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Regearing Questions? READ THIS!

BTT for a brand new crop of newbs.....

CRASH
 
First, this is a great thread and I was happy to see that part of this info was turned into a sticky. One thing that wasn't covered, maybe on purpose, is brand. Are there some brands of gears that are better than others or are they pretty much the same?

clay
 
clay said:
First, this is a great thread and I was happy to see that part of this info was turned into a sticky. One thing that wasn't covered, maybe on purpose, is brand. Are there some brands of gears that are better than others or are they pretty much the same?

clay
Click to expand...
Avoid Genuine Gears.
 
BTT for another generation of noobs.
 
what the hell are you suppose to do with a calculator
 
xjwillyb said:
Didn't see this calculator, hope it's not a repost...

http://www.dfw-tx4wd.org/gears.html

Will.
Click to expand...

Calculators are deceiving: they do not take into account the weight change from stock to modified, the height change which is directly related to increased air resitance and so on...... The only thing that they should be used for is to see what RPM's you will end up at after you regear with your tires at your top expected speed. That whole thing for best performance best fuel efficiency is really someone just theorizing the what ifs (just like based on that theorizing my hybrid should be getting about 15mpg more then it does)
 
why do you always have to be so nice and explain things to everyone :)
 
Ramsey said:
what the hell are you suppose to do with a calculator
Click to expand...

I realize (as should everyone) that there is NO 100% accurate answer... Just thought it might help some understand what might occur with gearing changes...

Maybe if ya stare at the screen it'll read your mind, and cure the world of hunger... JK

Will.
 
to the top!

lots o gear questions in mod tech right now...
 
I have a 98 XJ with the 8.25" rear end and 31" tires. I don't think the previous owner ever changed the gears, so I am guessing they are still the stock 3.55s. I had been eyeing the 4.10s. Sounds like I need to add that to my list along with the correct shocks for 4.5"s of lift. (It has 3" lift shocks on it now :confused:)

This has been an incredibly helpful site! Just wish I knew of it earlier.
 
groovyone said:
This has been an incredibly helpful site! Just wish I knew of it earlier.
Click to expand...

We aim to please......
 
Well, I am getting a little bit confused on this. I have a 1988 with a 4.0 engine, manual transmission and thus crappy 3.07 gears. I'm actually driving with 30 tires, but I'm planning to replace my budget lift (between 2 and 3 ") for a 4.5" lift, so I might use up to 32 tires. Now, my calculations give me the following:

Stock tire is about 26.8 / 3.07

So calculating, I should use:

30 tire - 3.43, that means 3.56
31 tire - 3.54, that means 3.56 again
32 tire - 3.66, that means 3.78
33 tire - 3.77, again 3.78

This is a simple calculation, however my XJ is a daily driver and I drive it up to 90mph, and I get up to 21mpg on highway, and at least 16 mpg in the city, and I don't want this to change dramatically.

So, I have two moves, go with 3.56 gears thinking of my 30 tires (these gears will be cheap as everybody with an auto tranny wants to get rid of them), or go directly to 3.78 or even 4.10 to definitively forget about future regearing.

I have read that the same gear ratios for auto trannys are recommended for manual trannys, but it doesn't make sense to me, I do alot of offroading (not really extreme off-road driving), and I have no real trouble with my 3.07 gears, I rather want to regear to gain torque on highway driving, and obviously get the benefits off-road. I will hardly go for tires over 32, if I did want such tires, I might choose another vehicle (not because I underestimate the XJ).

However, my issue is just to decide the proper gear ratios which will NOT hardly affect the gas mileage even with 30 tires. It would be great to hear from similar experiences. :D

Regards
 
Last edited:
schmiedel said:
33 tire - 3.77, again 3.78
Click to expand...

I run the same setup as you - 4.0L, manual, stock t-case

I had 3.07's on 235/75's (abour 29.5) and then swaped axles for a set of axles that had 3.55 gears -

I loved the 3.55's with the 235's

I slaped some 33's on there, and it now feels like it is a little under-geared, a little worse than stock.

My gas mileage is about 15-18

4 low is not low enough at all...
 
OK, this experience seems to me as if I should forget the default setup (26.7 and 3.07) and rather consider 30 and 3.56 as a good setup and start from there, right? This will definitively lead me to install 4.10 gears. I will check how much I will have to pay for labour for the 3.56 gears, if I can sell the 3.07 for a good price I might do it as an intermediate step. Thank you for your experiences...

Regards
 
My wife's rig runs 30" tires and 3.55's, and she despises it. Always hunting between Drive and Overdrive in the mountains where we live. I'm going to switch her to 4.10.

In the flats, 3.55's and 30's would be fine.
 
Thanks... In fact, 3.55 on an auto is the same as 3.07 on a standard, and I also have trouble on steep hills with the 3.07 gears and 30 tires, that's why I'm upgrading...However, my last question is about the first message of this thread. Do you all really think that auto and manual should be geared equally? If so, why?

Regards
 
CRASH said:
My wife's rig runs 30" tires and 3.55's, and she despises it. Always hunting between Drive and Overdrive in the mountains where we live. I'm going to switch her to 4.10.
Click to expand...

30's and 4.10's is a good combo IMO. Thats what I run. (4.0, AW4)

I would like to go 31's once the 30's are bald. I think I'll still be good though.
 
schmiedel said:
Thanks... In fact, 3.55 on an auto is the same as 3.07 on a standard, and I also have trouble on steep hills with the 3.07 gears and 30 tires, that's why I'm upgrading...However, my last question is about the first message of this thread. Do you all really think that auto and manual should be geared equally? If so, why?

Regards
Click to expand...


The OEM manuals in XJ's have a much shallower OD than the Auto's. Depending on year, the manuals have around a .80 OD, while the autos have .69-.73. You can easily get away with a deeper gear on the auto, as they drop the revs an additional 200 or so RPMs over the manual.

The catch is, you really need deeper gears offroad in a manual than an auto, due to the auto's converter slip. For instance, you could get away with 32's and 4.10's in an auto, but for a manual, you'd want 4.56's.

Again, though, as I've said in the first post, don't be afraid to spin the little 4.0, it is quite happy at 3,000 RPM all day long.

So in the end, it'll cost you a few hundred RPM, but manuals and autos should be geared the same if we are talking about a good combo of on and off road performance. If you are more inclined to off-road, I'd gear a manual deeper.
 
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