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Old 09-04-2011, 12:18 AM   #1
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REprogramming Jeep for the correct Tire size Question!!

My JK came equipt with the scrawny 16" steele wheels with 225/75/16 tires.

I added Wheels and 265/70/17 Toyo MT's. The speedometer and Odometer are off now. Speed is off by 5 mph(reading 55 doing 60 on gps) and the Odometer is off by 10%.. (odometer reads .9 miles but actual distance is 1.0 mile)

The dealer says they should be able to program for the correct tire size (32") or get really close..

So my question is... If they reprogram, would it do anything else to the shifting points or other performance characteristics, or is it just going to fix the Speedo/Odometers?? Its a 5 speed Auto-- if that matters.

Other than accuracy on speed and distance is there any benefit by getting it done?? I kind of like the idea of saving a few miles and leaving it as is.

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Old 09-04-2011, 03:33 AM   #2
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I dont believe the dealer can do it (or at least most wont).

The procal has been the godsend for the up to 2011 models, but I believe they will have a 2012 version out by the end of September. This will reprogram the speedo/odometer and also change the shift points to match the net effective taller final gearing achieved from the larger tyres.

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Old 09-04-2011, 06:00 AM   #3
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Just remember when they reprogram or if you have to get Procal when the update comes, you will not put in the actual tire size which for a 265/70/17 is 31.61", you will need to compensate for compression on the road. The computer will more then likely need to be set at around 30.50 to 30.75". Common is around 1" less then actual tire size. The computer goes in .25 increments.

May have to go either side of this but this would be my best guess to start with. That assumes you use proper air pressure. Example is my tire which is a 285/70/17 which is 32.71. My computer is set at 31.75 to get the speedo correct. But when I went to change mine from the stock tire size of 255/75/17 the size in the computer was 30.75 and a 255/75/17 is 32.06"

The dealer should be able to reprogram since you are not running over 32" tires. Once you go over that most dealers claim they can't change it. I have a hard time believing that but that what many report they tell them.
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