Speedometer Calibration For Tire Size

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Nov 17, 2016 | 12:04 AM

TexasGuy001

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Speedometer Calibration For Tire Size

I recalibrated the PSOM for 31 10.50 15 tires using the code 9.14. Since doing that, the speedometer reads nearly 5 mph higher than it should at 70 mph. I'm wondering if I should reprogram it for a 30 9.50 15 tire using code 9.52 or try something in between those two. I have recalibrated the PSOM for this tire size before with the same setup on my last truck and the speedometer was accurate within 1-2 mph at 70.

Nov 17, 2016 | 12:25 AM

The_Drew

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I would suggest actually measuring the tire before recalibrating. Actual tire sizes vary between manufacturers even within the same "measurements"

Nov 17, 2016 | 04:21 PM

jas88

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I always use percentage to tell me how much. You need to reduce speed by 7%. How much was it off before you did the calibration?

Nov 18, 2016 | 12:36 AM

TexasGuy001

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It seemed to read about 5 mph low, but I never checked it with GPS before recalibrating it.

Nov 18, 2016 | 09:21 AM

jas88

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I've forgotten now, it's been so long, but aren't you only allowed a certain number of times you can reset the tire rotation value?

Nov 18, 2016 | 03:49 PM

rla2005

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Quote:

Originally Posted by jas88

I've forgotten now, it's been so long, but aren't you only allowed a certain number of times you can reset the tire rotation value?

I believe that number is 6

Nov 18, 2016 | 03:53 PM

TexasGuy001

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Yeah, it is limited to 6 so there are 5 remaining. I have no idea why Ford designed it that way.

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Nov 18, 2016 | 05:40 PM

Eddiec1564

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From: Arcadia, Fla

Quote:

Originally Posted by TexasGuy001

Yeah, it is limited to 6 so there are 5 remaining. I have no idea why Ford designed it that way.

To keep odometer fraud from occurring is main reason.

There is a way to reset that back to 6 just need to be able to copy and write the EEPROM of the PSOM.......and no anything over 6 will crash it....