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-   -   Speedo calibration? (http://www.jeepgarage.org/f109/speedo-calibration-63361.html)

jerkylips 07-27-2013 12:27 AM

Speedo calibration?
 
So I've been helping my dad through the buying process.. he's anxiously awaiting delivery on his Limited. I talked with the dealer about a tire swap. They're happy to do it but commented about "calibration issues".

The tires I'd like to swap to are the Cooper Discoverer AT3's (which I run on my Liberty - AWESOME tires) but they don't offer the OEM size. The OEM is 265/50/20 and the Coopers are 275/55/20. The dealer made a comment about maybe being able to have the speedo recalibrated but wasn't sure.

According to the tire calculators I looked at, with the speedo reading 65 actual speed would be 68. I'm not sure it's that big of a deal but does anyone know if the speedo on the '14 can be recalibrated for different tire sizes?

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brando26 07-27-2013 02:34 PM

Dealer should be able to change tire size with their drbiii scan and program tool.

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Raptor 07-27-2013 03:56 PM

Re: Speedo calibration?
 
No your dealer will not be able to calibrate your speedometer to work with a non OEM tire size w/a scan tool!

An aftermarket tuner should be able to do this while changing the fuel and ignition curves for better performance w/ different fuel grades...... but no one has been able to make this work without disabling the ABS system. :mad:

See the many aftermarket Diablo tuner threads for more info.

AZhiCntry 07-27-2013 04:11 PM

Re: Speedo calibration?
 
Quote:

Originally Posted by jerkylips (Post 865371)

According to the tire calculators I looked at, with the speedo reading 65 actual speed would be 68. I'm not sure it's that big of a deal but does anyone know if the speedo on the '14 can be recalibrated for different tire sizes?

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That's only about a 1% difference. Not enough to bother with. I wouldn't even worry about it. Most stock speedos are not even that accurate to begin with.

jeffreybehr 07-27-2013 04:35 PM

Re: Speedo calibration?
 
Jerkylips: "...with the speedo reading 65 actual speed would be 68."

Quote:

Originally Posted by AZhiCntry (Post 865598)
That's only about a 1% difference.

...ahem...let's see... 3/65ths = 0.046 = 4.6%. That's a bit more than 1%... :)

...and maybe enough to get you a ticket if the indicated speed would have already been pushing a particular patrolman's 'allowance'.

tomk 07-27-2013 04:41 PM

Re: Speedo calibration?
 
the AT3 doesn't have much available in 20" ..

He just needs to remember his speedo reads low and leave it at that.

Without a tuner the tire diameter options are very limited; the factory calibrations are for the OEM tires only.

jerkylips 07-27-2013 06:08 PM

I think I misspoke in my first post. When going 65, the speedo would read 68.

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jeffreybehr 07-27-2013 06:50 PM

Re: Speedo calibration?
 
Quote:

Originally Posted by jerkylips (Post 865653)
I think I misspoke in my first post. When going 65, the speedo would read 68.

You were correct the 1st time. When one installs larger-diameter tires, the car now travels faster than it did at the same speedo setting.

My new 275/55-20s are about 32" diameter; the originals were c. 30-1/2" 265/60-18s. I checked my speedo against a GPS receiver that indicates speed to 1/10 of a MPH, at about 2-dozen speeds from 40- thru 70MPH. Then averaged the 2 columns to determine that my speedo is now 3% slow...and that's OK--I just need to be more aware. :o

Tony407 10-22-2013 06:28 PM

Re: Speedo calibration?
 
I visited my local dealership today for some unrelated issues and asked them about this. The adviser (not a tech) told me that have a few tire sizes they can choose from when recalibrating the speedometer, but wasn't sure what those tire sizes were. I couldn't get him to commit to a more definitive answer. I'm in the same boat, wanting to upsize to a 32" diameter tire.

Tony

ColdCase 10-23-2013 03:04 PM

Re: Speedo calibration?
 
Tire sizes provided in the scan tool selection menu are OEM only, and since all WK2s have the same diameter tires (regardless of wheel size), there really is nothing available to pick that will correct the indicated speed.

Other Chrysler products have a variety of OEM tire sizes so there is a number of options to select from the menu, but typically here folks are going way bigger anyway. Without looking, most techs and service writers assume the WK2 tire factor is adjustable, just like the wrangler.

Some dealers will put into the system that you are running oversize tires which can be a problem for some warranty claims down the road. I've read of at least two WK2 transfer case problems denied for oversized tires.... although there may be more to the story.


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