View Full Version : Axle Ratios

August 29th, 2006, 04:52 PM
Right now I am in process of updating my 4 cyl. YJ to 8.8 rear and D44 front.

Other then a few trips to Silver Lake all my wheeling has been in the St.Helen area.

Here are the details.

4cly./manual trans for now. A SBC/4500/Atlas in the new year.

33x13.50 tires. Someday 35/7/8`s

Asking for some advice on ratio selection. Simply because I am not familar with say Drummond Island, or Gitchee Gummee etc.

Do I want a low 5.13 or perhaps a 4.88 or ??? Again based on some of the other areas within the State the grpup wheels in.


August 29th, 2006, 06:25 PM
I'm no expert but with a SBC and an atlas you would be fine for most things with 4:11's rolling on 35's. It really depends on how you want your axle ratio to effect other areas of driving. I mean driving down the highway with ultra low gears will put the rpm up higher and you lose fuel economy...but off road the lower gears are nice. I know I wish I had a 4th gear to get into on my SBC and th350 automatic in my YJ when I am on the road.

Some say the lower the better but most of us have to keep some kind of streetability. That's why 4:1 conversions and atlas t-cases are so nice. You can keep a little higher gear, but still have a deeper low to hop into when you need it. Sometimes wheel speed is your friend...depends on what you are going for. Rock...lower is better, gives you far more control....deep sticky mud and you might really want the tires going. I have seen super buggies that are built for crawling just get burried in the mud because the wheels don't spin enough to clean out, and I have seen mud built rigs that don't have enough on the low end to turn the tires slow enough to offer control on the rocks and they smash and bash their way around going far too fast for the rocks.

So basicly...I can't help after typing all this... :ahhh:

August 29th, 2006, 08:13 PM
You see my dilema. A basic question but one that seems to be hard to answer.
Michigan offers such a wide range of trails. WOT Silver Lake/Deep Mud to what I think would be rock type crawling @ Drummond.

The YJ will spend most of it`s time by far off road. Fuel economy only becomes an issue when you run out......

So do you harness a SBC with a bunch of gear and let it spin or lug it down with a tall gear when it comes to the crawley stuff ?

Right now with the 4 cyl. all the gear I can get is about the best answer. As it has a limted amount of power to begin with.

August 29th, 2006, 09:57 PM
I think with the SBC, Atlas and 35's, 4.11's would be a good all round wheeler with an auto, but with a manual you might wanna go just a bit deeper. If you need super low, use the atlas to get it. Otherwise let the tires get some speed without having to change gears too many times. I'll be swapping gears this winter and i'll be going to 4:11's with my SBC, TH350, NP231 (or a Dana 300 if I get round to it) and 35 inch tires.

August 29th, 2006, 10:19 PM
Thanks for the feedback. Thinking I am going to set it up with 4.88`s and do the atlas with a lower(est) low range.

While it may be overgeared with just 33`s. A move up to a talller tire ought to bring the overall gearing "in the ball park"
without having to regear the axles.

Keeping in mind the overall gear ratio`s in a A(x?) 15 it has in it now and the slightly lower gearing of the Atlas.

Have spent some time figuring speed vs. RPM vs. ratio on the following table.

http://members.shaw.ca/snowjeep/tirecalc.htm A useful table.

August 29th, 2006, 10:34 PM
I run 5.13s in both of my rigs, a 1993 Jimmy and a 1990 Samurai. One has 36's and the other has 33's. I love the ratio, escpecially since I have an overdrive in both (NV4500 in the jimmy)

Renegade II
August 29th, 2006, 10:39 PM
My $.02

I like the 4:88 gears in my old Jeep. Trail, road, mud, rock or sand they work well and keep the mechanical leverage at the end of the powertrain, thus reducing stress up the line. But..........

With A well built V8 I wouldn't go with more than 4:56's in a Dana 44 or you could end up breaking ring gear teeth if you have a heavy right foot. That happened to me a couple times on my CJ8, I backed it off to 4:56's and never had another problem with it. When you get to 4:88 and beyond with a Dana 44 those ring gear teeth grow in number but shrink in size and strength.

