I read through the Forscan threads, I don't see where anyone posted a confirmed tire size change. Has this been done by anyone? I would like to change my size to the 275/65/20 preset.

 

pretty sure the dealer can do that for you. That is a stock tire size and the Ford computers have that program in them from the factory.

 

You can find it in the thread below that blkout50 has been working on.

https://www.ford-trucks.com/forums/1...lt-data-6.html

Page 6, post 77

I can't say it's been confirmed, but he's done a lot of great work finding these options.

 

That's cool, so I can see the code to change in Forscan. I really want to hear from someone who has been able to make the change on a 2017 though. I think I will PM him. Thanks.

 

Our sheet is for11-16. I have not seen a 17 sheet started yet. The values may be more similar to the 15-16 F150.
Go to the first page of the post. I reference a great post from member livinitup from F150Forum. Tons of info been a great help.
Keith

 

I have changed it on my 17 and the speedo reads correctly for my 40's but it does throw a dtc. The 150's in the forscan forums were doing the same thing. Whats more annoying? The dtc or speedo off?

 

Hey thanks. So you changed it with FORScan? Did it throw the dtc because it is not a preset tire size like the 275/65/20? TIA

 

Yes changed it with the FORScan. Looks like it throws a tcm code for being to far out of spec. If you change to biggest offered from factory you might be ok.

 

any possible way we might be able to fool the sensor with a resistor or potentiometer?

 

OK, dredging up an old thread here but it's the most closely related to what I want to do.
Thought maybe to bring it back to life would save some clutter on the general FORScan thread.
Check out the link in post #3. Has anyone done this for tire size change? I currently have 275/65R18 tires that are 32.1 inches high. I'd like to go to a 34 inch tire to fill the wheel well a little better as well as have a more aggressive tread than the Continentals that are on the truck.
The table listed below shows a value for 275/65R20, which is exactly 2 inches higher (34.1) than my stock tires. If I could find a 295/70R18 it's 34.3 inches, probably close enough for speedometer accuracy.
A couple of other 18 tire sizes measure out to 34.6 and 34.8. I could even do that if the BCM had the values somewhere in it for FORScan to change.
Any information on this is appreciated. As soon as I know for sure what I can do without setting a malfunction light, I'll get some tires ordered.
Here's the graphic link from thread cited in post #3 of this topic:

Attachment 196067

 

I would start by selecting the largest "stock" tire size available. Then cross check accuracy with a GPS. On your reference chart look at the last line in the tire size area, you see the ABCD. To the right is a link to a custom size page calculation. You can go any size you want for total accuracy. Keep in mind that if you get outside the variance parameters you will most likely set a P160A code. ForScan only writes to the BCM here. There is a reference in the PCM that we don't have access to yet. As I recall.
Let us know if this helps.
Keith

 

The ABCD link appears to only lead to a page with the same chart. I don't find any additional info on tire size values.
But if those codes shown hold true, I could go with a 295/75R18 at 34.3 inches and use the code for 275/65R20 (34.1 inches), which would put it within 2/10 of an inch.
Also, the FORScan speadsheet we're all using shows that a person bought 285/75R18 (34.8 inches) and used a code for that size that appears to work for him. But he was only bumping up from a 275/70R18 (33.2 inches).
So he went up 1.6 inches. If I were to go to that same 285/75R18 I would be moving up 2.7 inches. I'm wondering if the larger difference would affect accuracy or cause the P160A?
I want to get some tires, but I want speedo accuracy. These figures are making my head hurt!

 

Hey guys. I went from factory 18” continental contitrac to factory 20” wheels and factory size option with KO2 275/65/20. Tires were mounted at the dealership and I walked the tech thru IDS to changed the size. After a few days I felt I was going faster than others at posted speed. I doubled check with 2 phone apps simultaneously. Sure enough it’s off. 5-6%. Don’t know if it was accurate prior to making the switch. Trying to get my hands on a gps to be more accurate. Oil change coming up within 2-3 weeks so I will be discussing with the tech again. Was the 1st one to make a tire change so they won’t have much history there. I did receive my ordered OBDII dongle for forscan. That will be the next step... just a little scared to get into this haven’t had time yet to understand the proper steps. But there is a few items I’d like to knock off that forscan list once once I’m comfortable !!

 

OK try this link.
https://goo.gl/kKm5uw

This link is from the 11-16 SD ForScan Sheet.
I have confirmed it works.

 

I've only had FORScan plugged in and made some changes one time, I'm new to it like you. My advice is to check out the tutorials at the bottom of the spreadsheet here:
https://docs.google.com/spreadsheets...s1s/edit#gid=0

Also, ask questions here of the experienced people. Everyone so far has been willing to help out a rookie like me.

Edit: OK, I originally didn't see that I could actually punch numbers into the spreadsheet in your link to calculate the hex values. This makes life simpler!
I also stumbled upon a link for F150s where the PCM could relearn after BCM reconfiguration with FORScan to remove the MIL. Of course now I can't revisit it! Nor do I know if would work on 2017 F250s.
My hat is off to those who have done all of the experimenting and provided all of the information that we currently have.