FORScan forum

Hi, I have a F150 2010 and I would like to adjust tire size but I can't see any post that help me. Could you said me which is the correct line of BCM to change my tire size?.

I use this aplication: https://docs.google.com/spreadsheets/d/ ... 2133040050
The result number is xxxx 09C0 xxxx (285/55 r20)

Thanks a lot for your help.

I tried the circumference setting after changing tire size my speedo went from 2-3 mph slow to 3-4 mph fast.
I put on a factory size tires 275-60-20 can someone out there with this size tire from the factory tell me what circumference setting was your preset???

I have stock 2019 Raptor wheels(315/70/17) on my 2014 F150. When I calculate my tire size in mm I get 2741mm, but when I set the tire size in the BCM to 315/70/17 it make the Tire Circumference to 2652. Am I doing something wrong? My speedo is 5 mph fast compared to my GPS.

Edit: Forgot to say, It's also not letting me run the PCM relearn test, it keeps saying its interrupted but I can't tell whats going wrong.

Enter the 2741 where it shows 2652 and then hit write and remove any dtc's and then do a relearn.

McJanDK wrote: Tue Mar 09, 2021 9:17 pm you have to x0,967 to get the correct data in mm after calculation... like mine 205/45R17 = 1935x0,967=1871 and this is for ford Fiesta MK8 from 2020
I enter 1870 and then its worked

Hello. Why 0,967 ? It seems ok for my C-Max 2017 because 215/55x16 is 2019mm but 2019x0,967 = 1952 and original parameter in Forscan is 1955.

I just did mine but I used the spreadsheet for actual mph vs speedo mpg. I replaced stock 20" (can't remember tire size, basically a 32" tire) with 285/75/17 which is a 34" tire. At 70mph on speedo, I was actually going 73.
Used spreadsheet to calculate new bits in and set them. Changed to 70 on speed was like 65 or something actual, way overcorrected.
Entered the 70/73 BACKWARDS in the spreadsheet (73 in the speedo field, 70 in actual speed field), used that bit setting, and now it is spot on.
I think this method is the most accurate, because it by default accounts for any squish. I didn't know about the tire circumference setting, or I would have checked it before and after to see if it changes with the bits update.
Unfortuatly I do have the DTCs which I can't clear.

Trying to decide if I should leave as is, or set back to stock to save a few miles on the odo...
I'm sure I have to re-adjust the miles to empty (MPG adjustment factor).

So, basically I think I have the same problem as most of you who are having tire size issues. I have the most updated version of Forscan (v.2.3.42). I have a 2016 F-250 with a 2" lift. It has Nexen 35x12.50R20LT Tires. I have a transmission shudder between 40 and 50 mph, basically when the transmission is under load like going up a small hill just before hitting overdrive. My mechanic changed my fluids etc and thinks that my shudder is a result of the computer reading one tire size and the ratio to the transmisison, etc. When I look at Forscan, there are several modules in which I see Tire size affects something else. I have converted my tire size to mm (2791) and input that into the BCM. When I do, i get a "Service Stabilitrak" error message and I can no longer turn off traction control. Does anyone else have any experience with this issue or transmission shudder that they think may be related to tire size?

alzev wrote: Fri Jul 09, 2021 12:36 am I have followed this and every other link related to properly updating my tire size. I have 2021 f150 lariat power post and can’t seem to get it dialed in. I downloaded the spreadsheet that someone had spent a lot of time making and plugged in my numbers and can’t seem to find the two line items that I need to change the algorithm anywhere? Right now I was able to just goto the bodycm and change the diameter based off the above tire calculator and that took me from being 4-5 mph slower to 4-5mph faster. Can someone please point me to the right direction to update the algorithm 726-xxx or what is the proper way to do incremental changes so I can get my system dialed in properly. Any help would be great. Thanks

I have a 2021 F150 Lariat Powerboost as well that I just put new ridge grappler 295/65r20's on. Base setting was 2547 and I changed it to 2800 and the same thing happened as you were describing. Plan to try 2750 next and see where I land. let me know if you figured this out or not. Thanks.

trevtitan45 wrote: Tue Nov 09, 2021 12:15 pm

alzev wrote: Fri Jul 09, 2021 12:36 am I have followed this and every other link related to properly updating my tire size. I have 2021 f150 lariat power post and can’t seem to get it dialed in. I downloaded the spreadsheet that someone had spent a lot of time making and plugged in my numbers and can’t seem to find the two line items that I need to change the algorithm anywhere? Right now I was able to just goto the bodycm and change the diameter based off the above tire calculator and that took me from being 4-5 mph slower to 4-5mph faster. Can someone please point me to the right direction to update the algorithm 726-xxx or what is the proper way to do incremental changes so I can get my system dialed in properly. Any help would be great. Thanks

I have a 2021 F150 Lariat Powerboost as well that I just put new ridge grappler 295/65r20's on. Base setting was 2547 and I changed it to 2800 and the same thing happened as you were describing. Plan to try 2750 next and see where I land. let me know if you figured this out or not. Thanks.

Just an FYI, followed instructions from spreadsheet w/ tire calculator and got speedo corrected.
https://docs.google.com/spreadsheets/d/ ... 2133040050

that is good but can you post a short video about it too?!