Speedo Recalibration FYI... - Ford Powerstroke Diesel Forum
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Old 04-24-2012, 10:25 AM
hua hua is offline
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Speedo Recalibration FYI...

My rig info:
2012 F350 Lariat, Build date 1/12...

For those that are looking to go with larger tires and want to have the speedo recalibrated, this is what I learned. I upgraded the size of my tires to 325/60 R20 and went to the dealer to have the speedo reclibrated. When they gave me back the truck they told me they set it to that specific size. I thought I would double check and do a GPS comparison. It was still about 3 - 4 MPH off. I called them back and they said it will take a 20 mintue trip for it to recalibrate. (Weird but thought whatever.) Many trips later still off by 3 - 4 MPH. I found a local garage (to have them change the TPMS setting, another story) and took it down there. I had him verify the tire size in the computer and this is what it showed. The max tire size available to choose is 275/65 R20 and that is what it was set to. That is why I'm still off 3-4. Attached is the photo of the parameters allowed. So I guess the only way to go bigger is with a tuner.
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Speedo Recalibration FYI...-20120424_101455.jpg  
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Old 04-24-2012, 01:15 PM
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I remember when dodge did mine they went into the abs computer and adjusted the revolutions per mile and that corrected my speedo. Weird thing is that my tranny shifted better and the brakes responded better as well. Was kinda surprised about that.
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Old 04-24-2012, 02:18 PM
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You are correct.........thats one reason why I went no bigger then 295/70/18. When I get the computer updated to 275/65/20, then (according to my math) I should only be .3 mph off.
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Old 04-25-2012, 03:09 AM
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Agreed, they can only upgrade to a stock tire size. In addition, that tire size must be available from the factory with your specific axle ratio. You won't be able to get a 275/65R20 with a 3.31 axle because that combo doesn't ship from the factory. I'm sure there are others that have had similiar issues. Glad I'm like bltp and had 3.55's.
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Old 04-25-2012, 11:18 AM
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I had my dealer do mine. I went to a 325/65/20. All the bigger my dealer could go is the factory size 20's. I have 3.31 gears so it wouldn't let him program to the 20" tires. We ended up reprograming it to 3.55 gears & the 275/65/20 tires. I only off about 1 mph now.

Just an FYI of how I did mine.
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