Just a past experience I thought I'd share, good luck with the build. :D

August 30th, 2006, 09:13 AM
I have a SBC, Turbo 350 and a 231 transfer case which is 2.7:1 or 2.9:1 or close. (not sure) I currently have 4.56 gears and feel it works quite well. If you are doing a lot of Silver Lake running (which I do) the lower gears in the Atlas will make you run out of gear quickly if you go lower in ratio. I am running 33" paddle tires and at times will redline around 6000-6500.

If you are running 35" tires with the 4:1 ratio, you will be close to the same or possibly worse. I could go thru the numbers but am currently at work.

As far as crawling goes, I find that I am never in need of more power. The torque & hp along with the automatic has never been a problem. I am also running 35" tires while off road. The only time I wish for lower gears is while crawling down hill. I ride the brake more than I would like and wish I had better compression braking. You will be a little better with the atlas.

You really need to determine if you want a terrain specific vehicle or an all around wheeler. If you want an all around wheeler, go with 4.56. If you want a dedicated crawler, go lower to something like a 5.13.

Just my thoughts.


August 30th, 2006, 09:22 AM
id go real low if i didnt street it much! you can run hi range 1st gear in the mud or sand for wheel speed. but if your gonna drive it on the street that changes everything. with 33's and a 4 cylinder id say 4.88 or 4.56 if it sees any street action. perhaps go 4.88 and it would be middle of the road area for now and still be adequate for sbc nv4500 swap later
good luck

August 30th, 2006, 10:58 AM
You can run hi range while in the open dunes. But it is still great to grab a low gear for playing around in the badlands area of the dunes. Depends on how you like to drive. Personally, I like to idle up to the bottom of the hills and then be able to hammer it. In some cases, high range doesn't work.

I have run a variety of tire type and size at the dunes over the past 30 years. For the most fun, you want both high and low range to be effective.

August 30th, 2006, 09:36 PM
<div class='quotetop'>QUOTE(WhiteRhino &#064; Aug 30 2006, 09&#58;13 AM) 17035</div>

If you are doing a lot of Silver Lake running (which I do) the lower gears in the Atlas will make you run out of gear quickly if you go lower in ratio.


You really need to determine if you want a terrain specific vehicle or an all around wheeler. If you want an all around wheeler, go with 4.56. If you want a dedicated crawler, go lower to something like a 5.13.

Just my thoughts.


I agree with with what jim said.I found out that my 3.8 atlas and 5.13&#39;s in low range at the dunes was just to low. 1st gear in high works good and gets me up the dunes fine.I only get out there maybe 1 time a year so its not a big deal to me. as for crawlin though ,I love the control the atlas gives you, especialy on the down hill stuff and climbing over stuff.

August 31st, 2006, 06:47 AM
I approached the gearing in mine from a stress direction. I wanted to avoid large stress loads on the drive shafts, differential, and T-case side of things, my thinking that the axles should survive longer when they don&#39;t work as hard. Then I had to balance in the size/strength of the pinion depending on which gearing I chose. I had planned on 4.56 when I first started, but decided to go one step deeper and did the 5.13&#39;s.

I guess I&#39;ve been lucky so far, I haven&#39;t destroyed my Rubicon Express Cut and Tap SYE, been running that for about 4 years now and about 2yrs on 36&#39;s. But with your setup, Atlas, SBC, Auto, I&#39;d say your driveline should take quite alot considering the weight of your Jeep. The low range Atlas takes the abuse instead of your trans, and the Atlas should hold up to anything&#33; So, it now goes to your axles.

So, with all that, I think your best ratio would be 4.56 for a stick and 4.11 for an auto....Someone smarter than me posted somewhere to step one ratio down with an Automatic trans than with a Manual.

But, my solution to the Dunes, Crawling thing is to stack boxes....thats what I&#39;m working on now, so you get all your stock ratios but also get a really low gear for goin&#39; slow (231/D300) or 2 speed Atlas&#33;


August 31st, 2006, 08:21 PM
Thanks for the help folks.

Decided to run 4.88&#96;s.

5.13&#96;s and even 5.38&#96;s looked good but after running the numbers of different speeds, tire size and ratio(s). The best compromise would be 4.88&#96;s for the more "open&#39;" areas of the state. The almost 6.0 1st gear of the NV4500 and the Atlas lows would (should) work for the creepy crawly stuff.

Still though 5.13 does sound nice........ :confused:

See ya on the trail &#33;&#33;