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Discussion Starter #1
Recently my front left speed sensor failed, and my speedo was off 3 MPH. The dealer replaced the speed sensor (and wheel bearing for a noise I was hearing that didn't solve the problem).

Is there any way to adjust the speedometer so it matches GPS speed? It was perfect before this happened, now it's driving me nuts!

I was curious if the AlphaOBD app might have an option to adjust the offset. The dealer says its within spec and won't change it.

Thanks!
 

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FYI.....GPS speed is not always accurate.... A speedometer is not always accurate either.

Just because your speedometer doesn't match your GPS speed, does not necessarily mean your speedometer is incorrect. We don't calibrate speedometers based on GPS. It's done by tire size. As tires wear, the accuracy of the speedometer changes because the diameter of the tire changes.
 

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Discussion Starter #5
The Ram forum has people change the tire size so that the speedo is correct all the time using alfaOBD.
https://www.ramforum.com/threads/alfaobd.123982/

FYI, it's alfaOBD not alphaOBD. It's alfa for Alfa Romeo.

Cool. I ran though the app and found the setting. It's in a sub-menu, but it's there.

i read through a post from the link that you sent, and it looks like I need to study up on this app and how to initialize the ABS system before I begin.

Have you found a good tutorial that would get me started using the alFaOBD app? (I work for Chrysler, I should have known better than to misspell it)

FYI: I went from matching GPS to 3 MPH difference in a day. I don't think tire wear is a factor. I understand your comments though about wear and GPS. Thanks
 

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Well, Here is how I fixed the problem.
https://tiresize.com/calculator/
When I replaced my tires I went to 245/45r17 from 225/45/r17. Now my analog Speedo, my digital speedo and my GPS are all the same. And I needed that.
 

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3mph in one day = weather change most likely. Your profile says Ohio, did you just get a blast of hot weather like we are in Michigan? That's gonna increase your tire pressure and change the diameter of the tire which changes the speedo accuracy.
 

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by very minimal amount though...and though the life of the tire. i say negligible.
I didn't say it was a lot....lol

I've never had a car where GPS speed and the speedometer have matched.
My nav GPS and speedometer are the same, only diffrence is the GPS speed is 1mph slower than my speed-o- for like a second when accelerating.
 

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GPS units simply blows turkey dung since they depend on an outside source to make them work .

Get on a road with mileposts an when you pass a milepost, look at where your tenths numbers are at. When you meet the next milepost, the tenths number should be exactly a mile more.

Are you running recommended size tires, or went awol in customed sized tires WHICH will eff up the mph off either slow or fast.
 
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