

Rank VI

Aug 15, 2020

#3
Well in general most Fords don't allow for tire calibration over 35", so any larger tire results in an inaccurate speedometer/odometer. Good news is if Ford is producing a 2" lift and 37" tire option, the BCM value (module controlling tire size via ForScan) for the speedo calc can handle at least 37" tires.
Cool deal....
Ford engineering can do this...
Moderator

Rank VI

Aug 15, 2020

#4
Well in general most Fords don't allow for tire calibration over 35", so any larger tire results in an inaccurate speedometer/odometer. Good news is if Ford is producing a 2" lift and 37" tire option, the BCM value (module controlling tire size via ForScan) for the speedo calc can handle at least 37" tires.
Thanks. I’m hoping that is the case. They have to know that people will fit as big a tire as possible. Of course, re gearing will help with that calibration.
"Of all the paths you take in life, make sure a few of them are dirt" - John Muir
"The mountains are calling, and I must go..." - John Muir
BN #0120
Commodore

Rank VI

Aug 15, 2020

#5
Thanks. I’m hoping that is the case. They have to know that people will fit as big a tire as possible. Of course, re gearing will help with that calibration.
You can otherwise use forscan and change the ratio for tire size. I did that with my GT350 when I went to GT350R spec tire sizes. They were 1/2” diameter smaller and it speedo off enough to annoy me. I want it right on. It doesn’t void anything as it’s not a tune. It’s just tweaking the as built file so the BCM (body control module) can adjust. The trick is calculating the new hexadecimal number to enter in. On mustang6g they had a whole thread about it. You need a PC, a OBDII to WiFi adapter and the forscan software which is free. I am hoping Ford does build in a selection option to set the tire size though given the range of sizes these vehicles will have depending on what the owner buys. At least give the Ford garage the tools to do it if not. Ford service is clueless to change this in other cars. I had tried that route first with my GT350 to no avail.
Deano Bronc, brnc_o_vrlndr

Rank VI

Aug 15, 2020

#6
You can otherwise use forscan and change the ratio for tire size. I did that with my GT350 when I went to GT350R spec tire sizes. They were 1/2” diameter smaller and it speedo off enough to annoy me. I want it right on. It doesn’t void anything as it’s not a tune. It’s just tweaking the as built file so the BCM (body control module) can adjust. The trick is calculating the new hexadecimal number to enter in. On mustang6g they had a whole thread about it. You need a PC, a OBDII to WiFi adapter and the forscan software which is free. I am hoping Ford does build in a selection option to set the tire size though given the range of sizes these vehicles will have depending on what the owner buys. At least give the Ford garage the tools to do it if not. Ford service is clueless to change this in other cars. I had tried that route first with my GT350 to no avail.
Cool
First I’ve heard of the Forscan tool...
Thanks!

Rank V

Aug 15, 2020

#7
Wow!
A way to calibrate the instrument cluster for larger wheels is a novel idea. How about it ...Ford engineers?
Not really, you could do it on the 5th gen broncos too.
Commodore

Bronco guy doing Bronco-ey things with his Bronco

Aug 15, 2020

#8
There are a number of tuning tools that can make these changes as well. Should be easy to find someone to make the necessary changes when the time comes!
First Edition 4dr
1967 Bronco
1993 Mustang Notchback
DRWright, brnc_o_vrlndr

Rank VI

Aug 16, 2020

#9
There are a number of tuning tools that can make these changes as well. Should be easy to find someone to make the necessary changes when the time comes!
Used to. Not with the Ford BCM. You used to be able to change tire sizes or gear ratios with hand held tuners used for flashing engine tunes. The Speedo is now controlled via the body control module (BCM) and the tuners only interact with the ECM. Back on my 2011 Mustang I still had tire size capability or gear ratios. On my 2017 GT350 it went away.
DRWright

Bronco guy doing Bronco-ey things with his Bronco

Aug 16, 2020

#10
Used to. Not with the Ford BCM. You used to be able to change tire sizes or gear ratios with hand held tuners used for flashing engine tunes. The Speedo is now controlled via the body control module (BCM) and the tuners only interact with the ECM. Back on my 2011 Mustang I still had tire size capability or gear ratios. On my 2017 GT350 it went away.

Dude, that isn't even close to correct. I use my HPTuners module to make those changes regularly (a recent one was a 2016 F150 which had lower gears installed). You can do these changes with all kinds of devices, like Ngauge, even free software like Forscan.
First Edition 4dr
1967 Bronco
1993 Mustang Notchback
DRWright

Rank 0

Aug 16, 2020

#11
At a dealership level,I can reset for tiresize within ford tire sizes availiable from factory,on the lifted vehicles with tire upsizes I use Forscan to calibrate.Word of caution you will be changing factory hex codes and if done incorrectly can be detrimental to vehicle operations.
brnc_o_vrlndr

Rank VI

Aug 16, 2020

#12
Dude, that isn't even close to correct. I use my HPTuners module to make those changes regularly (a recent one was a 2016 F150 which had lower gears installed). You can do these changes with all kinds of devices, like Ngauge, even free software like Forscan.
Well maybe the 2016 F150 still allowed it but the 2015+ mustangs system did not. The new control scheme with the ECM & BCM does not. I am well versed in tuning. I was tuned with the GT350. Used an Nguage and Lund Racing. It’s not doable in a tuner on the newest stuff Ford is doing which I expect we will have in the new Bronco. I am well aware of forscan if you read several messages up I posted about that tool. In my 2011 Mustang I was able to adjust in the SCT tuner but again, not in the newest mustangs. The 2016 truck is older as well so you can’t use that as a comparison. Ford is changing the control schemes on there newer platforms.

Rank IV

Aug 16, 2020

#13
On 2011-2016 Super Dutys and F series through 2019 you couldn't put in tires over 35" with ForScan and have the vehicle work correctly. You'd get a series of RSC and Axle ratio errors. Even modifying rotations per mile for the wheel wouldn't help the problems. Hope the BCM mappings have changed for the Bronco (which they must if the factory offers 37's at any point).
brnc_o_vrlndr

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