On a 2 door 07 JK. How big of a tire can you go to before the 3.8 V6 and 4 speed auto are not going to have the ompfh to effectivly spin the tires?[HR][/HR]

 

I'm going to assume 2500lbs of tire as it can tow that much. How big are you planning on going? Some are running 42s on this site, I'm running 37s and don't find it that bad, but then it all depends on your gearing as well. If you could give a little more info as to what your planning then more people can help you out. There are some pretty knowledgeable jeepers on here.

 

Depends 100% on the gearing.

 

i have 315/75R16s with 5.13 gears and its peppy as hell. Moving to 37s eventually. I think there are a few here with 40s too.

 

Stock size...

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The question is even with proper gearing, is there a point you reach with tire size that the stock V6 engine really doesent make the power needed. Implying a hemi swap is the next step?

 

If you go bigger than 37's, it's probably time to start thinking about an engine swap. Remember, as the tires get larger, they also start to get heavier!

 

This is dumb. Not trying to flame you but it's silly. The 2 door can tow 2000lbs and 4 door 3500lbs... Why do you think? Because the 4 door has a different 3.8L? The towing has to do with wheel base. It's also while you're only supposed to have 100lbs of tongue weight. Now 3500lbs might be nearing what Jeep believes the engine is capable of towing safely but if you throw 3500lbs on the 2 door and jump on the brakes at 60 mph you've got a pretty good chance of doing a wheelie and that would be youtube worthy... I believe there is a guy on here with the four door and a special hitch towing a 5500lbs trailer. I'm not saying it'd be fun but it works. Gears are your friend.

 

I had a 4.10 gear setup in mine from the factory. 2007 JK X. I had some rubi take offs on it which seemed fine. Once I went up to 35s and steel wheels it was a dog, always downshifting. Sometimes never even getting into OD. I went with 5.38s and I could not be happier. I am not really concerned to much about mileage. It does seem to have gotten better though.
Crawling rocks or anything with this setup is 100% better. I have only wheeled the new gears once but I am so much happier with the regearing. A few of us are heading out wheeling for new years. Cant wait!

 

With the right gearing, any tire size that fits is possible. When the gearing is right, the engine turns about the same speed as stock and the power to ground does not change.

You would need to worry about axle and gear strength before you run out of engine power. That's because the bigger tire weighs more and the weight is further from the center of the wheel. This calls for a stronger axle; the 3.8 is plenty stong enough to bust up a stock diff trying to turn 40" tires against rocks.

If the 37" or 40" tires add as much weight as, say, 3 adults, then put 3 big passengers in the Jeep and go for a drive. You'll get an idea how much difference the weight of big tires will make to the Jeep's engine performance.