Gears for 37" tires

[WK2JT]

I ran 4:88's and put 80k miles on that Jeep, MUCH of it Hwy on trips to Ca, Nv, Moab, Rubicon, Death Valley Baja you name it....That said it was a TJ and Bulletproof 6. That is down-low for both HP/Torque, you get nearly 80% of your torque just off idle and time that engine gets North of 3000 rpm is gasping for air. BUT the V6 does not eve come alive until you get beyond 3000 rpm. Were it my build I would go 5:13 -5:36 cogs because the V6 don't get happy until it goes upstairs in the rpm band. Down side is mpg, but if you bought for mpg you may have bought the wrong thing. Let me add, if you plan on running the serious big boy pants trails 4+ level I would reach deep and go 5:36...WHY? Slow rolling does not provide a lot of RPM's and you need make them thru the gears.

Agreed about the V6. It seems happy in the 2,400-2,800 range on the hwy. Surprisingly, my MPG got better with the 5.13’s compared to the 3.73’s with the 37’s. It’s certainly not back to stock MPG, but doing approx 19 on the highway at 65. Over 70 and areo, or the lack there of, takes over.

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[Rampager]

I’m running 4.56 gears with 38” tires (measure more like 37.5”) on my gladiator with a 6 speed manual. I did the calculations and I is very close to the same as when it had 31.5” tires and 3.73 gears. I feels very similar shifting and driving. Holds its speed very well on the highway. Runs right around 2000rpm at 70mph in 6th.

 

[93civej1]

I have a max tow with the 4.10's of course, and 315/70/17 KO2.
I saw someone say they are running a rubicon with 37's and fuel mileage and experience are not much different than stock.

Please tell me how so? Mine with a diameter of 34.4 and weight of 62 and stock wheels, does not drive anywhere like stock. It stays in a lower gear going up hills and higher RPM. Gas mileage has dropped on the screen. Stock i was getting 21 - 22 around town and highway....and now I see 17-18 with normal driving. I took a trip to north east TN the other day and after the trip my average on screen was right around 16.9.

I want to know how 37's on 4.10 could drive and fuel like stock? someones full of crap.

 

[FLUndertaker]

I have a max tow with the 4.10's of course, and 315/70/17 KO2.
I saw someone say they are running a rubicon with 37's and fuel mileage and experience are not much different than stock.

Please tell me how so? Mine with a diameter of 34.4 and weight of 62 and stock wheels, does not drive anywhere like stock. It stays in a lower gear going up hills and higher RPM. Gas mileage has dropped on the screen. Stock i was getting 21 - 22 around town and highway....and now I see 17-18 with normal driving. I took a trip to north east TN the other day and after the trip my average on screen was right around 16.9.

I want to know how 37's on 4.10 could drive and fuel like stock? someones full of crap.

Yes they are.

 

[KurtP]

I have a max tow with the 4.10's of course, and 315/70/17 KO2.
I saw someone say they are running a rubicon with 37's and fuel mileage and experience are not much different than stock.

Please tell me how so? Mine with a diameter of 34.4 and weight of 62 and stock wheels, does not drive anywhere like stock. It stays in a lower gear going up hills and higher RPM. Gas mileage has dropped on the screen. Stock i was getting 21 - 22 around town and highway....and now I see 17-18 with normal driving. I took a trip to north east TN the other day and after the trip my average on screen was right around 16.9.

I want to know how 37's on 4.10 could drive and fuel like stock? someones full of crap.

im on stock 4.10’s and 37’s. people who say its fine are nuts. Ive got Dana 4.88’s on order. Waiting for them to show up.

it cant come soon enough, either.

 

[Ole Cowboy]

I have a max tow with the 4.10's of course, and 315/70/17 KO2.
I saw someone say they are running a rubicon with 37's and fuel mileage and experience are not much different than stock.

Please tell me how so? Mine with a diameter of 34.4 and weight of 62 and stock wheels, does not drive anywhere like stock. It stays in a lower gear going up hills and higher RPM. Gas mileage has dropped on the screen. Stock i was getting 21 - 22 around town and highway....and now I see 17-18 with normal driving. I took a trip to north east TN the other day and after the trip my average on screen was right around 16.9.

