This is about highway driving at 60 MPH -

With 32" KMs and 3.73 gears, the JK shifts out of overdrive AND unlocks the torque converter (TC) when the Jeep sees the slightest hill. The RPM jumps from 1650 to around 2900. The TC pretty rarely locks up in 3rd gear. If it did lock up, the RPM would be around 2400.

If I change to 4.56 gears and 33s, the 60 MPH RPM in OD will be about 2000.

Questions:

With 4.56 and 33s will the gearbox stay in overdrive more often for mild hills?

With 4.56 and 33s, when the box does shift out of OD, will the TC stay locked (~2900 RPM) or will it unlock (~3450 RPM).?

I like the idea of 4.56 gears, but don't really want to run 3500-4000 RPM every time the Jeep sees a small hill on the highway.

Thanks in advance.

 

Not really an answer, but the auto trans is supposed to drop down a gear when it hits a hill. Every vehicle typically drops a gear when hitting an incline to put the motor in the proper RPM range (powerband) therefore you don't have any drive-ability problems. You shouldn't be in OD trying to go up hills anyways, based on the intended use of OD. It's the same as everybody complaining about having to drop a gear in a standard when they hit a hill, they obviously don't understand the concept of the powerband for an engine or realize you should be in the powerband before you hit the hill and should understand what that is. Auto's are slightly different in that most people don't pay attention to it lol But they should figure it out to optimize their driving experience and save the engine all the wear and tear.

You can re-gear to whatever you want, but your finally ratio in OD will increase therefore raising your cruising RPM so on flat long distance drives you'll lose MPG. If that's a concern for you and you do a fair amount of highway travel.

As far as how the vehicle reacts to the hills will vary on the hill, slight inclines and your tranny should stay locked at a certain RPM, but if you get a steep hill or hit the gas while going up, it could drop down 2 gears to say third or second and yes your RPMs will jump up to say 3500 or whatever it may be for that ratio vs being locked at 3000RPMs.

I'd say just take it out of OD whenever you hit a long hill if you see the RPMs beneath 2400, because you already know that's not in the optimum powerband/RPM range for the engine to efficiently move the vehicle forward. I find with 35s and a 6spd our powerband starts at 2600RPM, anything below that and the engine may start to lug if we go up a hill. Since I know this I make sure I'm at least around 2800-3000RPM as I enter a steep hill if I want to increase my speed up the hill or maintain it.

If you already know all this, sorry for the explanation but it seems most people here aren't really thinking about driving the vehicle as opposed to just letting the vehicle drive them if you get what I mean

 

Did you check the chart in Modified Tech FAQ? Was curious why you're considering 4.56, when the chart recommends 4.88 or 5.13 with 33's. My jk-a dogs along with the same rpm's. Noticed you have Trac-Loc. Is that Rubicon locker, Chrysler LSD, or aftermarket? You like it? I'm considering a trutrac LSD.

 

Thanks for the replies

@otservice - I understand your post, and I'm not one to let the rig drive me. Its not my intention to defeat the shift pattern, just want to get some feedback on how the shift pattern changes when the final drive ratio changes. The drive train will think hills are not as steep with lower (numerically higher) gears - but will it make a lot of difference or not much at all?

@Sargejk - The nature of my question is the answer to yours. I don't want to run the bag off my engine getting down the highway for the sake of a bit more throttle response, but I also hate the way the engine likes to lug for the sake of economy, and the way it shifts on the same slight upgrades that my other rides can handle. Looking for the sweet spot in the middle. The gear chart is a nice piece of work, and really useful, but its set up with maximum performance as the only consideration.

 

I have a similar 2010 JK. I wanted to regear to 4.56 to get a bit more performance, but also have to tow heavy things with overdrive off for hours on end. I realized that if I regeared to 4.56, the rpms with OD off would be over 3000, so I didn't do it. I did find that the tow tune in superchips helped a lot with the performance, though. It may not be available yet for the 2011s.

 

Saturday morning bump. Must be somebody out there running this combination?