Atlas 4-speed gearing

mrblaine said:

You know what folks with autos never discuss? That's right, crawl ratio. The auto is far too forgiving and easy to control for that number to even begin to matter. I have never known or cared to know the crawl ratio of a single axle, tire, and gear combo I've had in any of my rigs over the years.

Your ideal world in nowhere near the same planet as mine. I have zero use for 10.88-1 unless someone has given me the task to see how much of their stuff I can break. Then that is a very useful ratio with the auto. The chassis won't even torque over much when you blow up a rear axle.

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I don't care about the 10.88:1. I just think having the 2.72:1 in addition to the 4:1 would be helpful in snow and mud. I'll know much better after just wheeling with the auto and 4:1, and my hope is no more changes to the ratios will be needed. Everything is packaged nicely right now. Minimalist build sufficiency. I learned that from someone really smart on here.

JMT said:

I'm glad this thread is happening because with the auto swap underway and the 4:1 Tera-4 Low I'm not sure what wheeling will be like. My crawl ratio is going from 82:1 to something like 53:1. I'm not too worried about it due to the T/C, but I was already looking at my gearing with a Rubicrawler, but due to the weakness of the Tera 4-Low I'd have to remove it and go with a 231. That would make my ratios 1:1, 2.72:1 and 7.44:1. Nothing in the 3.8-5.5 range. All I'd be getting for $2000 is 7.44:1. Seems like a large waste of money. I concluded it's best to wait and see how it wheels with the auto.

My ideal world is a 241 with a Rubicrawler. Just need to shell out another $4500.

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Wait until you drive the Auto...you will change your Ideal.

mrblaine said:

You know what folks with autos never discuss? That's right, crawl ratio. The auto is far too forgiving and easy to control for that number to even begin to matter. I have never known or cared to know the crawl ratio of a single axle, tire, and gear combo I've had in any of my rigs over the years.

Your ideal world in nowhere near the same planet as mine. I have zero use for 10.88-1 unless someone has given me the task to see how much of their stuff I can break. Then that is a very useful ratio with the auto. The chassis won't even torque over much when you blow up a rear axle.

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To put that in perspective, if I dropped that 10.88:1 in my rig I would be throwing over 100,000 foot pounds at the axle shafts.

That's what Blaine means about breaking stuff.

NashvilleTJ said:

To put that in perspective, if I dropped that 10.88:1 in my rig I would be throwing over 100,000 foot pounds at the axle shafts.

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Only with enough resistance.

NashvilleTJ said:

That's what Blaine means about breaking stuff.

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Yep, stupid easy to do when you are used to the chassis and motor bogging with a manual to tell you when to slam in the clutch. The auto just keeps building torque until the rig moves or something breaks and typically with gearing that low, the chassis doesn't react much.

HenikonLJ said:

You said you run the 2.0 case, what made you go that route over say a 3.0? I honestly play in the rocks a couple times a year. Otherwise I'm in the snow or sand. I see your point in your last post and an considering it. The 8.16 id get with the 2.72-3.0 seems like more options than the 3.8 or 4.3 would give me. Like I said before on the Toyota I hardly used double low unless I was showing off or in really crap snow trying to get back on top.

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He, like most of us, is after usable ratios. The 3.0 gives you 1-1, 2.72-1, 3.0-1, and 8.16-1. The middle two are too close together and your low is too far from the middle two.

HenikonLJ said:

You said you run the 2.0 case, what made you go that route over say a 3.0? I honestly play in the rocks a couple times a year. Otherwise I'm in the snow or sand. I see your point in your last post and an considering it. The 8.16 id get with the 2.72-3.0 seems like more options than the 3.8 or 4.3 would give me. Like I said before on the Toyota I hardly used double low unless I was showing off or in really crap snow trying to get back on top.

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As I said above, it was all about the resulting ratios. An 8.16:1 ratio in my rig would be absolutely useless. I spend the majority of my time on the trail in 2:0:1. It works for my rig.

HenikonLJ said:

I want to know what people have found works best in the jeep world with the 6 speed.

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In that case, I and many others have found 5.13 gearing works great with the 6spd and 35s. I run that setup with the rubi 4.0 TC. I never stall in 4hi and often start in 2nd gear. Makes 4hi very usable in mild offroad situations unlike your 4.10 gearing.

HenikonLJ said:

I will still be within 400rpm of what I will end up when I get the new axles under.. 410 and 35s is just as big of a gap as 538 and 40s.

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In theory, that's true but what it doesn't account for is the larger rolling mass that is both harder to get moving, and harder to stop moving.

I’ll give you my take on it as I have an Atlas 4 speed with an AX-15 five speed, 4.0L and 5.13 gearing in the axles.
I had a 4:1 terra low kit and had the same issue you described as I found low range was too low on a lot of trails to keep up and high range I just felt lacking for how steep the terrain was. So I purchased the Atlas 4 speed in a 3.8:1. I wound up with 1:1, 2.73:1, 3.8:1 10.34:1 ratios. I honestly thought the 10.34:1 would be useless and only for showing off or playing however it has proven to be very useful. I gained the 2.72:1 that I use on most trails, then I use the 3.8:1 in the rocks, and on the sketchy stuff I’ll occasionally use the doubler to really gain control. It is honestly perfect set up for me. I never want another Jeep without a four speed t case. I’ll be ordering one for my wife’s JL as well. Now for the downside. It adds length. If I was to do it over I’d have done the ultra short output even though I’d loose my speedometer. Just for the extra drive shaft length. I’m not sure how people are getting them in the Tj’s without a rear wheelbase stretch. I’m stretched almost six inches in the rear and with the standard type rear output that mantains the speedometer output my driveshaft is about as short as I can get away with having 12” travel shocks.