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Topic Review (Newest First)
03-03-2012 08:17 PM
zmotorsports
Quote:
Originally Posted by Yella View Post
With no regard to speed of the vehicle, what is the ideal rpm of the engine running down the highway mile after mile?
Generally speaking one would say at the lowest possible RPM, however, that is not necessarily the case. At too low of an RPM the transmission will hunt in/out of overdrive on an automatic. Also with too low of an RPM, especially in a high profile vehicle with a large frontal area like our Jeeps, the engine may be at a low RPM but the throttle position/ injector PWM (Pulse Width Modulation) may be at a point where it is actually lugging the engine and working it too hard at a lower RPM, this also creates more heat that the cooling system must expel. This is more detrimental to an engine than a higher RPM and working the engine less.

In my opinion on the 3.8 liter engine that is in a Jeep JK which is usually lifted (changing the frontal area) which drastically effects the drag of the vehicle and also loaded up with extra weight from bumpers, winches, tires/wheels and everything else we load them up with I think the 2400-2700 RPM range is the sweet spot for cruising.

Mike.
03-03-2012 07:13 PM
Yella With no regard to speed of the vehicle, what is the ideal rpm of the engine running down the highway mile after mile?
03-03-2012 06:34 PM
zmotorsports
Quote:
Originally Posted by TommyT View Post
My 2011 is a 6 speed manual with 3:21 gears. If I am reading this chart right, when I go to 33's, 4:10 gears would be ideal for my DD light trail use jeep, Yes or no? Any reason to go bigger?
That is correct, 4.10 gear ratio would be great for the 33" tire. Before you have them re-geared ask yourself if there is a chance that you will ever go larger, say 35" or even 37". If so now is the time to gear properly as it is not cheap to re-gear multiple times. If you think you will ever go larger I would go with 4.88 gears otherwise I would suggest the 4.10 ratio that you are thinking about.

There are many that just don't use sixth gear and run in fifth. You can do that, however, you will not be taking advantage of the mechanical advantage of proper gearing for your Jeep. I am a huge fan of getting the mechanical leverage back into the vehicle after altering tire size.

Mike.
03-03-2012 06:28 PM
zmotorsports
Quote:
Originally Posted by JKERS View Post
I am ready to tackle the re-gearing of my rig, I am not sure whether to go with 4.88's or 5.13's in my '11 JKU, automatic trans, 35" tires......anyone with any experience or insight would be much appreciated.."..
Is it the Rubicon model? Reason I am asking is front axle a d44 or d30?

If a d30 then I would go with the 5.13 gears. If a d44 (Rubicon) then I would go with the 5.38 gears.

In my opinion the 4.88 gears are what the automatic models should have come with from the factory. The 6-speed Rubicon models running 32" tires and 4.10 gears seem to be decent on the highway. They are running at near 2500 RPM. To get the automatic equiped JK to spin at that RPM they need a 4.88 gear with the 32" tires. Now jump up to 35" tires (actually measuring 33.75" in most cases) and you need to go to at least 5.13 preferabely 5.38 ratio.

My JKU runs right at about 2500 RPM @ 70 MPH on the interstate and the cruise hold fine with no hunting in/out of overdrive. My mileage went up after swapping out the 4.10 gears and around town it feels like a different Jeep. It actually can move out of its own way from a standstill vs. the 4.10 gears I thought I needed to push it to get it going.

Mike.
03-03-2012 02:54 PM
MTH
Quote:
Originally Posted by schnutzy

those are for the D30s in the JK, which is different from the D30s used in the YJ and TJ
Yeah, I figured he was talking about JKs, since this is the JK section. But looking at his profile, I see I'm probably mistaken.

Quote:
Originally Posted by TommyT
My 2011 is a 6 speed manual with 3:21 gears. If I am reading this chart right, when I go to 33's, 4:10 gears would be ideal for my DD light trail use jeep, Yes or no? Any reason to go bigger?
I wouldn't worry about regearing of you've got a 6 speed, particularly if you stick with a lightweight set of 33s. My 3.21s handle my 33s no problem--all I changed is that I don't bother with 6th gear anymore.

If you were going to go through the expense of a regear, you'd want to shoot higher than 4.10s. They'd produce a "stock-ish" performance that'd hardly be worth the cost. For 33s, you'd go for 4.56s and for 35s you'd go for 4.88s, either of which would give you better than stock performance. And if you're paying close to $2k, I've got to think you want it better than stock.
03-03-2012 12:46 PM
TommyT My 2011 is a 6 speed manual with 3:21 gears. If I am reading this chart right, when I go to 33's, 4:10 gears would be ideal for my DD light trail use jeep, Yes or no? Any reason to go bigger?
03-03-2012 12:37 PM
schnutzy
Quote:
Originally Posted by MTH View Post
I thought they make 5.XXs for the D30 now?
those are for the D30s in the JK, which is different from the D30s used in the YJ and TJ
03-03-2012 12:35 PM
MTH
Quote:
Originally Posted by denisbaldwin
I'm going with 4.88s myself so I can keep the Dana 30 up front.
I thought they make 5.XXs for the D30 now?
03-03-2012 11:11 AM
denisbaldwin I'm going with 4.88s myself so I can keep the Dana 30 up front.
03-03-2012 10:03 AM
pkmcd99
Quote:
Originally Posted by MTH
For 35s with the 3.8 and an auto trans, my reading leads me to believe 5.36 would be the best choice.

