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Old 01-15-2020, 10:26 AM
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4.56s and 37s

Anybody have a video of the gauges running 37s and 4.5 gears with an automatic trans? Just want to see how it rides, what it takes to shift through the gears, how it maintains 100km/h

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Old 01-15-2020, 12:10 PM   #2
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I run 37's and 4.56 gears with a NAG1

At 70 MPH, I'm around 2700 RPM and 3000 RPM at 75 MPH. Under a load, the tach will get to about 4K before the first shift but will drop a bit earlier if you let off the gas.

If you plan on towing in the mountains, go 4.88's, other than that, it's not a bad fit. If I knew that I would have ever considered 37's when I had regeared (planned on 35's max) I would have done 4.88's.

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Old 01-15-2020, 02:52 PM
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I run 37's and 4.56 gears with a NAG1

At 70 MPH, I'm around 2700 RPM and 3000 RPM at 75 MPH. Under a load, the tach will get to about 4K before the first shift but will drop a bit earlier if you let off the gas.

If you plan on towing in the mountains, go 4.88's, other than that, it's not a bad fit. If I knew that I would have ever considered 37's when I had regeared (planned on 35's max) I would have done 4.88's.
Hmm. That's exactly where I am with 4.56s, I'd shift it manually if t was getting to 4k....

That actually sounds ok!?

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Old 01-15-2020, 02:52 PM
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Are you a 4 door?

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Old 01-15-2020, 02:54 PM   #5
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for 37s, i would go minimum 4.88. but, 5.13 are much better.
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Old 01-15-2020, 02:57 PM
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I know the chart, I'm trying to find someone to go through the gears on video so I can decide if I can live with the drag on the engine on the hiway

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Old 01-16-2020, 10:13 AM   #7
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I'm a 2 Dr.

I don't get it on the highway much any more. I'm a WFH person so it sits in the garage all week and on weekends, we use momma's GC trailhawk.

I do drive it (sometimes many, many miles), pulling a trailer when going wheeling so that's not a fair comparison for DD.
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Old 01-16-2020, 02:14 PM   #8
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3.6l/NAG1 4.56 is perfect for a DD with 37s in flatter areas. If I lived in a mountainous region i would go 4.88.
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Old 01-16-2020, 02:58 PM   #9
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I have 4.56's and 37's. I live in pretty flat country. I regeared when I was on 35's and it was good. I don't absolutely hate it, but no way would I ever go with my current setup knowing I was going to 37's. I got a great deal on the tires and could't pass them up. I run a 4 door. I never see ECO mode any more and very rarely drive over 65 mph, no matter what the speed limit as my gas mileage seems to go away above 2500 rpm. Currently get about 15 mpg versus the 17 to 18 with 35's. If you have a choice, go with the 4.88's or bigger if your axles will handle it.

As far as how it handles it is fine, but have had to replace the worn out lca's due to the occasional death wobble as the tires are quite a bit heavier. I got rid of most of it but still get it every now and then if the conditions are right. Gotta get under there and do some more work.
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Old 01-16-2020, 03:01 PM
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I put in 4.56s like 6 months ago and it's great for my 35x12.5x17s, it's good enough that I feel like I could do with a bit more tire, but i Do have a lot of hills in my area... it's a river valley. Maybe I'll buy a set of 37s just to beat on during trips

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Old 01-19-2020, 02:16 PM   #11
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I have 4.88s on 35s that actually measure 33.5" I like having a steeper than normal gear for my driving preferences. I am considering a 37 x12.50R17 patagonia milestar MT which measure about 35" for my next set and are only 2lbs heavier than what I have now. I would have went 5.13 off the start but I'm currently only on the D30 front with gussets and a powertrax no slip in it so I have to be a little careful with my wheeling too.
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Old 01-19-2020, 02:20 PM
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I have 4.88s on 35s that actually measure 33.5" I like having a steeper than normal gear for my driving preferences. I am considering a 37 x12.50R17 patagonia milestar MT which measure about 35" for my next set and are only 2lbs heavier than what I have now. I would have went 5.13 off the start but I'm currently only on the D30 front with gussets and a powertrax no slip in it so I have to be a little careful with my wheeling too.
Personally, If I run out of projects I plan to truss my d30 and wheel the snot out of it to prove it's way better than the credit it gets. I've still never seen a tube failure or diff housing break due to offroading. (Other than trail damage) I've seen many pics and videos of long armed, 37 wielding, skid plate shrouded tanks; built trail rigs, running dana30 front axles with tons of battle scarring and that d30nis plugging away happy as can be.

