Forscan to set tire size, size out of range?

[EJH]

I tried to follow this thread to adjust my Ranger's tire size after installing 31.5" tires (265/65R18), which are +1" over the stock size.
https://forscan.org/forum/viewtopic.php?t=15994

265/65R18 (31.5") tires have a circumference of 2517mm.

When I went to change this is BdyCM, the preset value was 23xx (I can't exactly remember, but it was lower than even the OEM tire size).
My truck will not allow a value large enough. Anything close to 2400mm or larger will throw the "tire size value out of range for this module" error.

How are others setting the tire size?

I'm sure it can be done, and it should be valid as my new tires are the stock Tremor size.
But what is odd is the preset value isn't even the stock (265/60R18) value, which is 2433.

Thanks,
Ed

EDIT: I drove at 50mph with the cruise set, and my phone's GPS says I am going 50mph.
That is odd. My truck has GPS Nav. Does Ford somehow do a calibration with GPS every so often. My speedometer is dead on based on GPS speed. Even if it was set to the OEM size, I should be off by about 2 mph at 50 mph, and way more than that based on what it set for tire circumference in the BdyCM.

BTW, Discount Tire did not re-calibrate the tire size, see below.

Somehow the truck must have recalbrated iteself?
Or it was set to a higher tire size from the factory? I never tested the speedo w/ GPS before

My guess is the truck was set at th factory about 4% higher than stock size, which is a about the difference +1" in tire diameter makes. From my Googling, speedos seem to be set higher from the factory, doe liability reasons. I'll confirm when I put my smaller snow tires in in November and go a GPS speed test.

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[MountainGoat]

Yeah it's 3.2% lower in general. Mine is set to 2439 for 265/70/R17s. That would put yours at 2436. So it's pretty much on. I didn't get any error messages setting that.

 

[EJH]

Yeah it's 3.2% lower in general. Mine is set to 2439 for 265/70/R17s. That would put yours at 2436. So it's pretty much on. I didn't get any error messages setting that.

That matches what I finally found on the Forscan forum. 0.967 times the actual value.

Thanks for confirming.

 

[Grandaccess]

I have 285/70/17 I figure I am off by about 10% when the dash says 60 my GPS says 66, maybe one of these days I will buy a cable and forscan and play with it, but since I know what it is, it dont bother me

 

[RangerPNW]

I tried to follow this thread to adjust my Ranger's tire size after installing 31.5" tires (265/65R18), which are +1" over the stock size.
https://forscan.org/forum/viewtopic.php?t=15994

265/65R18 (31.5") tires have a circumference of 2517mm.

When I went to change this is BdyCM, the preset value was 23xx (I can't exactly remember, but it was lower than even the OEM tire size).
My truck will not allow a value large enough. Anything close to 2400mm or larger will throw the "tire size value out of range for this module" error.

How are others setting the tire size?

I'm sure it can be done, and it should be valid as my new tires are the stock Tremor size.
But what is odd is the preset value isn't even the stock (265/60R18) value, which is 2433.

Thanks,
Ed

EDIT: I drove at 50mph with the cruise set, and my phone's GPS says I am going 50mph.
That is odd. My truck has GPS Nav. Does Ford somehow do a calibration with GPS every so often. My speedometer is dead on based on GPS speed. Even if it was set to the OEM size, I should be off by about 2 mph at 50 mph, and way more than that based on what it set for tire circumference in the BdyCM.

BTW, Discount Tire did not re-calibrate the tire size, see below.

Somehow the truck must have recalbrated iteself?
Or it was set to a higher tire size from the factory? I never tested the speedo w/ GPS before

My guess is the truck was set at th factory about 4% higher than stock size, which is a about the difference +1" in tire diameter makes. From my Googling, speedos seem to be set higher from the factory, doe liability reasons. I'll confirm when I put my smaller snow tires in in November and go a GPS speed test.

Thats interesting that you got an error when you tried to go to the larger size in Forscan, I've linked my post below about how I got my speedo accurate, and the initial number input into forscan was over the 2500 like you tried and no errors were presented. Mind you i still had to drop it down a bit.

https://www.ranger5g.com/forum/thre...can-speedometer-calibration.13651/post-282988

 

[EJH]

Thats interesting that you got an error when you tried to go to the larger size in Forscan, I've linked my post below about how I got my speedo accurate, and the initial number input into forscan was over the 2500 like you tried and no errors were presented. Mind you i still had to drop it down a bit.

https://www.ranger5g.com/forum/thre...can-speedometer-calibration.13651/post-282988

I didn't dial down exactly what value causes the out of ranger error, but it is somewhere between the 2380 I was able to set and 2400 (which threw the error).

You ratio method in your post to calculate the circumference matches what is on the Forscan forum: use 0.967 times the actual circumference.

I'll need to drive more with a GPS but my quick drive at 50mph yesterday had things pretty accurate. I think the value I set (2380) is close to a 31" diameter tire. I still don't understand why I cannot go more than 2400mm without the PCM error? Ideally, I should be about 2430-2440 for a 31.5" tire.

That all said, if I am within 1-2 mph at highway speeds, I am happy. I use winter tires for 5 months of the year that are OEM size (30.5") and these new A/Ts for 7 months of the year at 31.5". Having the truck set at the average of those two is fine. It keeps me from changing Forscan back and forth each time I swap wheels. I figure I can be 1-2mph low on my A/Ts and 1-2mph high on my winters.

 

[got3fords]

I realize a small MPH error is tolerable, but that could throw off the long-term actual miles on the odometer.

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