Upgrade Choice: Axle Gear Ratio or Transfrer case?
Thread Starter
JK Enthusiast
Joined: Aug 2009
Posts: 286
Likes: 0
From: Naples,Florida
Let's see, this is running a 6 speed.
My current setup:
Running 3.73 with 2.72 TC and 31.2s (stock tires)
Crawl ratio about 45.08:1
Idle at 750 in 4lo = 136 fps
65 mph = 2193 RPM
Running 4.88 with 2.72 TC and 35s
Crawl ratio about 58.98:1
Idle at 750 in 4lo = 117 fps
65 mph = 2558 RPM
Running 3.73 with 4.01 TC and 35s
Crawl ration about 66.71:1
Idle at 750 in 4lo = 103 fps
65 mph = 1955 RPM
Running 3.21 with 2.72 TC and 31.2s (stock size)
Crawl ratio about 38.80
Idle at 750 in 4lo = 158 fps
65 mph = 1887
Going with a Rubi TC or Atlas will give you better off road but the minor advantage on the road with your 3.73s compared to the 3.21 gearing is no where near enough to make up for the torque needed to turn 35s with their weight, volume and wind resistance. You will also be lifted which makes you more of a brick. Wind under the Jeep adds a good bit more resistance. Looking at what you want, running 35s with 3.73 gearing compared to 3.21 gearing with stock tires gives you about 68 RPM advantage at 65 mph. Do you thing the Jeep is going to build up much more torque with that little gain to turn those tires?
I would hate to have worse performance than my stock setup.
My current setup:
Running 3.73 with 2.72 TC and 31.2s (stock tires)
Crawl ratio about 45.08:1
Idle at 750 in 4lo = 136 fps
65 mph = 2193 RPM
Running 4.88 with 2.72 TC and 35s
Crawl ratio about 58.98:1
Idle at 750 in 4lo = 117 fps
65 mph = 2558 RPM
Running 3.73 with 4.01 TC and 35s
Crawl ration about 66.71:1
Idle at 750 in 4lo = 103 fps
65 mph = 1955 RPM
Running 3.21 with 2.72 TC and 31.2s (stock size)
Crawl ratio about 38.80
Idle at 750 in 4lo = 158 fps
65 mph = 1887
Going with a Rubi TC or Atlas will give you better off road but the minor advantage on the road with your 3.73s compared to the 3.21 gearing is no where near enough to make up for the torque needed to turn 35s with their weight, volume and wind resistance. You will also be lifted which makes you more of a brick. Wind under the Jeep adds a good bit more resistance. Looking at what you want, running 35s with 3.73 gearing compared to 3.21 gearing with stock tires gives you about 68 RPM advantage at 65 mph. Do you thing the Jeep is going to build up much more torque with that little gain to turn those tires?
I would hate to have worse performance than my stock setup.
woffles:
Thank you so much for this post.
Therefore, what you said is 3.73 with 35 inch tire is a little bit better
than one stock setting (3.21 and 31 inch tire). But this is a big drop
from 3.73 with 31 inch stock tire. So it still better to upgrade to 4.88
Also, I noticed you brought one more scientific proof, the lifted
jeep will meet more wind resistance.
Thanks!
Thread Starter
JK Enthusiast
Joined: Aug 2009
Posts: 286
Likes: 0
From: Naples,Florida
which gear ratio is most verstatile
OK, I am pursuaded by all the facts and scientific analysis that I will
opt for axle gear ratio upgrade first.
Currently, with my stock 3.73 axle ratio and stock tire P225 75 R16 (i.e. 30 inch
tire), the rpm is about 2200 at 70mph/6th gear.
My goal is change tire to 35 inch. So I am facing a choice of 3 gear ratio
which will raise my cruise rpm to
4.56 2305
4.88 2466
5.13 2593
Which is do you recommend to be the all-around winner?
opt for axle gear ratio upgrade first.
Currently, with my stock 3.73 axle ratio and stock tire P225 75 R16 (i.e. 30 inch
tire), the rpm is about 2200 at 70mph/6th gear.
My goal is change tire to 35 inch. So I am facing a choice of 3 gear ratio
which will raise my cruise rpm to
4.56 2305
4.88 2466
5.13 2593
Which is do you recommend to be the all-around winner?
