Speedometer Indicates 10% High But Odometer is Correct?

[thundercles]

Hello, I am the proud owner of a new 2022 2500 Cummins Laramie. I've noticed that the truck speedometer indicates ~10% higher than actual speed. I have checked speed with multiple GPS apps and roadside radar and the truck consistently shows 10% faster. I understand that most vehicles error on the low side and might indicate ~1% higher than actual but 10% is excessive. Although the speedometer shows 10% high, the odometer seems to be showing the correct value. Are the speed and the distance calculated independently? I understand I can change the tire size via Alfa OBD, dealership, or other programmer but I don't want to change the tire size to get correct speed and then see that my odometer is reading 10% higher than actual. Thanks in advance for any insight!!

PS: I've searched the forums but everything I've seen just mentions the speedometer recalibration for different size tires.

 

[MtnRider]

What did the dealer say about it?

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[LateToTheParty]

Both are related to revolutions per mile, so when you calibrate for one you are calibrating the other.

But since you've posted in other threads that you went to a taller tire, you should actually be reading the other way around (speedometer/odometer both reporting lower than actual) unless you've already reprogramed for the new size.

 

[thundercles]

Agreed. The issue was there before I went to a slightly taller tire. The slightly taller tire actually helped get the actual speed closer to indicated. I spoke to the dealership that sold me the truck and they said I would have to leave the truck with them for "a couple" days for them to investigate. I was hoping someone here had some insight in the meantime.

 

[Jimmy07]

Make sure that when you use gps apps to check the actual speed, your phone is completely divorced from the Uconnect radio (Bluetooth and CarPlay/Android auto disconnected).

 

[MtnRider]

But since you've posted in other threads that you went to a taller tire,

^ That would have been useful information he Should have posted here. "I went to a taller tire and now my speedometer is off"


/

 

[thundercles]

Jimmy07 Nailed It! Thank You! Turned the phone bluetooth off and the GPS and truck speedometer matched (minus the small differential from the 1" taller tires)! I had not even considered that the multiple GPS apps I was using were wrong. Very strange that the GPS speed was constantly 10% slower than actual. Lesson learned. I guess this is a known issue with the phones and Uconnect5 system. Thanks Again!

Thanks MtnRider for the less than helpful replies. I didn't mention the 1" taller tires because they weren't relevant to the issue I was experiencing. Let me know if you need a full explanation why...