35's is a different story. OD would be useless because there wouldn't be significant RPM's to provide the power. I understand your point about the bicycle gears, but you have to state both sides of the story. Pedaling on level ground in the lowest gear will take a significant amount MORE energy at anything but very slow speeds because you are having to pump those pedals super super fast. There's no way you can talk me into believing that 2500 RPM's puts less stress on a JK than 2000 RPM's at 65 MPH. This would even be more true at lower speeds. The higher RPM's are not NEEDED, although they definitely enhance performance (and engine wear, although it is still a minimal amount).

Edit: I'm only referring to a 2012 Auto.

 

now im a bit confused
i understnd that higher rpm's are more strain on the engine

lets say arguments sake...i put the 33's on
obviously there is the loss of power from the 29's to the 33's based on wheel size/weight

the 3.21's wil lturn the wheels but i would assume, my rpm's wil lbe higher to turn those wheels i nlower speeds, therefore i want to get back what was lost and possibly have a little more "umph"

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if i go - regear to something in the 4.range (4.1something)
are my rpm's running higher or lower in the lower tranny gears? (local streets)
are my rpm's running higher or lower in the higher tranny gears? (highway)
-keep in mind, im auto-

from what i thought...going to the new gear ratio, ill be running higher rpm's
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i also thought that a regear dosnt "add" more HP/torque, it just allows the vehicle to get to its better power ranges more efficiantly - which in turn equals higher rpm's?

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so, if that is correct, that the new gears run at higher rpm's - how does a tuner not kind of take the place o the regear?
if in fact a tuner does allow the vehicle to pump out more HP/torque, doesnt the more output allow the wheels to roll easier? granted, again, there is strain on the engine since it is working harder

 

Talk to jpop on here dude...he's pretty good with this.....and in my opinion it will put more stress on your drive train because how the transfer of torque will be....Idk just how I look at it....because just like with anything the lower it is geared the more force and torque u will have on certain components of your drivetrain,yes it may take you back to stock like performance, but gotta remember when you were stock you had like 29 inch tires and then moving up to like 35 or 37s adds alot more to the whole variable.... which is no different than anything else that uses different gear ratios....and a tuner isn't putting more strain really....all internals are the same, the engines brain is slightly modified and dosent do anything that could harm it unless u abuse it ofcourse...may not know alot about re-gear...but I've had like a billion tuners in the past few years lol tried a few on my f150...im.not a expert by no means just throwing my 2 cents in .....but talk to jpop dude for sure

 

or is it spelled jpopp lol I cant remember lol

 

I know that my '08 has no problems with 3.21s with my stick shift. I added a tuner and it runs better than stock. I don't feel the engine straining as much.

However, being as you have a 2012 - there is no tuner available.
Having an auto is a lot worse than the stick shift, and I would recommend a re-gear. Do it right the first time and you can run 35s with no problem.

 

You will lose some UMPH for sure.

Compared to 3.21's and stock tires, with 3.21's and 33's , at a given speed, your RPM's will be slightly lower. This, and the added weight of tires, is where you lose some umph.

With tire size being the same, 4.11 axle gears will have to turn MORE rpm's to go the same speed as 3.21 axle gears. You will have more "get up and go" with the 4.11's. This is the same whether you are on highway or city driving. 4.11's is a damn good performance gear match for 33" tires. You won't be squalling tires with the 3.21's.

Sort of - the higher RPM's causes the better power range. Think of HP as a product of RPM & torque. 5252 is the number we use to figure it out on paper. If you get 200 ft lbs of torque at 3000 RPM's, then you do (200x3000)/5252 = 114 horsepower.


Jeep owners often say that extra HP(tuners, exhaust, CAI) is a bandaid for improper gearing. SUV/Truck drivers that are riding behind big V8's that have plenty of horsepower will tell you that gears are a bandaid for lack of power. They are both true, because of the way RPM's and Torque interact. With an engine of lesser power, you need higher RPM's to have usable HP. This is why gearing is NOT as big of a necessity on 2012 models. There is more torque from the engine, and more HP due to the much smarter Automatic transmission gearing.