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Old 01-20-2020, 07:44 AM   #13
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Personally, If I run out of projects I plan to truss my d30 and wheel the snot out of it to prove it's way better than the credit it gets. I've still never seen a tube failure or diff housing break due to offroading. (Other than trail damage) I've seen many pics and videos of long armed, 37 wielding, skid plate shrouded tanks; built trail rigs, running dana30 front axles with tons of battle scarring and that d30nis plugging away happy as can be.

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This is good to know. I may sleeve and truss but so far I haven't felt the need. I do feel better with the gussets just because of the design of the C on my model. I do notice the JL has a redesigned C and I am wondering if it is more durable?
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Old 01-20-2020, 12:24 PM   #14
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My D30 is trussed and locked. I am nice to it but so far so good. Someday I will upgrade. Hopefully on my schedule and not the Jeeps...
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Old 01-20-2020, 12:50 PM   #15
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I have 4.88s on 35s that actually measure 33.5" I like having a steeper than normal gear for my driving preferences. I am considering a 37 x12.50R17 patagonia milestar MT which measure about 35" for my next set and are only 2lbs heavier than what I have now. I would have went 5.13 off the start but I'm currently only on the D30 front with gussets and a powertrax no slip in it so I have to be a little careful with my wheeling too.
So if 35's are really 33" and 37's are 35" and the charts are made based on actual tire size; why is it that if I want 37's, which are really only 35", does everyone say I need to beef up the axle if I'm a Dana 30 in front when the need for beefing up the Dana 30 really comes into play when you put 35's on your Jeep?
Especially when
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37 x12.50R17 patagonia milestar MT which measure about 35" ... are only 2lbs heavier
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Old 01-20-2020, 03:36 PM   #16
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So if 35's are really 33" and 37's are 35" and the charts are made based on actual tire size; why is it that if I want 37's, which are really only 35", does everyone say I need to beef up the axle if I'm a Dana 30 in front when the need for beefing up the Dana 30 really comes into play when you put 35's on your Jeep?
Especially when
The truth is likely somewhere in the middle. A typical 35 is really around 34" in diameter. The exception tends to be BFG KO2's and KM2's, they run smaller than the others. My BFG KO2 37's were about 35.5" in diameter, which is still bigger than just about every 35 but is only about an inch to an inch and a half bigger than most 35's. The Nitto RG 37's we now have are just over 36" in diameter. But there is a lot of grey area in measuring tires. Are you measuring the tire with the weight of the Jeep on it or unweighted? Are you measuring it aired up or aired down? Or are you going by the measurement that you need to put into the speedo to make it read right (which is even lower than with the weight of the Jeep on it)?
And the RPMs listed in the chart are based on actual working diameter. But the color codes seem to be more based on listed size than actual size. And the issues with running 37's and peoples experience with 37's breaking their D30 front axle, are based on listed size and not actual size.
It is a free country, do what you want. But even 35's can be an issue with a D30. Beyond that the risk simply goes up exponentially.
I worry about our 37's breaking with the 37's on it. We have upgraded ball joints, tie rod, and axle shafts. We still need hydro assist steering as it can be impossible to turn the steering wheel at times. That is on the list....
If we bend the housing I will upgrade. But so far we are good.
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Old 01-20-2020, 03:45 PM   #17
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I've got the 4.56 with 35's and would have preferred to have 4.88's. No chance of going to 37's without having 5.13's in my honest opinion. The 3.6 is not a low end torquey motor.
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Old 01-20-2020, 07:14 PM   #18
