Gears and Tire size with Auto and 6 Speed - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > Models > Jeep Wrangler Forums > JK Wrangler Technical Forum > Gears and Tire size with Auto and 6 Speed

Engo winches available at www.rockridge4wd.com! Free shippThe Original 3/8" Ruffstuff Diff Cover!Ruffstuff 3 Link Kit!

Reply
Unread 07-23-2010, 01:59 PM   #1
MilitaryJK4455
Web Wheeler
2010 JK Wrangler 
 
Join Date: Mar 2009
Location: Ft. Detrick MD
Posts: 2,631
Gears and Tire size with Auto and 6 Speed

To potentially stop this current influx of threads about the same subject everyone tune in here... If any of this is wrong please discuss and prove me wrong...

You guys are not listening to what we are saying just by reading some of these responses.... 3.73's or 4.10's in a STANDARD 6 speed transmission is just fine... You will get around 15 in town and 17-20 interstate depending how you drive.... This is not applicable with the AUTOMATIC transmission... An auto with 3.73's or 4.10's is going to be a dog with bad gas mileage... check out this chart...



-An automatic with 35's would have to gear to 4.56's just to get to the performance of a standard tranny with 3.73's and 35's.
-An automatic with 35's would have to gear to 5.13's just to get to the performance of a standard tranny with 4.10's and 35's.
-An automatic with 35's would have to gear to 5.38's just to get to the performance of a standard tranny with 4.88's and 35's.

-A standard tranny with 35's and 3.21's is a dog...
-An auto tranny with 3.21's does not exist...
-A standard tranny with 35's and 3.73's is a doable set up (not a dog).
-An auto tranny with 35's and 3.73's is a dog...
-A standard tranny with 35's and 4.10's is a decent set up (lower end of stock performance)
-An auto tranny with 35's and 4.10's is a dog...
-A standard tranny with 35's and 4.56's is a good set up (higher end of stock performance)
-An auto tranny with 35's and 4.56's is a doable set up (not a dog)
-A standard tranny with 35's and 4.88's is an ideal set up (lower end of high performance set up)
-An auto tranny with 35's and 4.88's is a doable set up (close to stock)
-A standard tranny with 5.13's should be running 37's (getting to the highest end of high performance)
-An auto tranny with5.13's has just gotten to a stock set up (the lower end of stock)

Catch my drift?

Even some of these calculations are giving the auto the benefit of the doubt...

MilitaryJK4455 is offline   Reply With Quote
Unread 07-23-2010, 02:12 PM   #2
1398653
Registered User
2004 TJ Wrangler 
 
Join Date: Jan 2009
Location: Olean NY, New York
Posts: 1,060
I have 3.21 6 speed with 34 inch Goodyear MTRs which measure the same size as a lot of 35s out there. It is ok on the highway and around town, not great, I would describe it as livable and not that annoying. Off road it is a pain in the arse. It takes quite a bit of skill crawling rocks and keeping momentum going up steep hills. BUT it is doable. That being said I am regearing to 4.88s to get more off road performance. I just thuoght I would add some personal obervations involving 3.21s and 34-35s. a lot people make it sound like 3.21s with 35s will be like driving your jeep with square tires. It is not as bad as some make it out but is certainly isnt ideal. When I went on a jeep jamboree the guides kept asking me if I was in 4 wheel low. I had to explain it to several people that my gearing sucks.
__________________
Steve, Olean NY, 2004 TJ Rubicon & 2006 LJ Unlimited
1398653 is online now   Reply With Quote
Unread 07-23-2010, 02:13 PM   #3
Imped
Web Wheeler
 
Imped's Avatar
2004 TJ Wrangler 
 
Join Date: Feb 2008
Location: Indianapolis
Posts: 19,217
Nice thread. To add to it:

The 6 speed manual offered in JK's is the NSG370. It's a Mercedes-sourced unit that was also used in 05-06 TJ's.

Gear ratios:
1st - 4.46
2nd - 2.61
3rd - 1.72
4th - 1.25
5th - 1.00
6th - .84
Reverse - 4.06

The 4 speed auto used in the JK's is the 42rle. It was used in 03-06 TJ's as well.

