Just installed a set of 275/70-18 MTR Kevlar's on my 08 auto unlimited sahara stock rims with OME HD 2" lift. Also have weight of ARB bumpers, 9.5 ti w/ synthetic and a pair of IPF 968's. Also am running AEM intake and Borla cat-back. I stand to be corrected, but thought the 3.8 computer adjusted to your style of driving,(and mine is somewhat brisk ). However, after installing the 275/70/18 MTR's, I have noticed a definite increase of back and forth with the overdrive at 70 mph. I have approx 750 miles on the new tires and do not seem to notice any computer adjustments to the new size. My questiion is can I effect the adjustment with something like a pro cal recalibration of tire size? Or are new gears the only remedy? thanks

 

It can not "sense" tire size changes. You have to buy a programmer of some sort to recalibrate tire size. Wheel speed sensors are used for to calibrate speed not the tranny so gears shouldn't effect speedo. If your talking about power decrease after larger tires, you've just increased the amount of weight and decreased to gearing to drive it. You're jeep will have a noticable drop in power. IF you think it's bad now, try 35's. With that said your Auto also has more driveline loss then a standard so it will be more exaggerated then my jeep.

 

thanks for the reply. That is what I was suspecting. I have been thinking of a pro cal to make some adjustments to see if that will correct it and I guess I should try that before any further modifications. I have noticed that if I turn off the overdrive, it does fine but I am noticing a loss in mpg's and would prefer to keep my overdrive.

 

like thousands of other members on here. I installed 35's on my JK and had power loss..

What I have been doing to remedy it is drive wit O/D off. the MPG loss really has not been horrible, but I want more power...
gears are pretty much out of my price range and lately there have been a few members grenading their Transfer Cases (gears can be part of the cause) which would make me think twice even if I had the $.

Anyways, I already have the procal to correct the speedo, which it does well.

I just ordered the SuperChips Jeep Flashpaq hoping it also helps. If it were a perfect product, I will be able to install the 87 or even 93 tune and be able to run with O/D on.. we shall see what happens when it arrives. I ordered it a week ago today and haven't received anything yet

 

Your solution my friend is the Superchips Flashpaq from Dave at Northridge. Let me give you my reasoning.

The ProCal is a pretty straight forward tool. It's like a screw driver. It does one thing really well, change variables for tires and tire preasure.

The Flashpaq is a tool box. It has a ton of adjustments you can make that will allow you to take advantage of that intake and exhaust your running in addition to changing tire size and tire preasure for the TPMS. The performance tunes actually do year positive results and I love mine. It's also USB upgradable so it's never obsolete. Superchips has been great about releasing updates.


Regearing is great on paper but it's a drastic solution to your problem. Depending on which model year you have you may have the Lifetime Powertrain Warrenty. Changing gearing will definatly void that. Also, you're looking at a couple thousand just to get back to stock performance. I'd regear only as a last resort. Give the Flashpaq a try first.

 

thanks for the advice. Read WOL's and JPOP's writeups on the flashpaq and can see where it will probably fill the bill. Jeep runs fine with od off, but I feel like I'm thowing away an extra gear and would prefer to have it back. Never have been too keen on gears for fear of a sloppy install along with possible dealer issues. Honestly, I am glad I did not get 35's, the MTR Kevlar 33's do look good on the Jeep and I have had several remarks from people who notice such things. So flashpaq it is. Will try to report on findings after installation and testing.
(this sure is a good place to lgain iniformation on your JK)

 

From everything that I have read here on this website is going to 33's the flashpaq will be all that you need. It will adjust your shift points in your trans and give you that more like stock feel. I have really been debating 33's or 35's for my jeep and 33's are sounding better everyday with all of the failures that are occuring. But then again a ton more of people arent having problems, so I guess its a case of buyer be ware.

 

I think that's a case of volume. X-Boxes were famous for failing but I don't know one person personally who's had one fail on them. 35" tires are the most common size ran after a lift kit so it makes sense that there would be proprotionally more trouble reported with them.