Originally Posted by patmcd44

You should be fine if you already have the 4.88, however if you haven't done the gears yet and plan to go to 37's, definitely the 5.13 is your best choice with a manual transmission.

Originally Posted by SilverJK12

Yes, I already have the 4.88. Seems like 5.13 would be too much for manual and 37s especially on the highway

Originally Posted by racin444

According to you sig youre running 35s though. 37s are way bigger than 35s so if you like 4.88s on 35s then 5.13s are the way to go with 37s.

Originally Posted by planman

That chart is very misleading because it is based on a manual transmission gear ratio of 1.0. It leads people to under gear their rigs.

Quote: These calculations are assuming a manual transmission with a 1:1 ratio

Automatics have a 4th gear (overdrive) ratio of 0.69.

6 speeds have a 6th gear ratio of 0.84.

The experienced jeepers (who have driven different setups with different gear ratios) nearly always give unanimous answers:

With a non-supercharged engine:

An automatic on 35s or larger should run 5.38s if they drive mountain passes, live at higher elevations, tow anything, or ever plan to upgrade to 37s--especially if they drive a 4 door.

An automatic on 35s that lives and wheels at low elevations, doesn't drive steep grades, or doesn't tow anything should run 5.13s.

A 6 speed on 37s should run 5.13s, and maybe 5.38s if they don't spend much time over 65 mph.

A 6 speed on 35s that is either a 4 dr, or drives at high elevations, tows, or drives steep grades should run 5.13s.

A 6 speed on 35s that is a 2 door and will never upgrade to 37s, or a 4 door that lives and wheels at low elevations and almost never tows should run 4.88s.

There is very minimal debate about this among guys who have had the experience of driving different setups with different gear ratios. They guys who suggest otherwise usually have never driven or experienced different gear ratios.

The shops discourage the 5.13 and 5.38 gears because they don't understand our engines only produce 64 rear wheel horsepower 169 torque at 2000 rpm, at 2500 rpm they produce 88 horsepower and 184 torque, and at 3000 rpm they produce 107 horsepower and 188 ft lbs of torque.

They don't understand that automatics have a 4th gear ratio of 0.69. These mini-van engines need higher rpms to produce enough horsepower and torque to turn heavy 35"+ tires--especially up steep freeway grades or at higher elevations.

Okay, rant over. It is just that every time I see that table on quadratec, 4wd, and other websites, it reminds me of all the folks who wasted $1000-$1500 to gear to the wrong gear ratio--then they believe they need to spend more money on engine upgrades (superchargers, cold air intakes, headers, etc.) because they are not satisfied with the weak performance of our engines at rpms under 2500-3000. They don't even get that the table is based on a 1.0 transmission gear ratio for a manual transmission. They could have almost doubled their rear wheel horsepower if they had just properly geared their rigs to run 3k rpm at freeway speeds.

Originally Posted by JPop

Well, here's a preliminary one.

I think it's pretty good guideline and I tried to break things down a little differently than some of these other charts. I also did away with the red they used as I thought it had a negative connotation for what isn't a poor choice, but one that means a good choice for performance.

On the yellow fields and what I determined to be the bottom end of the gear/tire combinations I would note that these are not gear sets that you would want to upgrade to, but rather what you could get away with if you decided to upgrade your tire size.

Whenever you get to tire sizes of 35" and beyond it's best to look to the high side of the green fields or better. This is primarily because I believe the majority of people that take on the expense of 35s or better really do have more intent than just driving around the mall.

This certainly isn't a done deal nor by any means something that isn't open to criticism. I used the dyno information available to determine where enough torque existed to get a vehicle rolling and enough hp to sustain highway speeds.

All RPM numbers are at 70mph.

Originally Posted by patmcd44

You should be fine if you already have the 4.88, however if you haven't done the gears yet and plan to go to 37's, definitely the 5.13 is your best choice with a manual transmission.

Originally Posted by Jeep Hound

This is by far the best chart Iv seen.