Jersey Joe

Sorry guys . . . hope these aren't "stupid" questions . . .


I'm a newbie Jeep owner . . . love my 2012 stock Sahara!

It has a 3.21 rear axle ratio. I am not an engineer, but I can understand some concepts! When the time comes, if I wanted to upgrade to larger tires (say 35"), I would need to increase the rear axle ratio to "deeper" (numerically higher) gears, right? Maybe a 3.73 gear?

I have been reading Jim Allen's book, etc. but I'm still learning, etc. and am confused. Sorry.



Questions:

1) If you change your rear axle ratio to a numerically higher gear (as I had done with my 1998 Mustang from 2.83 to 3.27) you should improve the acceleration. With heavier and larger tires, an increase in gearing should compensate for the increased mass of the tires and keep strain off the drivetrain, right?

So . . . wouldn't you also have to change the front axle ratio to match the rear? Or did I misunderstand something?



2) My Jeep has a "Dana 44" rear axle and a "Dana 30" front axle. I know that the Rubicons have both front and rear Dana 44's. Can someone please explain the differences . . . what does the "44" and "30" mean? Is it the number of splines on each axle? I would assume that a Dana 44 is a heavier and stronger axle of course, if they put it on the Rubicon.


I tried to figure these things out on my own, but with no luck.


As a newbie, I am getting more and more interested in the technical aspects of our Jeeps, but . . . I am not the sharpest knife in the drawer, nor am I very mechanically inclined (at this point anyway).

Thanks so much for any explanations or any links you could provide!


You folks are really great!



All best, and Merry Christmas,
Joe

Cold

I think we live in the same knife drawer but I'll see if I can help you out a bit.

Both differentials need to be geared the same for them to work together. If they were different then the front and rear tires would turn at different rates in 4 wheel drive mode. That be very bad.

I "think" that the main reason people change gears ratios is due to getting larger tires. The larger tires make the engine work harder due to the larger diameter changing the "Final drive ratio". You regear to regain lost power. This would basically shift the load to the axles.

I personally am not sure what the 30 and 44 mean on a Dana but I can tell you that the 44 can handle bigger gears. I think the tubes are basically the same.


I hope that helps. Im sure someone smarter then me will chime in to help you out

thedrod

A lot of these questions are answered on here already in the Newbie FAQ section.

Adding taller tires to your jeep effectively raises your gear ratio. Changing to a lower gear (higher numerically) corrects the ratio for the increased diameter of the wheels.

Yes you have to change both front and rear gear sets.

The Dana 44 is a "beefier" and slightly bigger setup than a 30. The 30 can only take gears up 5.xx something.


EDIT:

Here is a copy and paste I found on a website.

The manufacturer of the vehicle designed it (with stock differential gearing and stock tires) to operate most of the time within this efficient and ideal power band. The issue is that many off road modifications effectively “raise” the gearing of your Rover. One of the most common and best understood but certainly not the only modification that effectively raises the overall gearing is taller tires. Think of the earlier example we used, a 3.54 differential gear will still rotate the tires once for every 3.54 times the engine goes around but the taller tire will roll a longer distance. So at the same engine speed, your miles per hour or road speed will go up, hence to maintain, say the legal speed limit, you need to drop the engine speed. This is where the gearing problem starts. When you drop your engine speed below 2300/2400 rpm, you exit the power band and start suffering the consequences of it.


Here are some links

https://www.jk-forum.com/forums/show...276#post211276

http://gbrutah.com/introdiffgearing.html

http://en.wikipedia.org/wiki/Dana_30

http://en.wikipedia.org/wiki/Dana_44

Jersey Joe

Thanks for your responses, guys . . .


Sorry, I missed the post with the FAQ's . . . I'll check out those links as well!

I know it's annoying when newbies ask the same questions over and over.


All best, and thanks again,
Joe

thedrod

No worries! It's always a good discussion