Ordering gear set today

[USMC-SSGT]

Just need some validation. I’ve read arguably every thread for the last 5 months and “decided” on 4.56 on 35s.

Stats:
-overland on 3.73
-35” MT Baja boss with 2.5” lift
- live at sea level 1 mile from the ocean
-no load or heavy gear
-no towing other than a utility trailer a few times a year.
-daily driver
-70/30 around town and a 1x/weekly 80 mile highway round trip at 75mph

What I want:
-overdrive back
-ability to merge onto the highway and the truck shifting instead of winding out to 5k rpm’s before up to speed
-ability to go up a 3% grade without downshifting to 5th/6th
-use adaptive cruise and not have it downshift 3 gears when it needs to go from 73 back to 75mph
-tow my little trailer out of 5th gear
-best mpg possible. That may end up being 15…I’m ok with that and would take that over 14. Not looking for a Prius, but a best case scenario.

Lastly:
- this Jeep doesn’t wheel, ever. My Cj does. This one gets me down my logging road to get to camp.
-I’m not looking for best performance. Don’t need to beat anyone off the line because I drive like an 80 year old. (Not the kind that mistakes the gas for the brake and drives through the front of a 7/11)
-I may do 37s in 50k miles when my MT wear out. I’d do light ones, and may not even do this at all.

What I’ve come up with based on all my reading- 4.56 is ideal for 35s. If you EVER want to go 37s, do 4.88. However looking at this chart, and being unloaded, not towing, sea level, and not wheeling, it looks like 4.56 could be optimum for either tire under my set of circumstances. I want to keep the RPMs lower and keep the performance closer to OEM.

Experts, what do you think? I am not married to any idea, just going to make the purchase and want to do my best diligence. Reason for this thread being that ALWAYS 4.88 doesn’t necessarily mean always as there are difference scenarios which could call for something else. Looks like based on this chart, in a vacuum,
37s on 4.56 would behave like factory 33s on 4.10.

Note: I used actual inches for simple math, not measured tire size

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[USMC-SSGT]

Also- does brand really matter based on the 3-5 available? I happen to be looking at revolution gears because I can get a small discount on them. There is also Yukon and spicer. Seems from my reading that you can basically throw a dart and where it lands is fine between the group.

 

[Chris262]

If you're going for heavier D load rated or higher tires I would go for the 4.88s. At 37s you have some lighter options but they're limited compared to the heavier duty tires.

 

[OMTBiker]

For your intended use cases 4.56 is an excellent choice, they are slightly over geared for 35s but will work fine. If you choose a light 37 in the future the gearing is barely below stock Rubicon gearing and should be adequate.

 

[USMC-SSGT]

For your intended use cases 4.56 is an excellent choice, they are slightly over geared for 35s but will work fine. If you choose a light 37 in the future the gearing is barely below stock Rubicon gearing and should be adequate.

This is what I am thinking and looking to confirm. I don’t necessarily want to be over geared for 35s as that’s likely where I’ll stay (and am.) They are heavy 35s though at 73lbs each. That gives me some comfort being slightly over geared spinning so much mass. The plus side is that the weight gives me some room to play with at the 37” range where If I go that route I could likely stay +- a few lbs.

Definitely don’t want to waste the money and do something like 4.10s though for the 35s. The only exception being if I could find some like new rubicon axles for cheap money. I could likely swap those myself in my garage. That’s a needle in a haystack though so not putting a lot of thought into it.

 

[USMC-SSGT]

I’m going to assume that if my line of thought was way off, the peanut gallery would have lit this thread up. 4.56 it is!

 

[Wheelin98TJ]

I'd do 4.88. I might even do 5.13 for mine with 35s.

RPM with 4.88 will be about 2,300 at 70. You don't want much lower RPM if you're trying to cruise in 8th.

 

[USMC-SSGT]

I'd do 4.88. I might even do 5.13 for mine with 35s.

RPM with 4.88 will be about 2,300 at 70. You don't want much lower RPM if you're trying to cruise in 8th.

