Upgrade Choice: Axle Gear Ratio or Transfrer case?
JK Enthusiast
Joined: Sep 2007
Posts: 406
Likes: 0
From: Arkansas
Wolfman, if you are wanting scientific analysis, then you have to be very specific. An analysis is useless without all variables detailed and defined.
You keep comparing a 32" Sahara tire to a "35" tire as if all tires are created equal. That is absolutely pointless since there are 33" tires that weigh more than some 35" tires depending on what model of tire you are comparing. Also are these true measurements? Reason being that the "sahara tires" that came on my Sahara did not have a true 32" diameter. You must figure in your variables to get real world analysis. IE: make of tire, width, contact patch, and weight which is a HUGE factor. I can guarantee you along with everyone else on here that a 35" tire on 3.21 gears will be sluggish. IMO 4.10 gears with 35's are pretty sluggish. Especially if you are running heavy 10 ply mud tires.
On your priority list of upgrades, the transfer case should be at the bottom. You first need to worry about upgrading axle gears and figuring out what tire/ratio will be the best. For 35" tires the ideal is 5.13. This has been documented on this site a million times. Wheel with it how it is in order to determine what your next upgrades are going to be. I wouldn't worry about the Tcase until you have upgraded virtually everything under the Jeep. JMO
You keep comparing a 32" Sahara tire to a "35" tire as if all tires are created equal. That is absolutely pointless since there are 33" tires that weigh more than some 35" tires depending on what model of tire you are comparing. Also are these true measurements? Reason being that the "sahara tires" that came on my Sahara did not have a true 32" diameter. You must figure in your variables to get real world analysis. IE: make of tire, width, contact patch, and weight which is a HUGE factor. I can guarantee you along with everyone else on here that a 35" tire on 3.21 gears will be sluggish. IMO 4.10 gears with 35's are pretty sluggish. Especially if you are running heavy 10 ply mud tires.
On your priority list of upgrades, the transfer case should be at the bottom. You first need to worry about upgrading axle gears and figuring out what tire/ratio will be the best. For 35" tires the ideal is 5.13. This has been documented on this site a million times. Wheel with it how it is in order to determine what your next upgrades are going to be. I wouldn't worry about the Tcase until you have upgraded virtually everything under the Jeep. JMO
Thread Starter
JK Enthusiast
Joined: Aug 2009
Posts: 286
Likes: 0
From: Naples,Florida
Wolfman, if you are wanting scientific analysis, then you have to be very specific. An analysis is useless without all variables detailed and defined.
You keep comparing a 32" Sahara tire to a "35" tire as if all tires are created equal. That is absolutely pointless since there are 33" tires that weigh more than some 35" tires depending on what model of tire you are comparing. Also are these true measurements? Reason being that the "sahara tires" that came on my Sahara did not have a true 32" diameter. You must figure in your variables to get real world analysis. IE: make of tire, width, contact patch, and weight which is a HUGE factor. I can guarantee you along with everyone else on here that a 35" tire on 3.21 gears will be sluggish. IMO 4.10 gears with 35's are pretty sluggish. Especially if you are running heavy 10 ply mud tires.
On your priority list of upgrades, the transfer case should be at the bottom. You first need to worry about upgrading axle gears and figuring out what tire/ratio will be the best. For 35" tires the ideal is 5.13. This has been documented on this site a million times. Wheel with it how it is in order to determine what your next upgrades are going to be. I wouldn't worry about the Tcase until you have upgraded virtually everything under the Jeep. JMO
You keep comparing a 32" Sahara tire to a "35" tire as if all tires are created equal. That is absolutely pointless since there are 33" tires that weigh more than some 35" tires depending on what model of tire you are comparing. Also are these true measurements? Reason being that the "sahara tires" that came on my Sahara did not have a true 32" diameter. You must figure in your variables to get real world analysis. IE: make of tire, width, contact patch, and weight which is a HUGE factor. I can guarantee you along with everyone else on here that a 35" tire on 3.21 gears will be sluggish. IMO 4.10 gears with 35's are pretty sluggish. Especially if you are running heavy 10 ply mud tires.
On your priority list of upgrades, the transfer case should be at the bottom. You first need to worry about upgrading axle gears and figuring out what tire/ratio will be the best. For 35" tires the ideal is 5.13. This has been documented on this site a million times. Wheel with it how it is in order to determine what your next upgrades are going to be. I wouldn't worry about the Tcase until you have upgraded virtually everything under the Jeep. JMO
Thanks for your explanation. As I said in my previous post, I was just trying
to find scientific proof about the gear ration importance. I compared
two cases
3.73 stock gear ratio with 35 inch tire (my plan)
3.21 stock gear ration with 32 inch stock tire (stock sahara)
for this comparision, I assumed everything else is the same, including
tire weight and wind resistance etc.
Anyway, you pointed out the weight and actual size, which is very
valid "SCIENTIFIC PROOF" to me.
By the way, I have decided to upgrade my gear ratio to 4.88 and 35 inch tire
to get a better MPG than 5.13 and I guess it should be still adequate for medium
level offroad
JK Enthusiast
Joined: Sep 2007
Posts: 406
Likes: 0
From: Arkansas
Thats another variable in itself. Like other's have stated what you are doing with the Jeep is going to be the ultimate factor. Is it a daily driver that hits the freeway at 70+ or an off road rig; or is it something in between. I'm curious as to which tire you are going with. An A/T should be fine with 4.88's. My Sahara came with 4.10's and I'm currently running 33" Mud Grapplers. I am going to upgrade to 35's but go with a lighter A/T so I'm still trying to decide on 4.88's or 5.13's. Mine sees the pavement too so totally understandable about the MPG. Let us know the results when you get it done. Good luck
Last edited by BLACKSTONE; Oct 15, 2009 at 01:50 PM.
