LOST JEEPS :: View topic - When to change diff ratio??

I'm wondering when you need to start to consider changing your diff's gear ratio. As I know nothing about it & have gone to a larger tyre & steel rims I wondering if I should be considering it or not. 265/70/16 on 16X8 soft 8's with 4.5" BS, so it's much the same in height as a 245/75/16 but with more weight and stress. I'd prefer to leave it as is & so far I've not noticed any problem with wheeling, perhaps I use low range sooner than before but it's all good.

Can anyone offer any advice or put my mind at ease.

CDKJ wrote:

We run 245/75 's on our gasser with no issues
I would like to gear it to 4.10 but I am a slow go crawl it nut so I am biased
as far as 4hi to 4lo I can not say
we follow the rule
if you are on a TRAIL and need 4wd the you SHOULD be in 4lo
that being said in 4lo you can go slower and have more control on what and where your wheels go on and over
we NEVER run trails in 4hi wich may be why we dont realy need to regear
3.73 on 31" tires is about the same as 4.10's on 33's and guys with rubi's run 33's all day long
but they have 4 to 1 in the T-case

You also need to look at how much low end torque your engine is producing.The I-6 in the TJ won't be as effected as the V-6 in the KJ,the 4.0 makes more low end torque then the KJ's V-6.If you have a desiel it will be less effected to a point.You are right about the t-case gearing,you can get away will a little higher diff gears if you have a lower 4-low ratio in the t-case.I can't wait for the 4.3:1 reduction from the AtlasII t-case and 5.13 diff gears.

day long
but they have 4 to 1 in the T-case

Author:	CD [ Sun Sep 30, 2007 7:09 am ]
Post subject:	When to change diff ratio??
I'm wondering when you need to start to consider changing your diff's gear ratio. As I know nothing about it & have gone to a larger tyre & steel rims I wondering if I should be considering it or not. 265/70/16 on 16X8 soft 8's with 4.5" BS, so it's much the same in height as a 245/75/16 but with more weight and stress. I'd prefer to leave it as is & so far I've not noticed any problem with wheeling, perhaps I use low range sooner than before but it's all good. Can anyone offer any advice or put my mind at ease.

Author:	tjkj2002 [ Sun Sep 30, 2007 9:03 am ]
Post subject:
This chart may help a little----- http://www.4lo.com/calc/geartable.htm

Author:	jason thompson [ Sun Sep 30, 2007 7:02 pm ]
Post subject:	Re: When to change diff ratio??
CDKJ wrote: I'm wondering when you need to start to consider changing your diff's gear ratio. As I know nothing about it & have gone to a larger tyre & steel rims I wondering if I should be considering it or not. 265/70/16 on 16X8 soft 8's with 4.5" BS, so it's much the same in height as a 245/75/16 but with more weight and stress. I'd prefer to leave it as is & so far I've not noticed any problem with wheeling, perhaps I use low range sooner than before but it's all good. Can anyone offer any advice or put my mind at ease. We run 245/75 's on our gasser with no issues I would like to gear it to 4.10 but I am a slow go crawl it nut so I am biased as far as 4hi to 4lo I can not say we follow the rule if you are on a TRAIL and need 4wd the you SHOULD be in 4lo that being said in 4lo you can go slower and have more control on what and where your wheels go on and over we NEVER run trails in 4hi wich may be why we dont realy need to regear 3.73 on 31" tires is about the same as 4.10's on 33's and guys with rubi's run 33's all day long but they have 4 to 1 in the T-case

Author:	tjkj2002 [ Sun Sep 30, 2007 8:00 pm ]
Post subject:	Re: When to change diff ratio??
jason thompson wrote: CDKJ wrote: I'm wondering when you need to start to consider changing your diff's gear ratio. As I know nothing about it & have gone to a larger tyre & steel rims I wondering if I should be considering it or not. 265/70/16 on 16X8 soft 8's with 4.5" BS, so it's much the same in height as a 245/75/16 but with more weight and stress. I'd prefer to leave it as is & so far I've not noticed any problem with wheeling, perhaps I use low range sooner than before but it's all good. Can anyone offer any advice or put my mind at ease. We run 245/75 's on our gasser with no issues I would like to gear it to 4.10 but I am a slow go crawl it nut so I am biased as far as 4hi to 4lo I can not say we follow the rule if you are on a TRAIL and need 4wd the you SHOULD be in 4lo that being said in 4lo you can go slower and have more control on what and where your wheels go on and over we NEVER run trails in 4hi wich may be why we dont realy need to regear 3.73 on 31" tires is about the same as 4.10's on 33's and guys with rubi's run 33's all day long but they have 4 to 1 in the T-case You also need to look at how much low end torque your engine is producing.The I-6 in the TJ won't be as effected as the V-6 in the KJ,the 4.0 makes more low end torque then the KJ's V-6.If you have a desiel it will be less effected to a point.You are right about the t-case gearing,you can get away will a little higher diff gears if you have a lower 4-low ratio in the t-case.I can't wait for the 4.3:1 reduction from the AtlasII t-case and 5.13 diff gears.

Author:	CD [ Mon Oct 01, 2007 5:50 am ]
Post subject:
Thanks guy's, so it would seem as per the chart that 3.37 gear ratio (stock) on 30.7" tyres (I think that what mine are on 8" wide rim) will use more petrol than a higher gear ratio. But it's not that far out that it should be a problem, what's interesting is that that the stock size tyre on that chart shows that a 4.1 ratio would be better when in low range anyway so it should be fine. What are some of the potential issuse you can have with an under powered diff: Overheating engine Break the CV's Break the Diff Would these be on the list, I'm only asking as it can help to understand a little more about you KJ and it limits, and in turn determine how you drive your KJ I've got to admit that I get a bit lost when trying to comprehend all this sort of talk . Quote: You also need to look at how much low end torque your engine is producing.The I-6 in the TJ won't be as effected as the V-6 in the KJ,the 4.0 makes more low end torque then the KJ's V-6.If you have a desiel it will be less effected to a point.You are right about the t-case gearing,you can get away will a little higher diff gears if you have a lower 4-low ratio in the t-case.I can't wait for the 4.3:1 reduction from the AtlasII t-case and 5.13 diff gears. & Quote: day long but they have 4 to 1 in the T-case I supose my problem is (as perhps like many) I just like to drive the KJ, I've often said the great thing about the petrol KJ is you just fill it up and drive it. However I'm comming around & kind of have to as I want more out of my KJ.

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Author:	wendell [ Mon Oct 01, 2007 5:43 pm ]
Post subject:
With only a 31' tire and an automatic, the 3:73's should be fine unless you do alot of extreme wheeling and not on the highway much.

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