Do Yourself a Favor - Regear Your 2012-Up JK!!

IBeHeWhoIsJoshua

IBeHeWhoIsJoshua

New member
JKWrang said:
Yea, we said the same thing. :beer:
I dont have an eco light tho. Just a green area where acceptable rpm are on my tach. Same thing

Sent via secret squirrel underground network.
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My '13 sport has both. When I drive our '11 Avenger I look for the stupid Eco light it doesn't have haha
 
wayoflife

wayoflife

Administrator
Staff member
I just saw this post that Dynatrac made in another thread and felt that it would be good to post it here as well:

Dynatrac said:
When choosing gear ratio’s I notice that many folks are too conservative. The popular calculations out there will show you the RPM change at a given speed, but that is not the whole answer.

The size of tires varies greatly. If the sidewall says 35” or 37”, it is just an estimate. Reputable tire manufacturers like BFG, have more detailed data on their websites for each tire, but even that is still an estimate.

Inflation pressure and vehicle weight compress the bottom of the tire. It is different for every tire on every car. The number that is most accurate is called Static Loaded Radius (SLR). That is the distance from axle CL to the ground when the car is loaded, and the tire is inflated to a given pressure. You can measure this yourself in your driveway. Multiply that measurement x2 to get a more accurate tire diameter for your calculation.

The other factor to consider is that tires rolling on pavement create friction and drag. Larger tires create more friction and drag. Lift kits also increase frontal area that adds wind resistance.

Some folks think that if the engine turns slower they will save fuel. Not necessarily. The engine is designed to be most efficient in a given power band. The factory makes this decision to conform to Federal fuel economy laws (CAFE). If the ratio is too high (low numeric number), then the engine will lug, and burn more fuel. The transmission will also spend less time in OD, and hunt in and out frequently. Also bad for fuel economy.

When you do your calculation, you are better off having the engine spin somewhat faster than stock (higher numeric gear ratio, aka lower gear). That will maintain optimal fuel economy, and overcome the wind drag from higher body height, and rolling resistance of the bigger tires on pavement. It will also make the car far more fun to drive. It will feel lively and responsive.
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:yup:
 
E

espi

New member
wayoflife said:
I just saw this post that Dynatrac made in another thread and felt that it would be good to post it here as well:



:yup:
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I plan to move up to 285/75r17 Toyo AT2s soon and have been debating on getting gears done when I have trutracs installed. So the question is where is that RPM band? I have 3.73 gears and drive 75-80mph on the highway. Would 4.56 gears benefit me? This is my DD and we only run pineland trails and the beach.
 
wayoflife

wayoflife

Administrator
Staff member
espi said:
I plan to move up to 285/75r17 Toyo AT2s soon and have been debating on getting gears done when I have trutracs installed. So the question is where is that RPM band? I have 3.73 gears and drive 75-80mph on the highway. Would 4.56 gears benefit me? This is my DD and we only run pineland trails and the beach.
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Even if you don't plan on ever going any bigger, I personally would recommend that you go with a 4.88 and based on what Dynatrac was saying above.
 
E

espi

New member
wayoflife said:
Even if you don't plan on ever going any bigger, I personally would recommend that you go with a 4.88 and based on what Dynatrac was saying above.
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Wow, I would not have even thought of 4.88 for 34s. That would put my RPM at 3300 @ 80mph.

Is this a non issue because anything over 70mph and your fighting wind resistance?
 
M

mrmike

New member
What would be recommended for more desert driving than crawling. Also we typically have a fair amount of highway driving to get to the trails.

2012 JKUR. Just mounted my nitto 37's. The 35s with the 4.10s are decent. 37s much less so.
 
wayoflife

wayoflife

Administrator
Staff member
espi said:
Wow, I would not have even thought of 4.88 for 34s. That would put my RPM at 3300 @ 80mph.

Is this a non issue because anything over 70mph and your fighting wind resistance?
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As Dynatrac pointed out, there are a lot more things to consider than just what a chart tells you.

mrmike said:
What would be recommended for more desert driving than crawling. Also we typically have a fair amount of highway driving to get to the trails.

2012 JKUR. Just mounted my nitto 37's. The 35s with the 4.10s are decent. 37s much less so.
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As you will note, I had 5.13's installed on my 2012 and I'm running 37's. I do a ton of driving and already have over 77,000 on my odometer and a lot of that is out in the desert just as much as crawling.
 
Cschueren

Cschueren

New member
2012 Rubicon 2 dr Manual

So you would recommend 5.13 for 37"

I am frantically getting everything ready for my build and I think this is the last big item
 
Cole Trickle

Cole Trickle

New member
I'm hoping I have the same results with 5:13's

I just had Off Road Evolution throw them in on Monday. Drew took care of the whole deal and made it painless.

Dropped off at 8:30am and it was ready later the same afternoon. I only have 20 miles on it so far but I can already tell the 37's are going to like this new program 500% better.:):cool:
 
G

GENREC

Member
Can I get some piece of mind here. I have a 2014 JKU Sport, so D44 rear, D 30 frott. Going 2.5 lift, 35's. This is pretty much a DD. Being told 4.56 and 4.88 gears from various shops..after my homework Im leaning 4.56 gears for the better MPG since I drive 60+ miles a day. You all agree?
 
noroad

noroad

New member
GENREC said:
Can I get some piece of mind here. I have a 2014 JKU Sport, so D44 rear, D 30 frott. Going 2.5 lift, 35's. This is pretty much a DD. Being told 4.56 and 4.88 gears from various shops..after my homework Im leaning 4.56 gears for the better MPG since I drive 60+ miles a day. You all agree?
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is it an auto (if so 4.88s)
plan on going bigger then 35s(if so 4.88)
 
Wethy

Wethy

Member
wayoflife said:
Well, it's what I've run in the past and what I'm running in my 2012 JK now :yup:
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random question. did you re-gear moby after the LS swap? just curious i dont remember reading it in the thread about the swap but there was a lot of info in that post
 
Wethy

Wethy

Member
wayoflife said:
No. Still running 5.38's
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really??? that to me would seem a little steep. i mean with a 6.2 shouldnt you be able to gear down(numerically) i mean a 5.7hemi with 35's and 3.92 has no problem power to the wheels :S. but thats in a 1500 ram. obviously thats not 40 inch tires with a monster full float axle in the rear and a lot of heavy mods. is there a particular reason you stayed that high? other than the fact it possibly helps keep the mpg's up? im just curious now :idontknow:
 
Robicon

Robicon

Member
wayoflife said:
I just saw this post that Dynatrac made in another thread and felt that it would be good to post it here as well:



:yup:
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Honestly, this kind of info is invaluable for nubs like me. I'm into tech sales (smart card stuff) and look for the logic in why this does that and the benefits. Thanks for sharing this awesome post, this whole thread gives great info from personal experience.

Rob
 
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