baddceo

I highly recommend anyone who hasn't changed the rolling diameter of their wheels to get FORScan or have someone who has the software to reprogram your ECU. I am in a 2018 Limited, upgraded the wheels and tires to 33x12.5x20 from my OEM 275x45x22. I wasn't an initial believer that such a small change 3-4% would change the driving behavior of the truck. Over the weekend I ordered my dongle from Amazon and got my FORScan software setup. I am an experienced software person but doing things like this to the ECU on a truck still made me nervous. I followed @Livnitup's directions and everything worked exactly as it should. I was able to reprogram the circumference and I am about .5 MPH off on first try which I am not sure I am going to be able to correct. I took my 33x12.5x20 and converted it MM which is 318x52x20 and that gave me a code of 09F4. Now instead of being 2-3 MPH faster I am nearly dead on. The more important note here is how such a little change impacted the shift points the rougher feel of the drive and the MPG average which I don't hold a ton of faith in. I also tweaked my home screen to include heated seats and steering. It's odd how such little things don't make it to the production runs like that. I will also add the auto window up/down feature so on those hot days I can get the windows down 100 feet before i get into the car. Nice feature that I have always programmed into my German cars. No idea ford had that.

Thanks to those on this forum that spend countless hours putting tutorials together so people like me can make these changes themselves without fear of blowing something up. It's selfless support and I for one really do appreciate it. All in this effort cost me $29.99 worth every penny and now I have the software to make changes as I see fit.

Livnitup

What is the model name of your Toyo tires? I've added your value to my user-submitted tire size values here: https://docs.google.com/spreadsheets...#gid=110328400

baddceo

They are Open Country A/T II 33x12.5.x20 I am going to stick a level and ruler on them this evening to see if inflated circumference is a little taller. I suspect that is the case and while a half a mile per hour isn't the end of the world i'd like to see how much more spot on I can get. There are many moving values here as the entire height is a variable of width and sidewall. I don't think ford Hexadecimal cares about anything other than that absolute circumference. I'll respond back if there are notable changes to the actual tire height.

jp360cj

FWIW, this seems to hit or miss on actually changing the speedometer, especially on the pre 2015 trucks. Maybe the newer trucks are more consistent. Also, it's interesting that you noticed a change in the driving behavoir. Forscan can't actually change anything in the PCM (powertrain control module) which controls the engine & trans.

jp360cj

Is your speedometer reading too fast or too slow? Too fast indicates you need a value for a shorter tire. Too slow indicates you need a value for taller tire. Toyo specs that tire at 32.5" tall.

baddceo

What I noticed initially before the change was hesitation in the shift points. Maybe it is psychological but it feels smoother.

baddceo

It's reading about .5 MPH too slow now. Where I am 50 or just a hair over my GPS speed indicates 49.

Livnitup

The PCM relearn service procedure in FORScan for 2015-present trucks does adjust tire size in the PCM (it tells the PCM to use the current tire size values in the BCM) so it is conceivable that shift points would change slightly. 2018+ trucks also run the TCM relearn procedure when setting tire size that does the same to the Transmission Control Module

baddceo

This would explain it. As well just the read out on my average mpg history has changed quite a bit. I am running actually fuel mileage through Fuelly so I can tell how much it is off. Just started that so I don't have any numbers from it yet. What I can see is that I am still showing 17.1 as my average 90% in city. Still think that is going to get lower but the history prior to the change was probably showing around 16.5 and now it's consistently at or above 17 and change.

whoopidoo

I overlooked this at one point, and I'm not clear from the thread if you used this specifically, but this link below I found in the forscan spreadsheet. Note the fine tuning options (in tenths of a MPH) halfway down this page:
https://docs.google.com/spreadsheets...EqU/edit#gid=0