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Old 04-03-2014, 05:21 PM   #1
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Rubicon Speedometer

I know the difference in the standard TJ with its speedo gear and my '03 that has the speed sensor. I had set my mind on the Dakota Digital unit that I have read about on here.

But I am confused!!

I just finished my Zone 4.25 and a fresh set of 285/75r16's installed. ( roughly a 33x11.5). I took it to get aligned today and while at the shop I downloaded a speedometer app for my phone. On the way home I could only find a 1
Mph difference and that was at 55 and above! Below that speed it was practically dead on.

Shouldn't there be more of a difference? I know the size upgrade isn't that big since the Rubicon comes with a 31" from the factory but I still expected enough of a discrepancy to warrant a correction. Don't get me wrong, I'm glad if I don't have to spend that money, but do you think it seems right? Could the app be off? It uses GPS tech. So I would think its accurate.

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Old 04-03-2014, 06:34 PM   #2
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Could get a more sensitive gps or get a tag along vehicle you trust and compare but many 33 tires are 32.5 or less and true rolling diameter is trice distance ground to wheel center so any low pressure compression of tire counts double

Bottom line if reading is adequate as it is well if it ain't broke

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Old 04-04-2014, 04:35 AM   #3
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The 2003 and 2004 Rubicon EMICs (Electro-Mechanical Instrument Cluster) are actually calibrated for 33" diameter tires. Early Chrysler Rubicon test mules actually used this tire size. A very late decision not to release 3" lift coils on the Rubicon model was made after the EMIC was in production. The speedometer's actually would not be calibrated for the stock 31" tires until the EMIC was re-programmed in 2005 and 2006 for the 6-speed manual transmission.

So YES I believe you. I'm guessing you have a 2003 or 2004 model Rubicon.
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Old 04-04-2014, 01:37 PM   #4
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Thanks a lot, that is great info!

So I'm wondering if everyone running around on factory 31's are getting incorrect speeds?
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Old 04-04-2014, 02:13 PM   #5
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So your are saying Chrysler got away with having 03 04 rubi SPEEDO AND ODOMETER READ 2/33 or about 6.7 % higher then actual. Since 04 had a 7 year 70 K warranty they cheated it down to 65K real miles when odometer read 70K? Sounds highly suspect.
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Old 04-04-2014, 02:15 PM   #6
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I had the same thing with my 03, and I would guess they did read a little bit slow from the factory
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Old 04-09-2014, 04:36 PM   #7
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YES, that's what I am saying. The EMIC and the other digital "smart parts" have to be submitted for approval long before the rest of the Jeep. Anything that effects the smog or mileage readings (for the new car window sticker) that the Federal DOT must test is on the long approval cycle. Springs and other suspension parts are on the short approval cycle that the manufacturer self-certifies.

My speedometer did not read correctly until I got my 33's. The error was not large enough to require correction in Chrysler's opinion.

The 31's that the Rubicon shipped with as Plan B were still the largest factory tires ever put on a Wrangler as of 2003, and would remain so until the JK Rubicon got 32's. I just wish the factory had fitted the 3" coils and the 33's on the 2003-2006 TJ Rubicons. But the lawyers shied away from that.

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