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Old 03-22-2014, 09:35 PM   #1
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Actual Speed with 33 Tires

I am wondering what is my actual speed according to my speedometer (dont want to get caught speeding on the highway!) with 33x12.50-15 LT tires with 3" suspension lift?- 2004 TJ.

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Old 03-22-2014, 09:36 PM   #2
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I have same size wheels and tire and lift on my 97 tj and I think it's around 5mph

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Old 03-22-2014, 09:39 PM   #3
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At higher speeds it's worse. Mine is about 5 mph at 70 with 32". At 35 it's a couple off.
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Old 03-22-2014, 09:40 PM   #4
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It won't be a fixed mph, it will be a percentage, so the faster you go the more it will be off.
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Old 03-22-2014, 10:59 PM   #5
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I have a similar setup, and mine is off by a little more than 10%. I used a speedo app on my phone to check mine. In other words, if my speedo is at 20, real speed is 22-23 mph. If my speedo is at 50, real speed is 55-56 mph.
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Old 03-22-2014, 11:04 PM   #6
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Do you have a gps or smartphone? Download a speedometer app....

I have 31's and at 65mph im doing 69. Less the slower I go, but I just keep it at 5 under to be safe.
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Old 03-22-2014, 11:04 PM   #7
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Quote:
Originally Posted by Water Dog View Post
It won't be a fixed mph, it will be a percentage, so the faster you go the more it will be off.
+1 - exactly

I use a free app on my phone to check my speedo.
I have a couple vehicles that are off on the speedometer.

The app is called "GPS Speedo"
Works great and it is FREE.


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Old 03-23-2014, 02:03 AM   #8
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Quote:
Originally Posted by Water Dog View Post
It won't be a fixed mph, it will be a percentage, so the faster you go the more it will be off.
Why is that? The gear having more or less teeth doesn't change it into a linear scale
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Old 03-23-2014, 03:21 AM   #9
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Yes it is linear.
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Old 03-23-2014, 09:17 AM   #10
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Yes it is lnear and is a fixed ratio based on tire circumference which is also proportional to tire diameter

So for example it was reading correct with 30 inch tire and you put on 33 would now read 10% low which is zero error at 0 speed 3 mph error at 30 mph and 7 mph at 70mph
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Old 03-23-2014, 11:18 AM   #11
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Just correct your speedometer with the correct gear or if it is an electronic type sensor with one of the boxes like this which is what I use on my Rubicon:

Official home page of the Yellow Box Speedo Recalibrator

Even more needed if you are driving an automatic to get the shift points right.

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Old 03-23-2014, 11:30 AM   #12
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Old 03-23-2014, 11:54 AM   #13
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If you have a smartphone download an app called WAZE it will tell you what speed your going.
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Old 03-23-2014, 03:27 PM   #14
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Just get the correct speedo gear. They're cheap and it only takes two screws to replace.
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Old 03-23-2014, 04:08 PM   #15
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If you have a wrangler TJ not a "Rubicon" you dont have electric box. Only Rubicon has that. If you have factory dana 35 with 3.07 gear and runing 31' tire you need new 27tooth gears. Its like $35 takes 10 minute to change ib the transfercase.
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Old 03-23-2014, 04:11 PM   #16
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Forgot you have 33' you need 26 tooth spedo gear with 3.07 for factory calibration.
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Old 03-23-2014, 04:13 PM   #17
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Just depends which way you count the change ie two numbers 10 and 11
11 is 10% more then a 10 baseline but 10 is only about 9 % lower then an 11 baseline so the numbers 10 and 11 are both 10% and 9% apart depending on which way you go 10 to 11 or 11 to 10
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Old 03-24-2014, 01:23 AM   #18
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My rubicon has 33s and my speedo was dead on. GPS confirmed. No speedo recalibration necessary.

Flash
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Old 03-24-2014, 07:24 AM   #19
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Maybe someone else recalibrated it before you got it. My wife's 04 rubi runs correct with 33 also and I just think the prior owner had it recalibrated After the larger tires were installed
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Old 03-24-2014, 08:44 AM   #20
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From what I have gathered, Rubicon speedos are actually factory calibrated for a 33" tire despite being sold with a shorter tire. Mine is just about perfect with 285/75r16 which measures 32.5".
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Old 03-24-2014, 11:26 AM   #21
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From 2003 FSM

"˛ Electronic Pinion Factor - The EMIC stores
the tire size, axle ratio, and transfer case type information
for use in calibrating the proper vehicle speed
and distance values for display by the speedometer
and odometer, as well as for use by other electronic
modules in the vehicle. The EMIC provides this
information when requested by other modules over
the PCI data bus. Changing the electronic pinion factor
settings of the EMIC requires the use of a
DRBIIIt scan tool. Refer to the appropriate diagnostic
information."

so on the rubicon just a quick trip to dealer plus some fee and should be corrected
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Old 03-24-2014, 12:44 PM   #22
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Got money? here's an idea.
Get a SS SYE/DR Shaft and a blue monkey speedo healer.
Turns your non Rubi into an electronic speedo.

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