Gear ratios:
1st - 2.84
2nd - 1.57
3rd - 1.00
4th - 0.69
Rev - 2.21

Now look a little deeper. The OD on the 42rle is 15% higher than the NSG370. So, for any given tire size, RPM's will be 15% lower. This is why the axle gearing needs are very different for the two transmissions. Just saying "you need 4.88 gears for 35" tires" doesn't do it. You're missing out on half the story. Axle gearing is simply a function of engine, transmission, and tire size. The NSG370 also makes use of a much lower first gear, which is awesome for crawling. Lastly, it has 2 more gears before OD, so the RPM drop between gears is reduced considerably compared to the 42rle, helping the engine stay in its powerband. Combine all of that and the numbers speak for themselves--4.10's and 35's are very liveable with the NSG and not even close with the 42rle. To give you the same performance as an equivalent JK with the NSG, you should gear ~20% deeper with the 42rle.
__________________
OlllllllO
Float Test Build
IndyORV

Last edited by Imped; 07-23-2010 at 02:54 PM..
Imped is offline   Reply With Quote
Unread 07-23-2010, 02:19 PM   #4
MilitaryJK4455
Web Wheeler
2010 JK Wrangler 
 
Join Date: Mar 2009
Location: Ft. Detrick MD
Posts: 2,631
Quote:
Originally Posted by Imped View Post
Nice thread. To add to it:

The 6 speed manual offered in JK's is the NSG370. It's a Mercedes-sourced unit that was also used in 05-06 TJ's.

Gear ratios:
1st - 4.46
2nd - 2.61
3rd - 1.72
4th - 1.25
5th - 1
6th - .84
Reverse - 4.06

The 4 speed auto used in the JK's is the 42rle. It was used in 03-06 TJ's as well.

Gear ratios:
1st - 2.84
2nd - 1.57
3rd - 1.00
4th - 0.69
Rev - 2.21
Thanks imped... That will do people some well in the future for the F.A.Q thread... You sure do know a lot about JK's... You sure you dont own one?
MilitaryJK4455 is offline   Reply With Quote
Unread 07-23-2010, 02:42 PM   #5
Imped
Web Wheeler
 
Imped's Avatar
2004 TJ Wrangler 
 
Join Date: Feb 2008
Location: Indianapolis
Posts: 19,217
Sure don't. The JK is still a Jeep with solid axles at both ends. Everything is transferrable. Having the same transmissions as TJ's doesn't hurt, though.
__________________
OlllllllO
Float Test Build
IndyORV
Imped is offline   Reply With Quote
Unread 07-23-2010, 02:46 PM   #6
MilitaryJK4455
Web Wheeler
2010 JK Wrangler 
 
Join Date: Mar 2009
Location: Ft. Detrick MD
Posts: 2,631
Quote:
Originally Posted by Imped View Post
Sure don't. The JK is still a Jeep with solid axles at both ends. Everything is transferrable. Having the same transmissions as TJ's doesn't hurt, though.
Yeah, I guess thats true...
MilitaryJK4455 is offline   Reply With Quote
Unread 07-23-2010, 02:53 PM   #7
Imped
Web Wheeler
 
Imped's Avatar
2004 TJ Wrangler 
 
Join Date: Feb 2008
Location: Indianapolis
Posts: 19,217
I'm an advocate for applied physics, geometry, and just going by the numbers. Numbers don't lie. It doesn't matter if we're talking about YJ's, TJ's, JK's, XJ's, etc. If you understand the fundamentals, those are just letters. Math and physics doesn't change. Your thread does a good job of explaining that. The problem is most people don't view things in black and white like that....the JK section especially.

PS, the gearing charts are excellent. I'm glad someone else got as fed up about gear threads as me.
__________________
OlllllllO
Float Test Build
IndyORV
Imped is offline   Reply With Quote
Unread 07-23-2010, 03:05 PM   #8
MilitaryJK4455
Web Wheeler
2010 JK Wrangler 
 
Join Date: Mar 2009
Location: Ft. Detrick MD
Posts: 2,631
Quote:
Originally Posted by Imped View Post
I'm an advocate for applied physics, geometry, and just going by the numbers. Numbers don't lie. It doesn't matter if we're talking about YJ's, TJ's, JK's, XJ's, etc. If you understand the fundamentals, those are just letters. Math and physics doesn't change. Your thread does a good job of explaining that. The problem is most people don't view things in black and white like that....the JK section especially.

