i have a '12, auto w/3.21
once i have some $ - im looking to get rims/tires
i would like to go to 33's - no plans on going bigger than that
my jeep is a DD, mostly local streets and the once a week 1/2 hour highway ride, and the once a month fire road treck

i know there is no flashpaq or programmers for the 12's - yet...
and the fact that a re-gear is $$$$$$

so, my question...
for arguments sake, lets say there was a programmer for the 12's

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-what would be the pros / cons of either a re-gear or a programmer (aside from the expense)?

-whats putting more strain on the engine on local streets and highway usage - the 3.21's, or 4.1's? i would assume the 4.1's since ill be running higher rpm's OR is it the other way around?

-what would put more strain on the engine - the regear or the tuner?

 

Regearing to a lower (higher numerically) ratio puts LESS strain on the drivetrain and engine assuming you regear to the optimal gear ratio. If you went 5.38's and 33's then yes you'd be wringing the life out of the engine just to get up to around town speeds. Fast off the line though...

The easier it is for the engine to spin up and the less the transmission has to hunt for gears the better it is. Regearing would return your system to optimal condition and result in it driving better.

Example - once had a '96 Ford Ranger 4x4 4.0L V6 and 5 speed stick. Came from the factory with 3.27 gears and 29" tires. When I bought it 31's were on it and I was lucky to see 12mpg. Very slow off the line and OD was hard to use except at freeway speeds (60+).
I regeared to 4.56's and put narrow 33" Swamper radials and despite the heavier, taller tire I immediately was getting a solid 14-15mpg. Owned it 3 more years and got that consistently the whole time.
The engine had to work less to move the vehicle and was in a better rpm range the whole time so I saw better performance and mpg as a result.
YMMV.

To me, unless you're just slightly bumping up the tire size, doing performance mods to counteract the bigger tires is a bandaid. 20 more hp won't make up for the fact that you're vehicle is now high geared and wheezing off the line and dropping out of OD at 55mph.

 

Ok, you asked which would have MORE strain on the engine - and the answer to that would be a tuner. Now, just so you'll know, the higher (lower #) gears wil put LESS strain on the engine that lower (higher #) gears. This is why a JK with 3.21 gears gets better MPG than one with 4.11's.

 

You're being kinda broad there dill.

If you're too high geared you're working the engine hard to start moving and will have trouble maintaining OD gear except at very high speed.

There's a reason a lot of folks on here say get 3.73's no matter what on your stocker. Many seem to report even with stock tires the 3.21's are too high.

 

Actually a 3.21 gear will put more load on the engine than the 4.11's if running larger tires

 

OP said 33's. The height difference there is going to be pretty negligible. The only time there will be more load on the engine will be at highway speeds. He's only one the highway for 1/2 hour a week, and he has a 2012 with the AUTO transmission. He's going to running about 2000 RPM's at 70mph with 3.21's, and 2500 RPM's with 4.11. The performance might be better with the 4.11's, but thats not what the OP asked.

 

Just to validate, I have a 2012, and mine is a standard transmission. That means my OD ratio is higher than his (AUTO is a .84, Standard is a .79).

I have no problem driving 45 MPH at 1100 RPM's in 6th gear. There is very little strain on the engine, and at that rate I'm getting well over 25 MPG. I can do that all day, and only have to downshift for an incline, and I would downshift to 5th and turn 1600-1700 RPMS and climb just fine.

I'm still on the 255/75/17 SRA's, which measure 31.5 mounted. His 33's will be around 32" depending on the brand. The higher RPM's of the 4.11 gears would be more strain on the engine. With a performance tune, the engine will be working more towards its maximum potential regardless of gears. Pair a tune WITH lower gears, and it'll REALLY be working that engine.

 

thanks for the insight fellas

so, looks like - stay away from tuners/programmers - if / when they come out for the 12
save the cash, and do a re-gear
figure what ratio to go with

going to the biger tires (+ 3-4"..29" upto the 33")
i would want to maintain at the very least...the power i have now, but would liek tohave a little more, get up n go, off the line
not kill the engine
and maintain decent highway usage

granted, in the future, i also plan on a level/lift and new bumpers (steel)
so im assuming, going to 4.11's - to compenstae for the tire size, added weight of the bumpers and add'l height of the level/lift

 

Sorry but you are wrong. Most load will be placed on the engine during takeoff and acceleration, as well as inclines such as going up hills. Highway driving on flat terrain doesn't place much load on the engine once the vehicle is moving. Lower gearing will keep the motor closer to its optimal powerband, which will provide more torque which is needed to lessen the load on the engine

 

The OP's question was "which will put more strain on the engine." I answered " A tuner."

As to the gear thing, more RPM's is nearly ALWAYS more strain on the engine. A 2012 Auto Transmission with 3.21 gears and 33's is NOT going to have a problem getting going from a solid stop. He won't have the performance that higher gears have, but the engine strain will still be less. It all boils down to how much fuel is burning. More RPM's will burn more fuel, and result in more power. Lower RPM's will result in less fuel, and less power. Running higher RPM's will reduce the life of the engine.

I found a chart I will link - it shows an average RPM to Engine life comparison using several different engines.

With the AUTO JK's 2007-2011, I think I would have to agree that the 3.21's would be pretty awful for the 33's, but that is because of the .69 OD ratio on the Automatic for those years. At that ratio, even the new Pentastar engine would most likely have trouble turning tires at +65 mph.

I can compare to a Chevy V8, which I owned before my JK. Even with as much power as it kicked out, the motor had problems with larger tires, but it was because of the very high OD ratio, not just HP & Torque. That said, get up and go suffered some, but the reason to regear the axles was not for 0-60 power, it was for +65 driveability.

http://www.metricmechanic.com/catalog/engine-life.php