37z and speedometer

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beachbunny1959
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Joined: Tue Jun 23, 2020 2:15 pm
Model Year: 2018

37z and speedometer

Post by beachbunny1959 » Tue Aug 11, 2020 8:46 pm

how far off is the speedo wearing 37z?
tia

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ScubaSteve
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Re: 37z and speedometer

Post by ScubaSteve » Wed Aug 12, 2020 9:51 am

I don't remember exactly, but its enough that its worth having it recalibrated. Not difficult at all if you get an OBDlink and AlfaOBD. No idea what the dealership would charge.

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Bill2014
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Re: 37z and speedometer

Post by Bill2014 » Mon Aug 17, 2020 11:30 am

Tire circumference is Pi times diameter.
Stock tires are approximately 33" in diameter and you are running 37's
So your actual speed will be 37/33 what is reading on the speedometer.
If you don't make a correction, when your speedometer reads 60mph you will actually be going 60x37/33 = 67.3mph

But you need to get your computer set for 37" tires to correct your shifting points...
2014 Power Wagon Laramie
Titan V5 2.5" Receiver Pintle Hook
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TroyH
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Joined: Mon Dec 28, 2020 3:54 pm
Model Year: 2016

Re: 37z and speedometer

Post by TroyH » Thu Dec 31, 2020 8:24 am

Mine is about 7 MPH off, you really notice it on the down shift, or the 2 to 3 shift under minimal load. I will be getting a programmer soon. Just have not decided which one.

iowa
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Re: 37z and speedometer

Post by iowa » Thu Jan 21, 2021 3:00 pm

I just got the new and improved AEV Procal Snap. So far it’s working great.
2020 RAM Power Wagon
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