According to the chart, wouldn’t it be closer to 2500 with 35s and 4.56? That should be solidly into 8th. Even on 37s with 4.56 it’s 2400.

4.88 on 37s shows nearly 2600.

All my info is based on months of research and investigation as well as speaking with shops. I have zero practical knowledge so maybe you could fill me in on what I’ve missed?

 

[Mac]

Who will you have do the swap, what will it cost?

 

[USMC-SSGT]

Who will you have do the swap, what will it cost?

Most likely Ratchets in NH. They are very well known and quoted around $2400.

My dealer in Portsmouth actually quoted $2400 as well and will warranty the work, but not the aftermarket gears. Leaning towards ratchets however because this is their speciality. Uncertain of the level of gear change experience the dealer would have.

Off-road elements south of Boston is another incredible shop, and quoted $2400 also. They are about 1:20 drive from me. Ratchets is :40 and the dealership is :20.

In the northeast these are as good a price as you’ll find. Unfortunately we don’t get the $1500-$1800 quotes west of Mississippi gets.

 

[Wheelin98TJ]

According to the chart, wouldn’t it be closer to 2500 with 35s and 4.56? That should be solidly into 8th. Even on 37s with 4.56 it’s 2400.

4.88 on 37s shows nearly 2600.

All my info is based on months of research and investigation as well as speaking with shops. I have zero practical knowledge so maybe you could fill me in on what I’ve missed?

I used an RPM calculator with 34.5” for the tire size and 0.67 for the OD ratio. Then rounded the results up to the next 100. It’s normally pretty accurate.

I’ll check my RPM at 70 in 8th and double check the numbers. It might end up being closer to 2,400 with 4.88.

4.56 will definitely not be 2,500 RPM at 70. I had a rig with 4.56 and 35s and it was 3,200 RPM at 70 with a 1:1 transmission ratio. So you’d turn 2/3 that in 8th gear.

 

[USMC-SSGT]

I used an RPM calculator with 34.5” for the tire size and 0.67 for the OD ratio. Then rounded the results up to the next 100. It’s normally pretty accurate.

I’ll check my RPM at 70 in 8th and double check the numbers. It might end up being closer to 2,400 with 4.88.

4.56 will definitely not be 2,500 RPM at 70. I had a rig with 4.56 and 35s and it was 3,200 RPM at 70 with a 1:1 transmission ratio. So you’d turn 2/3 that in 8th gear.

Good info. I know charts sometimes can be as accurate as the MPG listed on a sticker.

 

[USMC-SSGT]

What’s that chart based on for rpm? 8th gear? For fun I tried to take a snap of 7th and 8th with 3.73 and 35” tires. Not an exact science though because RPM fluctuates with any rise or fall of the road or wind. Helps verify the accuracy of the chart. 8th was about 1900 and 7th was about 2100.

 

[Wheelin98TJ]

It looks like 1,800 in the pic, but 18-1900 close enough.

So your RPM with 4.56 will be 2,200-2,300.

RPM with 4.88 is 150 RPM higher than 4.56 at 70 MPH. So 2,350-2,450 with 4.88.

The chart appears to be using an OD ratio that is about 0.85. Could be it's a chart for the 6 speed manuals since they have a 0.84 OD ratio.

 

[USMC-SSGT]

Good point about the chart. Hard to be certain of the final drive ratio of .67.

Grim jeeper seems to take out some of the variables where I could ensure the transmission and drive ratio of 8th. Looks like it checks out solid with your numbers. Round about way to get there, but looks still like still a good ballpark. Long story short- 4.56 *should* put me in the ballpark numbers of a stock rubicon/mojave/max tow. I’ll be about 100+ rpm or so higher in OD. Even if I run some lighter 36.5” actual BFG, it puts me closer to a factory 4.10 setup. Likely closer to the feel of those with 4.10 gears running 35’s. Good, not great. To make a long story much longer, it sounds like 4.56 is likely ideal under my current setup, driving habits, geolocation, what I’m looking to get out of it. If and when I go 37, I’ll likely need to be aware of the weight and actual measured height.

This chart should be within +-150 rpm factoring for human error of me having a parameter wrong.

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