I want to know how 37's on 4.10 could drive and fuel like stock? someones full of crap.

TRUST me on this THEY KNOW IT!

Only been on Jeep forums for a few years going back to around 1980 or so.

Here are some given's based upon my observations:
The bigger the tires and deeper the gears = increased MPG: Bigger taller tires cut thru the air badder than skinny OEMs

The higher the lift (6inchs +++) the higher the MPG: Higher you can get your barn door up in the air the better the barn door beats the air into submission creating better MPG. Added side benefit: For ever 1 inch you lift beyond 3 in your Richard grows 2 in and wives and girlfriends will pay for your lift they are so giddy.

Cold Air Sytems the more it costs will increase MPG to high that gasoline starts to run out of the fill opening when you drive and the added HP/Torque is so great that you have been banned from all off road trails since your power will literally rip the rocks off the face of the earth.

Every thread on MPG the longer people post the higher the MPG, bigger the tires and higher the lifts go. Won't mention the Forum, but just read it about a week ago: '42 in tires 6.5 lift, 5:36 gears and mpg when from OEM 16.x to 22.1 on the highway averaging 85 mpg on a 1200 mi trip.'

This is the Gospel truth I read on the Jeep Forums so it must be true...if you don't you will openly attacked by him and his buddies who all have done same.

 

[hjdca]

I just got my Dana 5:13s installed yesterday with my Adam's driveshaft on my manual JTR to support my 37" Goodyear MTRs. The power is fantastic. I drove it up to Frazier Park and altitude and Mountains make the gears shine ! I will try to net it out for you:

1. 4:88 or 5:13, you will be happy. Both will make a huge difference in Performance.
2. If you live in the mountains like me and are at elevation like me, then, 5:13s
3. If you live on the flat land and low elevation, then, 4:88s.
4. If you are towing, then, 5:13s

 

[FLUndertaker]

I just got my Dana 5:13s installed yesterday with my Adam's driveshaft on my manual JTR to support my 37" Goodyear MTRs. The power is fantastic. I drove it up to Frazier Park and altitude and Mountains make the gears shine ! I will try to net it out for you:

1. 4:88 or 5:13, you will be happy. Both will make a huge difference in Performance.
2. If you live in the mountains like me and are at elevation like me, then, 5:13s
3. If you live on the flat land and low elevation, then, 4:88s.
4. If you are towing, then, 5:13s

Thanks for the gear input. Why the driveshaft change?

 

[hjdca]

Thanks for the gear input. Why the driveshaft change?

For heavy 4wheeling, A front Driveshaft change is recommended for any lift 3.5" and above. It is because of the bad CV angle and boot by the transfer case and at full articulation while wheeling, the stock driveshaft is too short.

 

[Renegade]

For heavy 4wheeling, A front Driveshaft change is recommended for any lift 3.5" and above. It is because of the bad CV angle and boot by the transfer case and at full articulation while wheeling, the stock driveshaft is too short.

Yes, with front shocks longer than 28.5, the driveshaft may also come into contact with the automatic transmission pan and/or the front skid crossmember.

 

[Marine2947]

I have a JTR auto. Have a RK Pro No limits 3 inch lift, 37 inch Trail Grapplers on 17s and 4.88 gears on order. I tow a tear drop trailer (3k pounds loaded) and I overland all over (mountains, desert etc) and it’s also my daily driver. Should I stick with the 4.88 or go 5.13? Kinda want the jack of all trades gearing since I also plan to overland without the trailer to get into some more technical stuff. Thanks again for any info/opinions.

 

[hjdca]

I have a JTR auto. Have a RK Pro No limits 3 inch lift, 37 inch Trail Grapplers on 17s and 4.88 gears on order. I tow a tear drop trailer (3k pounds loaded) and I overland all over (mountains, desert etc) and it’s also my daily driver. Should I stick with the 4.88 or go 5.13? Kinda want the jack of all trades gearing since I also plan to overland without the trailer to get into some more technical stuff. Thanks again for any info/opinions.

I went 5:13s because I have a manual JTR and I wanted a little extra torque down low and a really really low first gear in low range for rock crawling. The power difference with 5:13s is substantial vs. stock with 37s. If you are towing anything, I would go 5:13s.