Last edited by wolfmanii; Oct 6, 2009 at 05:33 AM.
JK Enthusiast
Joined: Jan 2009
Posts: 414
Likes: 0
From: Charlotte, NC
All around winner would be 5.13's from what everyone says. Thats what I will be going to. For a 288 rpm difference at 70mph, you might as well get the lowest gear you can to give you better acceleration. Also, it will help you actually stay in 6th gear on the highway instead of having to downshift to go up a small hill.
Thread Starter
JK Enthusiast
Joined: Aug 2009
Posts: 286
Likes: 0
From: Naples,Florida
can gear upgrade be done while keepin the current tire?
can gear upgrade be done while keepin the current
tire size? If so, do I have to use 2nd gear to start?
Since it is good time to add locker while upgrading gear, what locker should I choose.
I see 3 types
electric (Eaton)
air (ARB)
mechanical (ox trax locker)
From what I heard, air locker is the most reliable one.
Why is it? is it because electic locker is more vulnerable to water?
My first impression is electric locker is better since
air locker need to run long air hose between compressor
to the front and rear axle and maybe it will cause more
trouble than a simple electric wire used by electric locker.
Also, how about the all mechanical locker. If it does not use air compressor or electric power, maybe it is more reliable?
If you have a choice between free limited-slip differential and on demand complete locker, I guess
you prefer the true complete locker, right?
tire size? If so, do I have to use 2nd gear to start?
Since it is good time to add locker while upgrading gear, what locker should I choose.
I see 3 types
electric (Eaton)
air (ARB)
mechanical (ox trax locker)
From what I heard, air locker is the most reliable one.
Why is it? is it because electic locker is more vulnerable to water?
My first impression is electric locker is better since
air locker need to run long air hose between compressor
to the front and rear axle and maybe it will cause more
trouble than a simple electric wire used by electric locker.
Also, how about the all mechanical locker. If it does not use air compressor or electric power, maybe it is more reliable?
If you have a choice between free limited-slip differential and on demand complete locker, I guess
you prefer the true complete locker, right?
Thread Starter
JK Enthusiast
Joined: Aug 2009
Posts: 286
Likes: 0
From: Naples,Florida
All around winner would be 5.13's from what everyone says. Thats what I will be going to. For a 288 rpm difference at 70mph, you might as well get the lowest gear you can to give you better acceleration. Also, it will help you actually stay in 6th gear on the highway instead of having to downshift to go up a small hill.
But don't you think 5.13 will make the axle weaker? This is because
lower gear causes smaller pinion size and teeth.
JK Enthusiast
Joined: Jan 2009
Posts: 414
Likes: 0
From: Charlotte, NC
Dont worry about breaking the axle due to the gear change. If you dont drive like an idiot or do heavy rock crawling, no need to worry. There are people who run 37's on the stock D30 and have had no problems. Go easy on the gas and choose your lines well and you wont break anything with 5.13's and 35's. It all depends on how you drive.
JK Super Freak
Joined: Feb 2007
Posts: 1,416
Likes: 0
From: Dallas, Texas
wolfman... if you have a stick, the ring and gear upgrade is much less significant than it is in an automatic. Let me expand on this. If I am driving in 5th gear doing 70mph running at 2850 rpms... how is that any different then running 4:88s running in 6th gear doing 70mph at 2800 rpms. The fact is there is no real difference (expect you now of a 5-speed with a weak overdrive). Granted you get a little more pep on acceleration, but the stick has a lower gear ratio in 1st and 2nd gear and will have enough pep.
If it were my dime... I would get the atlas because you will have more controllability on the rocks with the higher gear ratio. The problem with a stick is that you have to commit when crawling so the higher the crawl ratio, the better off you are... to a point. Not sure if all you need is 6:1 vs the 10:1 that you are looking at.
If it were my dime... I would get the atlas because you will have more controllability on the rocks with the higher gear ratio. The problem with a stick is that you have to commit when crawling so the higher the crawl ratio, the better off you are... to a point. Not sure if all you need is 6:1 vs the 10:1 that you are looking at.
JK Super Freak
Joined: Apr 2009
Posts: 1,633
Likes: 0
From: Forsyth County, GA
My JK is quite peppy with the Manual tranny, 3.21 gears and the SRA's ... but it was definitely a dog with the same setup and KM's ..... definitely a tire weight issue.