4.88 or 5.13 Gears?

swiss_jeep

swiss_jeep

New member
Hi everybody,
I think about upgrading my JK to 37" Tires. Now my question is, would it be better to replace the factory 3.72:1 Gears (JK 09 Sahara) with the 4.88 or the 5.13's? I live in the mountains so I thought about the 5.13 but my questions now: what's about the fuel economy (is it much worse?) and is the Jeep runnig with much higher RPM (revolutions per minute)?
 
Ddays said:
D30 Axle = 4:88
D44 Axle = 5:13

Pinion gets real small on the D30 with the 5:13's.
Click to expand...

The front axle is a D30 and the rear one is a D44...so should I upgrade both on 4.88?
Now a stupid question: is it possible to put 4.88 in the front and 5.13 in the rear? Sorry for the stupid question...
 
swiss_jeep said:
Hi everybody,
I think about upgrading my JK to 37" Tires. Now my question is, would it be better to replace the factory 3.72:1 Gears (JK 09 Sahara) with the 4.88 or the 5.13's? I live in the mountains so I thought about the 5.13 but my questions now: what's about the fuel economy (is it much worse?) and is the Jeep runnig with much higher RPM (revolutions per minute)?
Click to expand...

37s, mountains, fuel economy.....I don't think so, Tim.

swiss_jeep said:
The front axle is a D30 and the rear one is a D44...so should I upgrade both on 4.88?
Now a stupid question: is it possible to put 4.88 in the front and 5.13 in the rear? Sorry for the stupid question...
Click to expand...

Only if you remove your driveshafts. This will prevent any damage to the gear boxes.
 
swiss_jeep said:
The front axle is a D30 and the rear one is a D44...so should I upgrade both on 4.88?
Now a stupid question: is it possible to put 4.88 in the front and 5.13 in the rear? Sorry for the stupid question...
Click to expand...

LOL - I almost posted a smartass response but bit it off.

No, you can't run different gears in the front and rear - they have to match or one axle would be trying to turn at a different speed than the other.
That in turn means real expensive parts break....
 
My last build was a 2010 JKU Sport and I ran 5:13s with no problem. I live in Colorado and the altitude and mountains play hell on the 3.8 motor. I ran that set up on 37s for 2 years before I started my new build. I ran Holy Cross 2, Chinaman's 5+ times and most other trails around Colorado. Not one time did my Dana 30 give out on me with 5:13. This is just my experience but I like to hear from others that have run a set up that I would like to go to. I did upgrade my front axel with sleeves, gussets and upgraded ball joints when I moved to 37s though. ImageUploadedByWAYALIFE1468352467.284472.jpgImageUploadedByWAYALIFE1468352503.499857.jpg
 
swiss_jeep said:
Well, now on 33" I have 20MPG if I drive with 40-50mph over the mountain pass (10'000 feet over sea)...I think that's really good.
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That's pretty good. But yes, 37s will make that go to shit. But you're Jeep will look cooler and you will feel cooler. It's a Jeep.
 
37s in Colorado with my 3.8 gave me around 14 average in city and mountain drives. Sometimes it would defiantly dive in to the 11 and 12 mpg realm. But if you making he leap to a bigger jeep then it's not miles per gallon it's smiles per gallon!!
 
Ddays said:
LOL - I almost posted a smartass response but bit it off.

No, you can't run different gears in the front and rear - they have to match or one axle would be trying to turn at a different speed than the other.
That in turn means real expensive parts break....
Click to expand...

Yea I thought so LOL but I simply had to ask it anyway ;)

Now what's about the RPM and the fuel economy? Is it right that with the 4.88 Gears the RPM is higher because the engine has to work "more" to rotate the tires 1 time. But it's lighter for the car to turn the wheels (because the lower gears) and so the fuel economy should not rise very much...
What are your experiences?
 
swiss_jeep said:
Yea I thought so LOL but I simply had to ask it anyway ;)

Now what's about the RPM and the fuel economy? Is it right that with the 4.88 Gears the RPM is higher because the engine has to work "more" to rotate the tires 1 time. But it's lighter for the car to turn the wheels (because the lower gears) and so the fuel economy should not rise very much...
What are your experiences?
Click to expand...

My experience can only be compared to having proper gearing after using stock gears while running larger tires. My current situation is comparing to that. I changed tires as soon as I bought it so I never had a stock application to compare too. And this is a WJ not a JK.

There are so many variables and circumstances when it comes to fuel mileage so it's hard to give a definitive answer. I noticed on mine, on the highway rpms were higher and fuel mileage went down. In the city, it seemed to go up just a little bit (I assume gears are making the engine/trans work less with the larger tires). The vehicle's power definitely felt better. On hills, it depends on the grade, sometimes I get good mpg, sometimes bad in the mountains, too many factors IMO.
 
WJCO said:
My experience can only be compared to having proper gearing after using stock gears while running larger tires. My current situation is comparing to that. I changed tires as soon as I bought it so I never had a stock application to compare too. And this is a WJ not a JK.

There are so many variables and circumstances when it comes to fuel mileage so it's hard to give a definitive answer. I noticed on mine, on the highway rpms were higher and fuel mileage went down. In the city, it seemed to go up just a little bit (I assume gears are making the engine/trans work less with the larger tires). The vehicle's power definitely felt better. On hills, it depends on the grade, sometimes I get good mpg, sometimes bad in the mountains, too many factors IMO.
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^^ This.

Oddly enough, I got better gas mileage on I-70 through the Colorado mountains than I did in Kansas. :thinking: Doesn't make any sense....
 
I have seen the gear chart for an Auto 3.6, but what RPMs are you 37" guys running at 70mph with the 5:13's? That gear chart isn't quite matching up with my tire and gear set
 
Hammmerhead said:
I have seen the gear chart for an Auto 3.6, but what RPMs are you 37" guys running at 70mph with the 5:13's? That gear chart isn't quite matching up with my tire and gear set
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If you're running 37s try looking at the RPM for 36" tires or even between 36" and 35" tires.
 
right now with 35s and 5.13 gears I am getting 17 mpg. But I did blow the front end 4000 miles after regearing my dana 30, so basically dont expect 5.13s in a dana 30 to last
 
Hammmerhead said:
I have seen the gear chart for an Auto 3.6, but what RPMs are you 37" guys running at 70mph with the 5:13's? That gear chart isn't quite matching up with my tire and gear set
Click to expand...

Cruising on a flat I'm running under 3000, maybe 2800 or so
 
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