From my own research on this forum (and what I know from other vehicles I've owned), this is what some of the veterans have advised me to do: get the tires you want, drive with it, and see what you think. Get a tuner (sucks for 2011 & 2012 models, we don't have one), and see if that makes up the difference. If you still need more power, plan to regear. The labor that goes into regearing both axles is enough to justify going ahead with aftermarket lockers or LSD's front & rear as well - that way you can do it all at once. Most folks say its between $1000 and $1800 for gears and labor, and a big chunk of that is labor. I got quoted a little lower than that in my area.

If you're going to spend all the money on regearing, you should probably bump up to 35's. 4.56 or 4.11 gears would be a good match for 35's. 3.21's...not so much, but I think you could deal with the 33's just fine.

 

Regear. No question.

 

Think about it this way.

Your drivetrain basically uses leverage to turn the tires. Sorta like you lifting a certain weight at the end of a teeter totter by pushing down on the other end. Factory setup ideally would be the best combination of distance, height, and length of the lever and position of the load for you to easily push down on it and move the load all day long with minimal fatigue.

Changing the tire size would be like putting a larger weight on the end.
Now it's harder for you to move it.

Now, you may be strong enough that you can just push a tiny bit harder and up it goes. May never notice it. May notice it only after a good long time of doing it. It is however harder.

Putting larger, heavier tires on and not regearing would be akin to putting a larger load on the end and expecting you to still be able to move it with the same setup as the original. You may be able to do it but it will be further from ideal the heavier the weight gets and you'll notice it more and more.

Regearing would be akin to moving the balance point and/or changing the position of the pivot and the load on the other end. You end up restoring the setup to some configuration that results in you putting as close to the original effort as possible.



A tuner or headers or supercharger or exhaust or whatever other performance mod would be akin to you pushing down harder on the lever in order to make up for the lost leverage over the heavier weight. It works but again, you're working harder.


Now, let's complicate it further.
In the real world we're also dealing with tires of varying heights and weights, your intended use, your "seat of the pants" butt dyno and personal tolerance, how big of a change from stock you are making, and the way your particular drivetrain makes and puts power to the ground.
I know turbo diesel truck guys making huge honking numbers that have 35's or bigger with 3.55 gears. They have so much torque that they honestly don't notice the difference. Is it there? Yes. It just doesn't matter much when you're making 400ft/lbs of torque at idle.
As said above you may want to slap the tires on and see how you like it. Grab the ProCal, recalibrate your computer for the tires so your auto trans shifts correctly (this is important!), and drive it. If you don't mind, it don't matter. If you do...how bad is it? Seem just a little bit slower? Maybe you can slap a K&N in the filter housing and a freer flowing muffler in place of the factory constricted junk. I've personally done something similar with minor tire changes and had it work out well enough that I never took the time to do more.
If you find it noticeably slower off the line and don't like it then it may be time to start saving for a gear change.

Gear change = restoring the system to the stock "leverage". You're reconfiguring the teeter totter and load setup so that you have to put about the same effort into pushing down on your end.
Performance mods = adding more power to hopefully make up for the additional power your now "out of balance" system needs to move the vehicle. You're putting more effort into pushing down on your end of the teeter totter but maybe you've done some 'roids and bulked up and don't notice as much. Still, leverage wise, the system isn't in balance as it was originally.

Again, YMMV and opinions differ and what some people can live with for thousands of miles or tens of thousands of miles others hate on the first drive.

 

Great Speech!! Helps put it all in perspective and also makes the answer easy....re gearing is the only true solution. The other options mask a problem rather than address it.

 

Thanks. Can you tell I've explained it a few times?

People tend to put it off into magical land and not entirely understand it. "I should do this because others say it's what you do when you do x." However if you put it in simpler, easier to understand terms most folks will get it and understand.

Best case is regear AND do the performance upgrades later to get better performance.