my jeep is an 07 black unlimited sahara.
it came stock. then moved to 35s, intake, bumper and winch, highlift...that kinda stuff.
i mudded it and messed a few things up....then about 6 months after all of that, as of last week..i swapped down to 33s (which are bald) just to see how it looked before i bought a new tire...

i like the 35s on there, but the smaller tires drive alittle better, and its little more responsive and peppy with them..but i think it looked better...

major reason for the swap was gas...i know, if i wanted good mileage, dont get a jeep. but i wanted the jeep.

if i put the 35s back on what would be some ways to make it drive better, and get better gas?

some things ive heard: recalibrate and chip, exhaust (dual or single?), different rims so i can take the wheel spacers off, gears and so on. could u guys explain what would be the best as far as money and the difference each would make? prioritize i guess....


oh, and ive noticed my jeep sounds alittle funny im not sure what it is...sounds like its chuggin....like a tractor? im not sure...

but anyways thanks for the help, really appreciate it.

 

From what I've read on here it sounds like maybe time to regear & recalibrate, the other things didn't appear to affect mileage that much.

 

how would 5.13s change how it drives?
how it tows, highway and city...that kinda thing

 

You need bigger gears to turn those bigger wheels... You got 4.10 like me I would think. You running 35 inch all terrain tires or mud tires? When these 33's I got wear out I am thinking 35 AT tires..

 

Don't expect your mpg to go up after a regear. I was getting about 17 highway after the lift and 34" tires. It was a little sluggish, but ok in the flatlands. I installed 513 gears and I got all of the performance back and then some, but the mpgs dropped to 15 give or take. As a side note, everytime I or my dealer has regeared anything to a higher ratio, the performance increased and the economy went down. Also, I had my best ride when it was stock. I'm ok with all of that. I didn't buy the jeep for its ride or economy. If you go with the 33s, your economy will go up and you won't have to regear for performance. It all depends on what you want your Jeep to be.

 

Very well put !

The 5.13a and 35s are the ticket! In my opinion the 5.13s make the jeep drive prob a little better than stock. The performance is better, the 4WD (espcially in 4L) is AWESOME.

But as far as mpgs....its a Jeep. I metal box with 40 year old tech...what do you expect?

 

If you haven't calibrated your speedometer, you are understating your fuel mileage by nearly 10% whether your using the dash mpg gauge or hand calculating.

Secondly, without having your speedometer calibrated on an automatic, your shift points are off resulting in shifting into an rpm range which doesn't supply an appropriate amount of power to sustain your speed. To clarify, 3 things go into determining shift points, manifold pressure, throttle position and speedometer. Where you end up is essentially bogging things down, then unlocking the converter and eventually downshifting. That is the real killer of fuel mileage and efficiency.

Everything Planman stated is right on the money you really need to strongly consider getting a new set of gears. You're still going to need a programmer of some sorts so the computer understands what's attached to your vehicle and a set of gears without one just leads to another set of issues. The other alternative and a temporary fix is to get a programmer so your shift points are correct and turn overdrive off. That gets rid of the 0.69 4th gear and helps keep your JK in an appropriate rpm range.

 

Not to hijack this, but I think it applies. I have the superchip and have corrected for gears and tires. My speedo is right on with the GPS and a timed run between mile markers at 60 mph. If I run a steady 60 mph on flat ground and no wind, (which is the speed I drive anyway) I can get 16 mpg. 70 will bring it down to the low 15s. Before I regeared to 513s, I would get close to 18 at the same steady 60 mph speed. I've tried the different superchip settings with little change in the mpg. I'm currently running the 87 octane setting which seems to be as good as any. I tried the 91 & 93 options, but I don't need anymore performance than the 87 and there was no change in mpg. Why don't all gear changes have the same general result, either an increase or decrease in economy?

My motorhome has 2 overdrive gears. I'll get 9 mpg in 6th gear @1550 rpm and 8 mpg in 5th gear @1850 rpm. That's a similar result as the Jeep at higher rpms. More power, but less economy. I'm puzzled!

 

OK, flat ground and no wind takes away a lot of the downshifting and unlocking of the converter. This is the largest culprit for poor fuel efficiency. With your change in gear set you have increased your rpms by 25% and degraded your fuel economy by less than 12%. With 34" tires and an automatic, 4.88 gears would have been an acceptable combination, especially since you seem to be in a situation with plenty of flat land and a lack of wind. Furthering this lack of fuel economy could also be the actual size of the tires. They are probably in the 33" range in actual tire height and with wider wheels might even find themselves measuring closer to 32".

Record your actual rpms at 60 or 70 mph. Note what size your tires are set at in the Flashpaq. Do a physical measurement of your tires from the ground to the top of the tire, do not measure the spare.

With those numbers I can lend a little assistance and under the circumstances that you drive under your gear set might be a little steep. You might actually find yourself in a situation where increasing your tire size would reduce fuel consumption by lowering your rpm, and you are obviously making more than enough power to sustain your speeds.

When I built out the gear chart seen in the FAQ, I tried to make accommodations for different scenarios and usage. Where Planman travels is quite different than where I am with him having a couple thousand extra feet of earth under him with thinner air and more hills encountered in a day than I will see in a month.

Anyway, here's the chart from the FAQ and perhaps the best answer is doing this a little backwards from the majority of people who are looking for a gear set to match their tire size and approach it from the perspective of getting a tire size to match your gears.

 

The measurement that I use for the superchip is from the ground up to the hub, as that is the rotating diameter that the speed sensor picks up. That distance for my 305X70R17 MTRs w/k (calculated 34.1") is 16"s at 30 psi. I suspect a 315X70R17 (calculated 34.8") would be close to 16.4". Hense, my 34s have a 32" rolling diameter and a 35" would be 32.8". So, 2 X 16=32". That is the number that matches the gps. I've often wondered if the higher mpgs reported are with measurements from the ground up to the top of the tire, which would tell the speed sensors a longer distance and thus higher mpgs. As I recall @ 60 mph= 2150 rpm and 70=2530 approx. I've already thought about going to 37s for the ground clearance. Might be kind of costly with only 3000 miles on mine.

I went with the 513s because 90% of my offroading will be in AZ in the mountains and not in flat central WI.