WARNING - Dealer reprogramming larger tire size (2012+)
04-26-2013, 01:46 AM
#21
JK Enthusiast
Join Date: Jul 2009
Location: Peoria, IL
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I'm not sure about the drive train issues, but if it's an automatic then it will run like crap if you don't get a PROCAL or something like it. Your difference in fuel economy alone could buy 4 PROCALS at 15000 miles per year not to mention the irritation of poor performance due to the transmission not knowing the actual shift points because its perceived RPM difference due to a 1" different tire diameter. I've tried this cheap approach and it doesn't work on an automatic...if you have a stick shift then don't worry about it, your speedo will be the only thing that's off.
04-26-2013, 02:08 AM
#22
JK Super Freak
The wallaceracing dot com site says the 285 is a 32.71 versus 31.06 for the 255. That is about 5.4 percent difference so your speedo at 70 is off by 3.78 mph approx. That site even has a calculator that will compute the difference for you on the speedo but I didn't use it, only the tire size one for this. Very handy site for doing gears and tires.
Go 'Noles !!
04-26-2013, 02:18 AM
#23
JK Super Freak
I'm no expert. So this could be all BS. But an auto that doesn't shift at the proper torque could cause problems with the torque converter and gears. And if one of those systems should fail for any reason, your warranty claim would surely be denied because of improper set-up. Some mods simply require other "supporting" mods to go with them. I really don't think your drivetrain will break tomorrow. But that doesn't make it any less important.
Usually you want to modify the shift points for power and efficiency so the engine isn't lugging while keeping rpm high enough to be above stall so you don't needlessly heat up fluid and waste fuel with unneeded slip after putting on larger tires. This also keeps you in the power band as you drive when shifting is done by the control module and not the driver.
Go 'Noles !!
04-26-2013, 02:32 AM
#24
JK Super Freak
I'm not sure about the drive train issues, but if it's an automatic then it will run like crap if you don't get a PROCAL or something like it. Your difference in fuel economy alone could buy 4 PROCALS at 15000 miles per year not to mention the irritation of poor performance due to the transmission not knowing the actual shift points because its perceived RPM difference due to a 1" different tire diameter. I've tried this cheap approach and it doesn't work on an automatic...if you have a stick shift then don't worry about it, your speedo will be the only thing that's off.
Go 'Noles !!
04-26-2013, 09:48 AM
#25
JK Enthusiast
Thread Starter
Mileage was aprox 18.5 MPG on the highway before the tires, and has gone to aprox 16.8 MPG - however I still need to do a lot more driving to confirm/validate that (and that's using the dummy gauge - converted to MPG).