What are the fuel consumption implications on regearing a 3.8 auto Rubicon? Going from stock to either 4.88 or 5.13?

 

The direct implication is that if you are regearing to install larger tires your fuel economy will go down.

How much is hard to predict because fuel economy is all over the map to begin with, but individual driving habits, local fuel, local terrain, etc all play a factor. Another important factor is you will use a PCM programmer or not.

Run a search and peruse the many threads on gas mileage and you will get a rough idea.

 

I already have 33's, so mainly considering regearing to get the auto box to work better and performance, and hopefully better fuel consumption?

 

I've been wondering the same thing......Regear, Superchips, or both to bring back life in the motor after stuffing in 35's

 

I've tried SC as well, it changes driveability, but makes no fuel consumption difference.

 

My implications would be that if you're worried about mileage, buy a Toyota. The gas pedal might stick, but you'll get great mileage doin it.

 

Totally, my wife has a rav4, way more HP, way better mileage. It is not a Jeep.

 

Don't be surprized if your mileage gets better.

https://www.jk-forum.com/forums/jk-talk-26/gearing-ratios-gas-mileage-122544/

Try to find that gearing chart and shoot for the "middle of the road" gearing for your setup.

 

First thing to help your mileage is get your speedometer corrected with an automatic if you haven't done so. Shifts are determined by throttle position, engine rpms and speed, so if the speedometer is off, so are your shifts. It doesn't matter what tool you use to get it done, be it an AEV ProCal or Superchips.

With 4.10s and 33s you aren't severely under-geared, but close. Getting the appropriate gear set underneath will help prevent some downshifts, which rob fuel economy by unlocking the converter and higher revs. 4.88s at minimum would be the right call unless you have your sites set on some bigger meats.

 

FYI - I just installed 5.13'S. I have an auto and 35 in tires and had 4.10's. Corrected, manually calculated mileage has increased about 1 to 1.5 mpg. Most of my driving is in the mountains (very little freeway). I have a programmer and the speedo and gearing have been reprogrammed. The Jeep is also much more enjoyable to drive.