$4k? Prices I've seen are generally south of $2k, no?
Any shop ive looked into charges 10 hrs an axle plus parts and overnight lift fees. At 150 per hr, it adds up. Wish I had luxery of specialty shop that could do it cheaper and quicker
03-03-2012 10:02 AM
JIMBOX YUP, generally $1200 to $2000 bucks, depends on the shop and GEARS/warranty/labor rate and rebuild kits-

Mine was YUKON/lubelockers/Master install kits/Synergy Ball joints/Valvoline fluid--$1958 bucks

Can'tbeatem

JIMBO
03-03-2012 09:54 AM
MTH For 35s with the 3.8 and an auto trans, my reading leads me to believe 5.36 would be the best choice.

Quote:
Originally Posted by pkmcd99
Regearing certainly will put that arse dyno back where it should be, but I just cant justify 4k to switch both axles gear ratio out.
$4k? Prices I've seen are generally south of $2k, no?
03-03-2012 09:32 AM
JIMBOX I've gotta '08 JKUR/auto/ 33.6" tires-

I would never go with a regear LESS than 5.13 gears/w auto--mine is 5.38 and for cruising/towing/off-road-I'd never get even 5.13s-

My JKUR weighs 5200 lbs avg and my power is great/mileage is good/throttle response-IMMEDIATE/O/D use even when towing is substancial !

It's expensive, so doit right !

JIMBO
03-03-2012 08:27 AM
pkmcd99 After owning several Toyota trucks when I was younger, Ive come to the conclusion that most people on WF require to much power for how they drive. The toyota 22re is about one of the most tame four cylinder 4x4 power plants out there in its day. I had run 33-38.5 on various models and never regeared. Just compansated for power lost and drove according. The first generation JK with a 3.8l six banger is not a power beast, but even with the added weight, it still hauls better then my old yotas ever could. I dont believe running 34-35 tires is gonna suck the power any more then a yota on 38.5. Regearing certainly will put that arse dyno back where it should be, but I just cant justify 4k to switch both axles gear ratio out. Am I the only jeeper who thinks settling with stock gears is ok? I found on my yotas amd TJs for that matter, once you were in low range, you cant notice power robbing over sized tires, and out on the highway it isnt necessary to drive like you stole it. Dont gey me wrong, if I had the luxery to afford gears and labor I would be inclined to spend it, but in my world, stock is good enough for weekend warrior geo cache stuff.
03-03-2012 12:56 AM
Ricterslick I have a TJ running 35s and 5.13s. The pinon is small, but yay 5th gear. Glad I went so high.
03-03-2012 12:38 AM
kbwwolf
Quote:
Originally Posted by JKERS View Post
I am ready to tackle the re-gearing of my rig, I am not sure whether to go with 4.88's or 5.13's in my '11 JKU, automatic trans, 35" tires......anyone with any experience or insight would be much appreciated.."..
I'm with Rick. The 4.88's would be a waste of $$ for your rig with 35's.

Take a look at the chart below. It's pretty general, but will give you a rough idea of where you'll be, rpm-wise, with various tires at speed on the highway. Don't go by mfr tire size, though. You want actual size. For example, my 35's are really 34", so that's what I'd use.

03-03-2012 12:28 AM
rics1997 Well, you can get by with a 2012 and not regear but pre-2012 you really have to consider it. Especially a JKU. You might even get by with a 2 dr and 35's if you have a Rubi with 4.10 gears. But there really is a huge power drain with a JKU and 35's.

4.88 if 33's (and could still go to 5.13)
5.13 if 35's no question about it especially in a JKU

Have 4.88 and 33's and sometimes wish I went with 5.13 when towing. Freeway I am glad for 4.88.
03-03-2012 12:07 AM
Yella
Quote:
Originally Posted by JKERS View Post
I am ready to tackle the re-gearing of my rig, I am not sure whether to go with 4.88's or 5.13's in my '11 JKU, automatic trans, 35" tires......anyone with any experience or insight would be much appreciated.."..
I know you want to regear but look at this thread started by PieFace who doesn't want to regear.

http://www.wranglerforum.com/f33/wan...ar-141613.html

Now this was a thead intended for 2012 but it has lots of info about regearing in general and for 2012, <2012, auto and manual.
03-02-2012 09:36 PM
JKERS
4.88 or 5.13 gearing

I am ready to tackle the re-gearing of my rig, I am not sure whether to go with 4.88's or 5.13's in my '11 JKU, automatic trans, 35" tires......anyone with any experience or insight would be much appreciated.."..

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