What is your normal top end speed on the fwy? If you are going 85 mph and are not towing on flat ground or downhill, then, you might get better mileage with 4:88s, but, I am not sure. At 85, with 5:13s and 37s, and the manual, I am at about 2900 rpm. Remember, the manual has a lower 6th gear than the 8th gear in the auto, so, the auto will be at approx. 2800 at 85 mph.

 

[FLUndertaker]

I went 5:13s because I have a manual JTR and I wanted a little extra torque down low and a really really low first gear in low range for rock crawling. The power difference with 5:13s is substantial vs. stock with 37s. If you are towing anything, I would go 5:13s.

What is your normal top end speed on the fwy? If you are going 85 mph and are not towing on flat ground or downhill, then, you might get better mileage with 4:88s, but, I am not sure. At 85, with 5:13s and 37s, and the manual, I am at about 2900 rpm. Remember, the manual has a lower 6th gear than the 8th gear in the auto, so, the auto will be at approx. 2800 at 85 mph.

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Thanks for this. I am so on the fence between the 488 and 513. If 488 gets me close back to factory with 37s then I am leaning tiwards 513. I rarely do much highway driving mostly surface streets and I think the 513 will give me more right out of the hole. Mine an auto.

 

[hjdca]

Thanks for this. I am so on the fence between the 488 and 513. If 488 gets me close back to factory with 37s then I am leaning tiwards 513. I rarely do much highway driving mostly surface streets and I think the 513 will give me more right out of the hole. Mine an auto.

5:13's in the city will give you good gas mileage and more torque than 4.88s. Your auto will get to 8th gear quickly. 65 mph is a pretty good sweet spot for gas mileage with the 5:13s.
I went with Dana Spicer gears. They are a lot more expensive than other brands, but, the whole experience has been delightful. I just changed my rear gear oil at 800 miles, and everything looks perfect.

 

[Marine2947]

I went 5:13s because I have a manual JTR and I wanted a little extra torque down low and a really really low first gear in low range for rock crawling. The power difference with 5:13s is substantial vs. stock with 37s. If you are towing anything, I would go 5:13s.

What is your normal top end speed on the fwy? If you are going 85 mph and are not towing on flat ground or downhill, then, you might get better mileage with 4:88s, but, I am not sure. At 85, with 5:13s and 37s, and the manual, I am at about 2900 rpm. Remember, the manual has a lower 6th gear than the 8th gear in the auto, so, the auto will be at approx. 2800 at 85 mph.

I’ll be doing a lot of highway driving and usually hit around 70/75 when I’m going steady.

I went 5:13s because I have a manual JTR and I wanted a little extra torque down low and a really really low first gear in low range for rock crawling. The power difference with 5:13s is substantial vs. stock with 37s. If you are towing anything, I would go 5:13s.

What is your normal top end speed on the fwy? If you are going 85 mph and are not towing on flat ground or downhill, then, you might get better mileage with 4:88s, but, I am not sure. At 85, with 5:13s and 37s, and the manual, I am at about 2900 rpm. Remember, the manual has a lower 6th gear than the 8th gear in the auto, so, the auto will be at approx. 2800 at 85 mph.

I’ll be doing a lot of highway driving with moderate trails/overlanding. I have an auto. Is 4.88 a good sweet spot for that?

I went 5:13s because I have a manual JTR and I wanted a little extra torque down low and a really really low first gear in low range for rock crawling. The power difference with 5:13s is substantial vs. stock with 37s. If you are towing anything, I would go 5:13s.

What is your normal top end speed on the fwy? If you are going 85 mph and are not towing on flat ground or downhill, then, you might get better mileage with 4:88s, but, I am not sure. At 85, with 5:13s and 37s, and the manual, I am at about 2900 rpm. Remember, the manual has a lower 6th gear than the 8th gear in the auto, so, the auto will be at approx. 2800 at 85 mph.

I’ll be going about 70/75 mph highway and doing a lot of highway driving with moderate trails/overlanding. I normally driving long distances to hit different areas around the western part of the US. Is 4.88 a good happy medium for that?

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