Best Gears For 31" Tires???

[GregGA]

I've got 31's and 4.56. They are IMO, perfect. Don't waste your money on 4.10's.

 

[yaromb]

32s with 4.11 is correct..

 

[Frank Z]

^^^yep^^^

 

[escout]

This is a great chart.

It seems that using 4.10's and a 32 (31.7") tire puts the rpm back to OEM range, which if great for us guys who DD. I don't want to be spinning sky high at 70mph, so that is my plan. 4.10 with a 32 in tire.. that will work well for me on and off road. If I was in a higher elevation like the OP, I would have done the same as him.. 4.10 with 31" tires to give it a little extra grunt.

Even though I just got those gears installed, that was a pretty sweet chart! I'm sure it'll come in handy for some later gear swap!

 

[blondejoncherokee]

you'll be happiest with 4.56 or 4.88. That gives you room to grow with bigger tires...

 

[markw]

It's all good on paper, but in reality the deeper gears with 4.56's do make a difference even on 31's. It's web wheeling vs real wheeling.

 

[yossarian19]

4.10 and 32's are geometrically correct but the added mass means they'll spin up slower... this is why most folks recommend 4.56 gears above 31" tires.

 

[Tony_SS]

I think those are the guys who do a lot of off road, and really don't care about spinning 3k at 65mph.

 

[notamos]

I'm running 4.56 with 31s (BFG AT, Auto trans). Here in CO, I wouldn't trade it for anything. It does *not* rev too high although, if you have anything in your driveline out of balance - it will vibrate...

 

[Rod Knee]

I think those are the guys who do a lot of off road, and really don't care about spinning 3k at 65mph.

With the auto transmission rpm's are 2600 at 65 mph, which is not excessive.

 

[markw]

It is a jeep not a sports car. 65 is about all the faster I care to drive mine. 2300rpm at 70 btw. 33's and 4.56's 31's would be about 100rpm higher.

 

[Tony_SS]

Post 16 tells a different story.

 

[techno1154]

Post 16 tells a different story.

I think post #16 is accurate. I am running 30" BFG AT and 4.10 gears and see about 100 RPM more at the same listed MPH. I will be changing to 31" soon and hoping to see about 100 RPM less at the same speed.

Do you think that something is wrong with my 4.0L engine? It do not like high RPM's. Yes it will turn up to 5,000 RPM with out a fuss but so does the gallons per mile. Keep the RPM below 2,700 and it will return 19+ MPG all day long.

 

[Tony_SS]

According to the chart 4.56 with 33's will spin 2460 at 70 which doesn't sound too terrible.

 

[Rod Knee]

I've done some verification testing of the output of that chart on 31's, both with 3.55 and 4.56 gear ratios. Based on my results, the calibration of that chart is not exactly spot on. I get closer numbers to the charts output by inputting actual tire diameter rather than nominal diameter, but even then its a bit off. My observed real world RPM's are about 200 higher than the chart output numbers for the nominal tire size. That is testing with my XJ, YMMV.

 

[Tony_SS]

My results above used the actual tire height. But to that does sound too good to be true.

People assume their speedily is accurate too. They need to use a gps to determine actual ros at a given speed.

 

[Gary Briggs]

Correct me if I'm wrong, but my 4.0l with a manual comes with 3.07 gears. I'm currently running 31" BFG's and about to do my gears at the same time as my 8.8 swap. The 8.8 has 3.73's in it and based on my research I thought this would be ideal with my manual transmission.

I can only assume the people running 4.10's and 4.56's must be auto tranny guys?

My jeep only sees moderate offroad use in the Sierra Nevadas, no rock crawling. To be honest I have no problems offroad in low range, I'm just looking to avoid the rare instance where I have to down shift into 3rd on a steep grade on the way to the trails.

Appreciate any feedback.

 

[ingenio]

Correct me if I'm wrong, but my 4.0l with a manual comes with 3.07 gears. I'm currently running 31" BFG's and about to do my gears at the same time as my 8.8 swap. The 8.8 has 3.73's in it and based on my research I thought this would be ideal with my manual transmission.

I can only assume the people running 4.10's and 4.56's must be auto tranny guys?

My jeep only sees moderate offroad use in the Sierra Nevadas, no rock crawling. To be honest I have no problems offroad in low range, I'm just looking to avoid the rare instance where I have to down shift into 3rd on a steep grade on the way to the trails.

Appreciate any feedback.

The 8.8 comes in 4.10 flavor as well...and it is not unusuall to find them in the yj
I intalled 4.10 w 265/75/16 and it's just OK, its an aw4 & 4.0 .

A friend runs 31s with 4.56 and I really like it...noticeable increase in low end grunt and negligible real world mpg adverse impact....

 

[Gary Briggs]

The 8.8 comes in 4.10 flavor as well...and it is not unusuall to find them in the yj
I intalled 4.10 w 265/75/16 and it's just OK, its an aw4 & 4.0 .

A friend runs 31s with 4.56 and I really like it...noticeable increase in low end grunt and negligible real world mpg adverse impact....

I got my 3.73 8.8 with serviceable disc brakes for 90$, so beggars can't be choosers.

I don't have any problem with flat land drivability on the 3.07 with a manual and the 31's. Like I said the problem is pulling a long grade.

It seems like 3.07 to 4.10/4.56 is a huge jump, I don't have any intentions of ever running bigger tires than the current 31's.

Does anyone with a MANUAL TRANSMISSION have any input?

 

[Hellbent]

having driven 31's with 3.07's, 4.10's, and 4.56's in a manual(as well as with 235's, and 33's)...
31's w/ 4.10 in a 5sp is a great combination for the all around daily driver. I use(d) my xj as a DD and wheeler, driving semi-regularly to L.A. and sometimes farther.
4.56's were a little deep for extended 70mph+ use.
If I were to do it again, and was going to stay with 31's in a daily driver, I'd do 4.10s again without a doubt.
everyone has a different opinion. I think 3.07's + 31's is awful, but some others think it's ok. My new AW4 xj will get 4.56's w/ 33's, also DD/weekend warrior use.