Setting arbitrary tire sizes for speedometer calibration

[ralwood]

I am posting this here for those of you struggling with the same situation that I am facing on 2013 F150. Yes, this is the procedure I have been using. After considerable trial and error, I have learned that when the PCM relearn throws an error it is also not writing this information to the PCM and therefore no changes are taking place in the speedometer. It seems that on the 2013 F150 this is limited to something in the neighborhood of 2650MM tire as it takes the change for 265/60R18 from the table. This is certainly better than the 2356mm that was originally programed in when I bought the truck, but is still leaving me with about an 8% error at the speedometer (down from about 13%). The PCM relearn will simply not take the 2774MM for the tires that are on the truck whether I use the simple method or go in and change the value in the "as built" tables. Always throws back an error and does not make any change to the actual performance. I thought I might try to change the axle ratio in the BCM and let it "fool" the PCM into the right overall result. No such luck there either as my truck is equipped with 315 gear and apparently this is also limited by the PCM relearn, not allowing values outside predetermined limits. As of now I'm better off than I was with an 8% error down from an initial 13% error in speed. Better but not where I want to be. If anyone has any insight or suggestions on fine tuning this further, I would like to hear from you.

[RyanMF]

I have the same issue with my 2012 F150. From everything I have read, there is some kind of issue with 2011-2014 that the tire size cannot be changed. I have tried everything from changing the As Built in the BCM to the preloaded BCM settings from Ford. Nothing changes. My speedo is also about 8% off and probably for ever will be. I have only come across one person that says they got it to work, but nobody else.

I will echo what you have said - if anyone has any suggestions or thoughts on how this can be rectified, please post.

R

[ralwood]

Thanks,

I really don't want to go buy a tuner or some other device to correct this if it can be avoided. I'm not interested in more HP etc. I just want accurate mileage, trip calculations, oil change intervals etc.

[Wiley16]

I'm new to all this so read this with a grain of salt. When I look at the tire size parameters in the PCM using HPTuners, the default is set to "learn from BCM", which is what we're discussing here: set the tire size correctly in the BCM. But the PCM offers the ability to calibrate the tire size in the PCM, if you turn off "learn from BCM". I'm not suggesting anyone switch to HPTuners. But when you're calibrating tire size in the PCM, you have opportunity to calibrate not just current tire circle, but minimum and maximum tire circle(s). I don't know why the PCM needs min/max values. When I read about changing tire size in the BCM using FORScan, I haven't seen anything about changing min/max, just changing currently installed tire size. So either the BCM won't store and convey min/max and the only option is direct programming of the PCM (perhaps with FORScan) or, if the BCM does store min/max those locations have to be found and adjusted as well.

[crewdog89]

I have a 2013 F-150 XLT supercrew 4x4 w/off-road package and I bought it new from the dealer who had a 6" pro-comp lift and 35x12.5R18 Nitto tires installed. The dealership provided me with a hypertech speedo calibrator with the purchase. However, the speedo was always 5mph faster than actual speeds. The hypertech tune just wasn't accurate. When I first discovered FORSCAN and came across the various threads for changing the tire size in order to calibrate the speedo I tried just about everything I read that may apply to my situation. Nothing worked. Finally I gave up entering all the different hex codes generated from the excel spreadsheet floating around. Granted, I have a 2013 and I believe the spreadsheet was created specifically for 2015 & newer so that could have been my problem all along. Anyway, I ended up using the largest tire size available in FORSCAN (I can't remember the exact size but it started with 317) and also changed my axle ratio to lowest available which was 4.10 and BOOM!, my speedo was dead accurate. My factory axle ratio setting was 3.55, does anyone foresee any issues down the road with what I did? I really haven't noticed any difference in gas mileage or how the truck drives. I appreciate anyone's input.

I know this thread is still somewhat old but is there an issue with changing the axle ratio? I have a 2014 xlt 3.5l ecoboost my speedometer reads 60 but gps has me at 64.5. I went through the spreadsheet and adjusted both As Built and Non As Built parameters and neither process worked. I read that the Max circumference is around 2650 and my tire size x squish factor (.967) comes out to 2629 and when I tried that it didn’t change anything and I was still within the max circumference parameters

I decided to return back to stock clear the DTC’s and try again and still no luck. I read the axle ratio comment and want to know if something like that can cause damage or any other issues. I just want to have an accurate speedometer haha

Tire size is 275/65R20 (34.1” tire)

[RyanMF]

There appears to be no solution for this gen of F150’s. I tried everything you mentioned as well (circumference, tire size, axles ratio, as built, etc.) None of those worked for me either on my 2012 Screw Eco boost. The only solution I have seen work is by using an after market tuner or calibrator. I purchased a FlashPaq turner and had to install an eco tune to get my tire size corrected. Good news - Speedo fixed! Bad news - developed a mis fire after installing the tune. Removed the tune and misfire disappeared. I was about to purchase this unit (you can google it - Hypertech 3300 Speedometer Calibrator with Color Screen) to make the adjustments, however, popped one of my tires and unfortunately, couldn’t source a replacement in my area. So went, back to stock. Hope that helps.

[crewdog89]

That does help a lot. I was searching forums and videos and articles and came up with nothing but this Gen period is SOL haha. Calibrator it is I guess hopefully mine doesnt throw codes like yours did but we shall see!

[RyanMF]

You will be fine with that calibrator as it ONLY adjust the tire size. The tuner I had would only let me up change the tire size if I uploaded the tune. That’s where the problem lied for me. Good luck!

[isdeekelis]

Hi,

I have 2015 c-max energi. Have tried multiple times to change tire size, but i always get 10% higher reading in speedometer. Have tried entering tire size -10% and +10% from actual size, but same speedo inaccuracy. Maybe someone has ideas how to make speedo to be spot on?

[rbentnail]

Hi,

I have 2015 c-max energi. Have tried multiple times to change tire size, but i always get 10% higher reading in speedometer. Have tried entering tire size -10% and +10% from actual size, but same speedo inaccuracy. Maybe someone has ideas how to make speedo to be spot on?

After you make the tire size change, go back to the configuration and programming tab and reset the PCM and any other modules you have a reset option for. On my 2013 F150, changing tires size alone does nothing to correct the speedo readout. Resetting my PCM and clearing any DTC completes the process.