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-   -   gearing dilemma (http://www.jeepforum.com/forum/f96/gearing-dilemma-1471293/)

xraypat23 01-30-2013 09:58 AM

gearing dilemma
 
So I just lifted my 2008 jk unlimited rubicon. Auto trans. I'm running 35x12.5x17 falken wildpeaks. It's a rubicon, and i've got the build sheet, so I know it has 4.10's in it. I'll never go bigger than 35. It's a daily driver, commuter, summer beach truck. My dilemma's in the gears. Highway's decent, sub 2000rpm at 65(recalibrated with AEV procal and speed verified by GPS). I'm getting right around 16.5mpg on the highway now. Probably 14mpg around town. Everywhere I go all I hear is 5.13, 5.13, 5.13. Is that really what I should do. I believe I could live with the 4.10's for a while, but i'd definitely like a little more pep. is 4.88 a better solution since i'll never go bigger? I don't want to be spinning at 2500+rpm to maintain highway speed. It's a decent chunk of change to spend, so I just want to do it right and do it once.

jstrubberg 01-30-2013 10:07 AM

5.13s. Do not get sucked into the idea that rpms are bad for this engine or that numerically higher gears will cost you gas mileage. Neither is true.

I run 5.13s, Mickey Thompson 315/70r17s and my average mileage is 16.5. That's about an 80/20 highway/city ratio in hilly mid-Missouri.

I cruise at 2500 rpm @ 70mph and the engine just purrs.

jwmbishop 01-30-2013 02:58 PM

I put 5:13s in - with idea to swap between stock 32s on road and 35s for off road (until the 32s are used up).

On the 35s its much like it was with 32s and 4.10 - on the 32s 5.13 it REAL peppy - but I see red line often when getting on the freeway etc.

Gonna go to 33s for on roads just to keep off the red and retain the pep.
Economy is 16ish on the 32s and 15ish on the 35s. I think highway suffers more than city...

brianjw 01-30-2013 03:08 PM

Some people have this retarded idea that an engine is only good for X amount of RPMs, and running higher rpms is going to kill the engine sooner. It's obviously not the case, running higher RPMs will circulate more oil, coolant, etc and with the 3.8 it will put the engine in its power band so it isn't working as hard, not lugging etc.

KrawlOff-Road 01-30-2013 03:22 PM

Pat,

I would do this:
http://www.krawloff-road.com/product_p/gearmaster.htm

With the 5.13's and never look back! LOL...

-Jason

neverhide34 01-30-2013 04:36 PM

And here you will hear it again... 5.13, 5.13, 5.13. You can't go wrong especially with a pre-2012 auto tranny.

JIMBOX 01-30-2013 04:39 PM

;) Good recommendation on the YUKON price, especially/w Master kits--

If you had a Rubi--5.38s/w auto are even better !

:tea: JIMBO

jwmbishop 01-30-2013 04:49 PM

Quote:

Originally Posted by JIMBOX (Post 14880432)
;) Good recommendation on the YUKON price, especially/w Master kits--

If you had a Rubi--5.38s/w auto are even better !

:tea: JIMBO

Yea - if I was only gonna see 34s or 35s I would have HATED myself for deciding 5.13.... but glad I went 5.13 - on 33s down it would have been brutal on my nerves to hear (okay who am I kidding - I am deaf) that little engine scream on 5.38s!

JIMBOX 01-30-2013 05:00 PM

;) Yeah, if you've gotta stick, but


Quote:

Originally Posted by jwmbishop (Post 14880505)
Yea - if I was only gonna see 34s or 35s I would have HATED myself for deciding 5.13.... but glad I went 5.13 - on 33s down it would have been brutal on my nerves to hear (okay who am I kidding - I am deaf) that little engine scream on 5.38s!

My '08 JKUR/auto/33.6" Hankooks--is heaven on 5.38s--2600rpm at 70 and towing is a pleasure !

:tea: JIMBO

jwmbishop 01-30-2013 05:18 PM

Quote:

Originally Posted by JIMBOX (Post 14880569)
;) Yeah, if you've gotta stick, but




My '08 JKUR/auto/33.6" Hankooks--is heaven on 5.38s--2600rpm at 70 and towing is a pleasure !

:tea: JIMBO

high side of 33s good then! (how often does your ECO light come on over 60 mph. Mine = seldom to never even downhill once the speedo goes over 60 (I don't think it will once the tach leaves that green range no matter what).

I know - its just another idiot light.

But what can I say - besides it amuses me so I must be an idiot....

robsbluerub 01-30-2013 05:19 PM

Xraypat- another thing to think about is performance on the beach. My rubicon with 35s and 4.10 gears isn't that good in the soft stuff. 4 high is too high and 4 low is too low. I even got the hot oil message running in 4 high with the wind. I'm going 5.38 as soon as I stop spending money on my project vehicle. I think that will help it in the sand.

1222 01-30-2013 06:28 PM

There’s a reason why 5.13s are the overwhelming choice for the 3.8, auto and 35s; for the last 6 plus years 5.13s are still the top choice. Sure, there are some that have deviated from that ratio but why mess with a proven combo? Gear selection is actually easy with the pre ‘12s. My previous Jeep was a ’08 JKU auto w/35s just like yours and I also had 5.13s.
:cheers2:

Jollydodger 02-01-2013 08:03 AM

Quote:

Originally Posted by jwmbishop (Post 14880505)
Yea - if I was only gonna see 34s or 35s I would have HATED myself for deciding 5.13.... but glad I went 5.13 - on 33s down it would have been brutal on my nerves to hear (okay who am I kidding - I am deaf) that little engine scream on 5.38s!

I run 5.38 with 33s (Duratracs) in the winter on the street and it's fine. I worried about it before I re-geared but it is no problem with an auto.

xraypat23 02-01-2013 08:30 AM

I'm thinking 5.13 is the right choice. Just don't want buyers remorse, it'd be an expensive decision to have to re do it! Glad to hear people are getting respectable mileage out of the 35, 5.13, auto combo.

JIMBOX 02-01-2013 08:40 AM

:D I get decent mileage ootta 5.38s and 33" tires too--


Quote:

Originally Posted by xraypat23 (Post 14889378)
I'm thinking 5.13 is the right choice. Just don't want buyers remorse, it'd be an expensive decision to have to re do it! Glad to hear people are getting respectable mileage out of the 35, 5.13, auto combo.

:cheers2: JIMBO


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