PS, the gearing charts are excellent. I'm glad someone else got as fed up about gear threads as me.
Well, dont give me credit for the gear chart... I did not make it... I was actually confused for the longest time as a newb because all that I had ever seen for the JK was an auto chart so I thought that my Jeep with the 3.73's according to the chart was going to be a complete dog with the 35's on... Then I stumbled upon the standard tranny chart and realized that all would be fine and dandy
MilitaryJK4455 is offline   Reply With Quote
Unread 07-23-2010, 03:07 PM   #9
rballman
Registered User
2007 JK Wrangler 
 
Join Date: Oct 2007
Location: Durango, Colorado
Posts: 1,697
And here I was about to start another thread!!




JK
__________________
2007 Wrangler X - Jeep Green, 4" lift, 4.88s, locked rear, custom bumper/fender/cage, rolling on 35s w/ 15s

Colorado Jeep Club member #2007

My JK Build Thread
rballman is offline   Reply With Quote
Unread 07-23-2010, 03:10 PM   #10
MilitaryJK4455
Web Wheeler
2010 JK Wrangler 
 
Join Date: Mar 2009
Location: Ft. Detrick MD
Posts: 2,631
Quote:
Originally Posted by rballman View Post
And here I was about to start another thread!!




JK
Your a **** ball...
MilitaryJK4455 is offline   Reply With Quote
Unread 07-23-2010, 03:14 PM   #11
rballman
Registered User
2007 JK Wrangler 
 
Join Date: Oct 2007
Location: Durango, Colorado
Posts: 1,697
I plan on running 46s one day. Can you find a better chart that has my size on it??






...ok I will stop now. This is good information; nice work.
__________________
2007 Wrangler X - Jeep Green, 4" lift, 4.88s, locked rear, custom bumper/fender/cage, rolling on 35s w/ 15s

Colorado Jeep Club member #2007

My JK Build Thread
rballman is offline   Reply With Quote
Unread 07-23-2010, 03:17 PM   #12
MilitaryJK4455
Web Wheeler
2010 JK Wrangler 
 
Join Date: Mar 2009
Location: Ft. Detrick MD
Posts: 2,631
Quote:
Originally Posted by rballman View Post
I plan on running 46s one day. Can you find a better chart that has my size on it??






...ok I will stop now. This is good information; nice work.
Yeah... You'll need new axles and 5.86's... possibly 6.17's you **** miester
MilitaryJK4455 is offline   Reply With Quote
Unread 07-23-2010, 08:00 PM   #13
Farmdiesel
Registered User
2007 JK Wrangler 
 
Join Date: Apr 2010
Location: NC
Posts: 37
I think if that Tranny chart was a sticky it would help Military JK. When I 1st started looking at JKs I didn't understand the difference b/t the auto and the 6sp. Knowing the stock differences b/t transmissions is huge when you are picking gear and tire sizes. When I drove my 6sp with 4.10s home for the 1st time I was freaked out and thought I had made a big mistake until I did a little more research.
Farmdiesel is offline   Reply With Quote
Unread 07-23-2010, 08:40 PM   #14
MoparToYou
Registered User
2013 JK Wrangler 
 
Join Date: Sep 2008
Posts: 608
I would add another line at the bottom of your opening post for auto tranny with 5.38 gears. It is still only "acceptable" based on your chart, and I would agree with that. 5.38 gears are acceptable, but not great by any means. For performance gearing, or high altitude, in an auto tranny Jeep, you need lower gears than 5.38. 5.86 gears or 6.17 gears would be more appropriate for performance, and or high altitude use. Too bad they don't make 5.86 or 6.17 gears for our axles.

I live at 6000 feet elevation, at the base of a mountain that is 11,000 feet elevation, and I have 35" tires with 5.38 gears in my auto trans Rubi. Hate to say it, but it is still a dog. My Jeep downshifts just to make it over a freeway overpass. Another hundred horsepower under the hood would help.
__________________
2012 Ram 2500 Crew Cab 4x4: Cummins 6.7; 2" lift: 35s
2013 Wrangler Rubicon Unlimited: 6.4 Hemi; 3.5" lift; 35s
2014 Grand Cherokee Laredo: 3.6 Pentastar; stock; wife's Jeep
MoparToYou is offline   Reply With Quote
Unread 07-23-2010, 08:45 PM   #15
CooterBrown
Member
 
CooterBrown's Avatar
1965 CJ5 
 
Join Date: Nov 2009
Location: Lawrence, Kansas
Posts: 425
so then why does my stock JK rubicon fall into the yellow?
__________________
1965 CJ-5 all stock minus the tub

2010 rubicon JK
CooterBrown is offline   Reply With Quote
Reply

Tags
gear chart , gear/tire chart , JK Wrangler , wrangler
Thread Tools


Suggested Threads





Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.