4.88s with 40s and 4:1 tcase

Braxtonsag

Braxtonsag

Member
Before I get screamed at about how 5.38 is the correct ratio for 40s hear me out.

I bought my jeep with 3.21s and 29” tires and I really didn’t mind the way it drove. It had plenty of power and got the job done. Fast forward a bit and I was eventually running 4.88s with 37s. I kind of despised how over geared the jeep felt and moving up to 38s was a breathe of fresh air although it still feels a bit over geared on the highway. I’d like to move up to 40s and going by the infamous jk gear ratio chart I would STILL be overgeared compared to how my jeep came stock.

The only downfall to this is that I think with my sport tcase, 4 low wouldn’t be ideal and I would need to source a rubi tcase. On the brighter side, I’ll have much more pinion to play with than on a 5.38 in my dana 44s. I’m fully aware dana 44s aren’t the ideal axle for 40s but I’m more of an explorer rather than a hardcore rock crawler. They will suit me just fine.

Anyone have any input on this gear and tire combo? Should I stick to this plan or bump up to a 5.13? Probably going to be a matter of opinion but wanted some insight from you guys anyways.

I’ll attach the gearing chart and I have circled how my jeep came, where it is now, and where it will be after 40s.

3FAFA41A-C4C5-456B-9D3E-4814AFC88575.jpg
 
Braxtonsag said:
Before I get screamed at about how 5.38 is the correct ratio for 40s hear me out.

I bought my jeep with 3.21s and 29” tires and I really didn’t mind the way it drove. It had plenty of power and got the job done. Fast forward a bit and I was eventually running 4.88s with 37s. I kind of despised how over geared the jeep felt and moving up to 38s was a breathe of fresh air although it still feels a bit over geared on the highway. I’d like to move up to 40s and going by the infamous jk gear ratio chart I would STILL be overgeared compared to how my jeep came stock.

The only downfall to this is that I think with my sport tcase, 4 low wouldn’t be ideal and I would need to source a rubi tcase. On the brighter side, I’ll have much more pinion to play with than on a 5.38 in my dana 44s. I’m fully aware dana 44s aren’t the ideal axle for 40s but I’m more of an explorer rather than a hardcore rock crawler. They will suit me just fine.

Anyone have any input on this gear and tire combo? Should I stick to this plan or bump up to a 5.13? Probably going to be a matter of opinion but wanted some insight from you guys anyways.

I’ll attach the gearing chart and I have circled how my jeep came, where it is now, and where it will be after 40s.

View attachment 338518
Click to expand...

Might be only person I’ve ever heard say 4.88 with 37s is over geared . It’s what I run and while it’s fine .. certainly not over geared



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fiend said:
Sounds like you’re pretty confident 4.88s will be fine. Why not give it shot. You can always regear later.


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Click to expand...
Yeah I guess it actually is that easy now that you put it that way 😂 nothing to really regret purchasing or doing
danford.lau said:
Might be only person I’ve ever heard say 4.88 with 37s is over geared . It’s what I run and while it’s fine .. certainly not over geared



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Click to expand...
Iv talked to a lot of guys on here and they all seem to agree with you lol. I don’t know if it’s just because I’m in indiana and it’s ALOT of highway miles to get anywhere fun to explore or what, but I gained like 2mpg just switching from 37s to 38s. No way in hell I’d go back to a 37 on these gears if I ever had to travel long distance again.
 
danford.lau said:
Might be only person I’ve ever heard say 4.88 with 37s is over geared . It’s what I run and while it’s fine .. certainly not over geared



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Click to expand...
Haha that was exactly my thought running 4.88s and 37s. Shoot I even have a Rubi 4:1 tcase and I wish I had 5.13s

Honestly OP I agree with above if you think your 4.88s and 38s works then try it with the 40s....why not worst comes to worst it will be a little gutless but it will still drive.

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I personally love 5.38s and 37s. The 3.6 loves high rpms and runs hotter then most engines.


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I ran 5:13s on 37s and didn’t have any issues or feel like it was over geared at all. I’m currently running 40s on the same 5:13s and they work great with the 40s. I still chirp the tires every once in awhile when I have to pull out faster then normal. And I am still on my stock Dana 44s. I don’t wheel that often or that hard when I do. I think you would be happier with 5:13s on 40s. Just my two cents.


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Braxtonsag said:
Do you think my jeep only weighing 4500 lbs would have anything to do with me being perfectly fine with 4.88s and 38s?
Click to expand...


More than likely yes, But the 40's would be unsprung weight that has nothing to do with the overall weight of the vehicle. That additional rotational mass is what will make it a slug IMHO.
 
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I would be one of those people who would say that 5.38 is the right ratio to be running with 40's but I'd also be one to say that it's a terrible ratio to run on a Dana 44, especially if you're dead set on running 40's. The pinion on it is simply way too small. 5.13 is as high as I would go but being that you already have 4.88's and seem convinced it'll be fine, I'd just go with it.
 
jdofmemi said:
It's all good until "chirp" turns into "grind"[emoji24]
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So true man! It’s rare since I drive like a grandpa but it has happened a few times and I’m always relieved is a chirp and not a grind. It’s only a matter of time till it turns into a grinding noise.


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