JK Enthusiast
Joined: Sep 2008
Posts: 231
Likes: 0
From: Phoenix, AZ
Thanks RedneckJeep:
Are you talking about Rubicon's transfer case that offer 4.1 ratio?
Then I agree it is not quite different from X/Sahara's transfer case that offer 2.72 ratio.
But I am talking about Atlas 4Speed transfer case that can offer up to 10.0
ratio.
To me, keeping the stock 3.73 gear axle ratio plus this new Atlas transfer case,
it gives good on street MPG (due to the stock 3.73 stock axle ratio) and great
offroad performance (maximum 10.0 transfer case ratio or selected 2.0, 6.0 transfer case ratio).
The reason that I am more for transfer case swap is because gear ratio
upgrade (without upgrade axle itself) is weakening the axle due to smaller
teeth of pinion/ring gear.
By the way, I agee with you about locker change too.
I believe adding a locker to the current differential or upgrade differential with a locker differential is easier than upgrading gear ratio. Am I correct or wrong on this?
Are you talking about Rubicon's transfer case that offer 4.1 ratio?
Then I agree it is not quite different from X/Sahara's transfer case that offer 2.72 ratio.
But I am talking about Atlas 4Speed transfer case that can offer up to 10.0
ratio.
To me, keeping the stock 3.73 gear axle ratio plus this new Atlas transfer case,
it gives good on street MPG (due to the stock 3.73 stock axle ratio) and great
offroad performance (maximum 10.0 transfer case ratio or selected 2.0, 6.0 transfer case ratio).
The reason that I am more for transfer case swap is because gear ratio
upgrade (without upgrade axle itself) is weakening the axle due to smaller
teeth of pinion/ring gear.
By the way, I agee with you about locker change too.
I believe adding a locker to the current differential or upgrade differential with a locker differential is easier than upgrading gear ratio. Am I correct or wrong on this?
But next, have you looked into the RubiCrawler from Advance Adapters? That thing is awesome, assuming you have an automatic. Then, IMO, you would not have to go as low in the axles, but I think you would still want them first.
JK Newbie
Joined: Mar 2008
Posts: 45
Likes: 0
From: Tampa, FL
Rockindoc:
Thanks for your response. It seems all people here simply says 3.73 sucks with 35 inch tire. But can you give me a scientific analysis on why it sucks?
The reason is still the same, if stock sahar comes with 3.2 and 32 inch tire, how
bad can 3.73 with 35 inch be?
Thanks for your response. It seems all people here simply says 3.73 sucks with 35 inch tire. But can you give me a scientific analysis on why it sucks?
The reason is still the same, if stock sahar comes with 3.2 and 32 inch tire, how
bad can 3.73 with 35 inch be?
JK Freak
Joined: Oct 2008
Posts: 896
Likes: 0
From: Colorado Springs, CO
JK Enthusiast
Joined: Feb 2009
Posts: 155
Likes: 0
From: Mechanicsville, MD
Yes, adding a locker without a gear change is less challenging. Since the pinion gear does not need to be removed, you are basically leaving gear settings alone. Except of course for ring gear backlash, which is relatively easy to get back into spec. All you need to do is simply replace any spacers in the order and side from where they came.
I've actually had no experience with the Atlas unit.....however, I have had extensive experience with gear changes and 4X4 drivetrains. It's "MY" personal experience that not much will compensate for better final drive gearing. I may be totally off base, but I think I am right on this.
Take the transfer case out of the equation for a minute. What do you have? An underpowered, incorrectly geared Jeep from the factory. These things make their best power starting around 2500 and going UP. They needed more final drive gear to begin with. You can throw the best transfer case at it in the world, and you're still under geared on the road. Why not do both? Then you'll have the best of both worlds.
Somebody feel free to correct me if I'm wrong on any of these points.
I've actually had no experience with the Atlas unit.....however, I have had extensive experience with gear changes and 4X4 drivetrains. It's "MY" personal experience that not much will compensate for better final drive gearing. I may be totally off base, but I think I am right on this.
Take the transfer case out of the equation for a minute. What do you have? An underpowered, incorrectly geared Jeep from the factory. These things make their best power starting around 2500 and going UP. They needed more final drive gear to begin with. You can throw the best transfer case at it in the world, and you're still under geared on the road. Why not do both? Then you'll have the best of both worlds.
Somebody feel free to correct me if I'm wrong on any of these points.
http://home.comcast.net/~kingslea1/Jeep/Gearing.pdf
JK Newbie
Joined: Mar 2008
Posts: 45
Likes: 0
From: Tampa, FL
So I'm going to order some 4.88s from Northridge because their price is amazing and install them with my dad who was a mechanic when he was younger. I have 26,xxx miles on my JK, do I need the overhaul kit or just the install kit? Methinks just the install kit, no?
JK Enthusiast
Joined: Nov 2011
Posts: 282
Likes: 0
From: Jersey Shore
Now my question is with an automatic transmission and 3.25" lift, 35" tires, dana 44 and 3.73 gears my experience is it handled amazing off road in mud/sand. My 2011 jk 4d is set up this way. Problem is not wheeling its highway driving. Here in jersey our roads are 65mph and most do 75-80(like myself) but the issue is to stay cruising at those speeds or even 70 its rpms are at about 3-3200. With getting 11.9 MPG or less. I would like advice on gearing and performance with the BEST MPG . Its seems everyone talks about manual not automatic. And remember the 2011 has the 3.8 not the mercedes 3.7L.
I might make this a new thread to help anyone else with the same question.
I might make this a new thread to help anyone else with the same question.