When we went from the 0952 to 099D, that was 75mm more of tire circumference. For another 75mm increase in tire circumference can go to 09E4 (actually only 71mm) and will max out on the accepted range the PCM will take (at least for a '11-14). Any higher and another gear ratio tweak will be needed. For 75mm increase and a gear ratio tweak, use this as your line 726-12-01: 0163 0962 xxxx

 

Thanks to your efforts, your work for my truck's puzzle, I factored your claim of 30mm additional circumference being worth 1 MPH (within the range of the gearing hexadecimal you're using).

To gain 1.5 MPH, I added 30mm and 15mm to get 45mm additional circumference. This would be 2506mm or 09CA hex.

Seems to work for now but as noted it will be a few weeks before I may accumulate +/- 300 - 400 miles' short hops before I might sustain 70 MPH vehicle speed to measure this latest tire circ hexidecimal. Right now we're bang on the money for 50-55 MPH, my present break-in speed limit.



I could not! have arrived at this present conclusion without you.

I still have no idea what math you used to fudge the axle ratio to where the faux tire circ starts working. I am at a loss there. Again, thank you and I shall update this at the next opportunity!

 

Do you think that 30mm is universal or only applicable to your setup? I'm currently seeing 1mph faster on the speedo compared to Waze GPS.

 

30mm is an estimate for about 1 mph change. So if your speedo is reading high, you could reduce the tire circumference 30-40mm and it should get you closer.

 

Thanks @KRUISR !

I took my AsBuilt circumference of 2462 (099E) and multiplied by the change in circumference for my new tires and got pretty close on the speedo.

 

Anyone remember what the factory number in forscan was for 275/60-20 tire. I'd per the factory number and not calculator for my OCD. lol
2631mm ?
Thanks.

 

That's not a factory Ford tire size. 275/55/20 was. That circumference is larger than the range the PCM will accept.

 

False.
I bought it new with 8 miles from Ford Dealer. lol. Mine is a 2022.
Appology accepted.

 

Well, then download your AS BUILT data from Ford and get your answer.

 

Then why have a forum like this.
Dont be hurt because I proved you wrong.
Its a simple question. Ill wait for an answer.