Tuning after a gear swap? Is it Necessary? 2015 Ford F-150 5.0


Active member
I never went into forscan and changed the settings When I swapped to 4.1 gears and raptor takeoff wheels any tires on my truck.

I know me speedometer is off but what else is affected by not setting the gear ratio and tire size.

truck seems to work better with the overall lower ratio.


Active member
oem It was 3.55 the factory tires were 275 70 18

now it is 4.11 with 315 70 17.

is it better to adjust with forscan or just get a tuner?

if a tuner which one?


Well-known member
Would probably be fine just using Forscan.
I used an SCT X4 tuner.
When I put the factory tune back on the truck drove like garbage, off shifting, speedometer out, plus the factory throttle lag was back.

Deleted member 9101

With Foracan you can change it in 3 min for under 50.00.

Now, if you are getting a tune anyways, it's redundant.

Once the truck knows what gears and tire size it has, it will preform much better. I went from 3.15 to 3.55 gears and 32" to 33" tires and even correcting for those small changes made a noticable difference.


Active member
Ok so I changed the gear ratio in the BCM.
is there anywhere else I need to change?
do I need to tell the pcm to relearn or something?
it threw a code that said the pcm and bcm do not match.

I also have not changed the tire size yet.

What spreadsheet did you use to to get the tire size value?

I found two different spreadsheets with different values for the same tire size.


Active member
So I put in the new tire circumference and told pcm to relearn.
Speedometer went from reading low to reading high.
Still getting a code
Did I miss a step?