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Tire size increased but speedometer still appears accurate

NJMonark

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Has anyone changed their tire from the stock 285/45R22 to 33x12.5R22 and noticed it didn't require a speedometer recalibration? I recently did this and while there was a clear size difference between the OEM GY Eagle Touring tires and my new 33's, a speedometer check using "Speed Meter" up to 70mph shows it's spot on. Unfortunately I didn't measure the old tire height before getting them swapped so I could compare (new size measures 32 10/16"). But I'm guessing it was off to begin with and now it matches. (FWIW, not connected with Android Auto and Bluetooth disabled).
 

BowersFJ

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Guessing your factory size was 32ish ? A move to 33” isn’t gonna yield a huge difference …. Not one you would notice any way …. On my 2012 I went from 33’s to 35’s and found it to be 3-4 mph off …. By the way, your math teacher would be very disappointed that you didn’t reduce 10/16 to 5/8 …. Lol …. Sorry, couldn’t resist


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ferraiolo1

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My 33s didn’t change the speedo at all from the stock Laramie tires.


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BowersFJ

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My 33s didn’t change the speedo at all from the stock Laramie tires.


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Speedo won’t change …. It’ll just be off a lil


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ferraiolo1

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Meaning it didn’t change via gps

When I’m doing an indicated 55 and my phone says 55 ( not connected to the truck) with the stock tires and my 33s


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BowersFJ

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Meaning it didn’t change via gps

When I’m doing an indicated 55 and my phone says 55 ( not connected to the truck) with the stock tires and my 33s


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Validates my point that 1” dia change isn’t worth recalibration


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djevox

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Has anyone changed their tire from the stock 285/45R22 to 33x12.5R22 and noticed it didn't require a speedometer recalibration? I recently did this and while there was a clear size difference between the OEM GY Eagle Touring tires and my new 33's, a speedometer check using "Speed Meter" up to 70mph shows it's spot on. Unfortunately I didn't measure the old tire height before getting them swapped so I could compare (new size measures 32 10/16"). But I'm guessing it was off to begin with and now it matches. (FWIW, not connected with Android Auto and Bluetooth disabled).
You sure you had thephone unplugged from the truck? I just had this same scenario yesterday. It was the same in Waze as the truck said, but when I unplugged the lightning charger cable, the speed was off by almost 3 miles an hour at 70 mph.
 

Idahoktm

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Your speedometer won't be spot on with 33's, but it won't be off by more than a few mph. That said, I recalibrated mine after I installed the new tires.

Tire difference.JPG
 

NJMonark

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@djevox
No I didn't have it connected and didn't use Waze. I downloaded another GPS app. And I disabled Bluetooth just to be sure although I don't think it was necessary.

@Idahoktm

This is what I expected to see; a 2.4mph difference @ 70 but it matches 70. I do have a Hypertech 752504 but don't know if it's worth going through the exercise to change it since I'm not seeing
a difference.

Good catch BowersFJ!
 

ALT_F13

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Went from 33 to 35, and for some reason 80 mph speed still shows as 80 mph on the dash. Don't understand how it worked, maybe truck calibrated the speedometer using GPS data from time to time. But I will be checking what tire size is set up in the settings, since I need to modify tire pressure settings via AlfaOBD anyway.
 

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