Help With Gear Ratio

[TheDirtyJeep401]

Ive decided the size tires that I want are 33x12.5R15 and I was wondering what kind of gears I should get.

[MJCARENA]

On my 89 XJ with 33's and an automatic I run 4.56 gears and I like them.

[TheDirtyJeep401]

Wonder what they would be like behind a 2.5

[88whitemanche]

I have the 2.5 ax5 with 4.11 gears with 32x11.5x15 and today I was spinning my tires with ease. Gas mileage is the same as before.

[TheDirtyJeep401]

I have the 2.5 ax5 with 4.11 gears with 32x11.5x15 and today I was spinning my tires with ease. Gas mileage is the same as before.

Be looking at that ratio, thanks for sharing

[mnkyboy]

I have 4.88s with a 2.5l and AX4 turning 33x12.50-15s.

 

On the road it feels slightly over geared and I could definitely make use of a 5th gear but otherwise its great.

 

I would look at 4.56 or 4.88s

[TheDirtyJeep401]

I have 4.88s with a 2.5l and AX4 turning 33x12.50-15s.

 

On the road it feels slightly over geared and I could definitely make use of a 5th gear.

 

I would look at 4.56 or 4.88s

I was looking at 4.56 gears too they seemed about right too.

[87Warrior]

The 235/75r15's make my' 86, 2.5, ax5, 4.10 feel like a dog. 33's would be unbearable, for me at least, with the stock 4.10 gears. The 2.5 is more high strung than the 4.0 so I would tend to error on the over gearing side of things. I think 4.88's would be a good fit for 33's and the 2.5/ax5. 

[onlyinajeep726]

This should help.

 

[Geonovast]

Is that chart specific to our motors?  It also doesn't specify if that's axle ratio or final drive.

[TheDirtyJeep401]

Is that chart specific to our motors?  It also doesn't specify if that's axle ratio or final drive.

Was starting to think the same thing

[onlyinajeep726]

I forget where I found that chart specifically, but IIRC, it's specific to the 4.0L/AW4 auto in 4th/overdrive.

 

It similar to this one, which goes into detail how they calculated the values...

http://www.superlift.com/library/gears.asp

 

This one may also be of some help:

http://www.jeepforum.com/forum/f13/zj-forum-faqs-read-before-you-post-880249/

[TheDirtyJeep401]

Wait, you have to have an 4.5 lift in order for the tires to fit?

[mnkyboy]

At least 4.5" and you may still need some trimming. People have done it with less and a ton of trimming.

 

My truck is lifted about 7" with alot of trimming.

[Eagle]

This should help.

 

 

Those numbers don't even say what they represent. Is that supposed to be RPM at 60 MPH? If so, is that in top gear (overdrive) or 1:1 ratio (4th in the 5-speed, 3rd in the auto)?

 

Assuming they represent RPM at 60 MPH, they are completely wrong. I compared them to the numbers I worked up in a spreadsheet, using actual tire manufacturers' revolutions-per-mile data, and the numbers in this chart simply don't match up with ANY RPMs in my spreadsheet.

 

The above chart is somewhat useful as a general guide (bigger tires = less RPM, more gear = more RPM), but not helpful beyond generalities.

[TheDirtyJeep401]

At least 4.5" and you may still need some trimming. People have done it with less and a ton of trimming.

 

My truck is lifted about 7" with alot of trimming.

well crap, I thought I would get away with a 3 in lift

[Bounty Hunter]

Is that chart specific to our motors?  It also doesn't specify if that's axle ratio or final drive.

It doesn't matter.  Find your stock gear ratio and tire height.  Note the listed RPM.  Move down to your new tire height and move to the right until your find the RPM close to what you found with the stock setup.  Then look up to the new recommended gear ratio.  I recommend going one ratio lower (numerically higher) if possible, as the chart accounts for increased tire diameter but not increased tire mass.  Erring on the low ratio side greatly improves performance on road and off.

 

The common stock ratio for the 2.5L AX5 setup is 4.11, so I'd definitely go with 4.88 gears.  Changing to 4.56 isn't enough of a change to warrant the cost and time involved, and performance will only be slightly improved.

[Darren]

Yes. Go with 4.88s.