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The truth is likely somewhere in the middle. A typical 35 is really around 34" in diameter. The exception tends to be BFG KO2's and KM2's, they run smaller than the others. My BFG KO2 37's were about 35.5" in diameter, which is still bigger than just about every 35 but is only about an inch to an inch and a half bigger than most 35's. The Nitto RG 37's we now have are just over 36" in diameter. But there is a lot of grey area in measuring tires. Are you measuring the tire with the weight of the Jeep on it or unweighted? Are you measuring it aired up or aired down? Or are you going by the measurement that you need to put into the speedo to make it read right (which is even lower than with the weight of the Jeep on it)?
And the RPMs listed in the chart are based on actual working diameter. But the color codes seem to be more based on listed size than actual size. And the issues with running 37's and peoples experience with 37's breaking their D30 front axle, are based on listed size and not actual size.
It is a free country, do what you want. But even 35's can be an issue with a D30. Beyond that the risk simply goes up exponentially.
I worry about our 37's breaking with the 37's on it. We have upgraded ball joints, tie rod, and axle shafts. We still need hydro assist steering as it can be impossible to turn the steering wheel at times. That is on the list....
If we bend the housing I will upgrade. But so far we are good.
Thank you for the info.
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Old 01-20-2020, 09:24 PM   #19
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Thank you for the info.
Oh, I should add, we swapped out the stock D30 for a D44 out of a Rubicon when we decided to go with 37's. Even with the "baby" 37's that are the BFG KO2's. Unless you are a pure street Jeep I would not do 37's with the D30. If you figure when it fails you will upgrade, fine. But for us failure out on a trail would mean a bad day. And I don't like bad days. I still worry with the Rubi D44, but I worry less than I would with a D30 and 37's.
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Old 01-20-2020, 09:45 PM   #20
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Oh, I should add, we swapped out the stock D30 for a D44 out of a Rubicon when we decided to go with 37's. Even with the "baby" 37's that are the BFG KO2's. Unless you are a pure street Jeep I would not do 37's with the D30. If you figure when it fails you will upgrade, fine. But for us failure out on a trail would mean a bad day. And I don't like bad days. I still worry with the Rubi D44, but I worry less than I would with a D30 and 37's.
The only thing you gained was a larger ring and pinion and more splines on the axle shafts.
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Old 01-21-2020, 07:22 AM   #21
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The only thing you gained was a larger ring and pinion and more splines on the axle shafts.
Right. There is not a huge difference between the D30 and the D44. The axle tubes are supposedly the same size, along with the C's. The center pumpkin is bigger with the D44, to house bigger gears, and the axle shafts are a little stronger with more splines. The ball joints are the same between the two axles.
Ours has RCV axle shafts, stronger ball joints, and 4.88 gears (which some would be reluctant to put in a D30 due to the smaller size of the gears in the D30, that is the biggest difference). We also have an aluminum tie rod.
Even with all that, we still treat the axle carefully as I have no doubt if we aren't careful we could break it running 37's.
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Old 01-26-2020, 05:05 PM
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This is good to know. I may sleeve and truss but so far I haven't felt the need. I do feel better with the gussets just because of the design of the C on my model. I do notice the JL has a redesigned C and I am wondering if it is more durable?
Who can say. I do know one thing; the knuckles are made out of aluminum

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Old 01-28-2020, 11:53 AM   #23
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Can someone tell me how to identify the gearing in my jeep? I have 35 x 12.5 17’s and I can cruise at 40mpg in 5th. How can I look/tell? Or is it not possible once installed without opening it up?

I slowly turn onto my street, and roll stop signs in 3rd
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Old 01-28-2020, 01:26 PM   #24
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Jack up the rear wheels. turn a tire one revolution and count the revolutions of the driveshaft. If your driveshaft turns a bit under 3.5 revolutions, you have 3.21's. A bit over 3.5 revolutions, you have 3.73's, a bit more than 4 revolutions is 4.10's, 4.5 revolutions is 4.56 etc.

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