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Discussion Starter · #1 ·
I have a 2012 Jeep Wrangler Unlimited Rubicon. Previous owner had it lifted at 4 wheel parts in Indiana.. Its running 305 70 r 18 tires.. Never payed much attention to the speed o till a couple of days ago.. I was in a work zone of 45 and passed one of the speed machines.. It said 54. Now is the machine off or is my truck. Questions How can I check if the speedo is re calibrated?? The good thing I guess is I'm putting less miles per speed on my jeep...What would I need to check or calibrate the speeedo
Thanks
Jim
And I cant figure out how to rotate the picture...sorry
 

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Discussion Starter · #2 ·
One more thing... I have noticed I do not have the option to check tire pressure on my dash... was that not an option on the 2012's??
 

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You can download a GPS app for you phone that will work as a speedometer. If it is off you can have the dealer correct it or buy a procal unit and do it your self. Mine was off 10% due to the wrong tire sizing.
 

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Discussion Starter · #4 ·
I'll have to get an app.. If I remember right the speed on the nav was the same as the dash guage.. Either it gets its info from the truck or the speed trap was off.. I'll compare the app the truck and drive by the machine next time I get a chance
 

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This is pretty common with lifted Jeeps (not because of lift). The speedo works with three main factors: Tire size, Diff gear size, and the "speedo gear" as I'll call it. If you wanted to get the car on the exact speed you'll have to have those three things placed. Which is pretty pricey.


A couple cheapish alternate fixes are as stated above by bpaintx, you can get an app on a smartphone to tell you or you can get just about any Garmin GPS and they'll have it too. Another option is to go to your 4x4 store and get a programmer Super Chip is the best for your money in my opinion.

The programmer will get you pretty close to the real speed is you have the true dimensions of the tires (simply take a tape measure and check). But again you won't be dead on. The only real way to be 100% sure is to have it re-geared at a dealer.
 

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Do you have a tuner (device)?

Best (cheapest still?) option here might be an AEV ProCal unless you need a superset of its functionality. Get to the bottom of the boot loader issues before buying SuperChips.

With the ProCal, you can set the PCM to have the correct tire diameter if you re on other than stock size.
 

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I have a 2012 & 2005 nether have a gear to correct the Speed, its electronic.

You need a programmer.

When you use a programmer be sure to put a level on top of your tire and measure from the bottom of level to ground, that is your tire diameter.

Do not use the size on the tire or the tire manuf. size. With the right input u will be right on.

With the right programmer u should be able adjust the tire pres. on your 2012
 

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I have a 2012 & 2005 nether have a gear to correct the Speed, its electronic.

You need a programmer.

When you use a programmer be sure to put a level on top of your tire and measure from the bottom of level to ground, that is your tire diameter.

Do not use the size on the tire or the tire manuf. size. With the right input u will be right on.

With the right programmer u should be able adjust the tire pres. on your 2012
This. When you set the correct tire size like was mentioned here with a programmer, that will also correct your shift points if you have an auto trans. Everything is electronic and tied in; speedo, tire size, auto trans. and if it was re-geared from stock. That can also be done with a programmer if it applies.
 
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