Be careful where you drive your Earthroamer's...

[charlieaarons]

If your TC is one of the alloy chain-drive ones ubiquitous the last 20-25 years, it’s ~2.7:1. “Black box underdrive” is a short ~6” w/adapter gearbox that goes between transmission and transfer case. It’s only for trans/TC up to 350/3500 size vehicles. With a symmetric 6 bolt pattern between trans and TC. The 450/550 vehicles use a 8 bolt pattern.
What’s your vehicle?
If you have a F350, consider something like

Blackbox NP205 Titan

The Current BlackBox Build Time is 12 Weeks BlackBox TITAN – Strength Redefined The BlackBox Titan was built with one mission: unmatched strength. With a CNC-machined 6061-T6 billet aluminum case and a massive 1.75" output shaft, this is the strongest underdrive in the BlackBox lineup—designed...

northwestfab.com

Low range 1.96, 2.7 and about 5.33
A couple of other outfits do this.

 

[montechie]

Not surprising, weight plus too wide a rig doesn't make for a decent dirt road, much less an actual trail rig, that hog got slaughtered. What ER/EC/etc sells is an illusion of capability, the reality is that it's a fairly specialized rig that's too heavy, and too wide for much of the tighter Western US off-hwy roads. I'm sure they're awesome at rough terrain that's on flat, wide open terrain, but forget getting away from the crowds in the PNW and Mountain West with one on a 3+ rated route. That guy's lucky Trailmater serves that area, I bet most tow companies would've passed, not too mention 4x4 volunteer recovery clubs.

My wife and I considered EC or similar for a full-time rig, but it just wouldn't go where we currently like to go in the Western US and away from the crowds. The ERs/ECs/etc we often see around Bozeman land up camping in FS campgrounds or at the easy trailhead parking surrounded by Subies and regular RVs.

 

[DirtWhiskey]

I'm not aware of locking diffs...would be great to find a proven front/rear system designed for 550/5500: anyone out there doing this? Those tires appear to be Goodyear G275 335/80r20. Looking at the specs for those tires I have to wonder what newer/longer ER's weigh, especially the load on rear axle. The carbon fiber LTi is reportedly lighter than older models. I also note the speed rating is higher and ply rating is lower on the G275 than the MPT81. I seem to recall reading that Continental is revamping the MPT81 but don't have a link. Numerous folks using the G275 say that it is excellent for (US-made, modified chassis-truck camper level) offroad pursuits.

Super late reply. Missed your post somehow. There is no proper locker for the Dana S110 rear but it is LSD. The front is a wide track Super 60. Mine has 5.38 gears and a Yukon front locker. 2001 F450 converted to 2006 suspension and axles. Very capable.

 

[martinf]

Not surprising, weight plus too wide a rig doesn't make for a decent dirt road, much less an actual trail rig, that hog got slaughtered. What ER/EC/etc sells is an illusion of capability, the reality is that it's a fairly specialized rig that's too heavy, and too wide for much of the tighter Western US off-hwy roads. I'm sure they're awesome at rough terrain that's on flat, wide open terrain, but forget getting away from the crowds in the PNW and Mountain West with one on a 3+ rated route. That guy's lucky Trailmater serves that area, I bet most tow companies would've passed, not too mention 4x4 volunteer recovery clubs.

My wife and I considered EC or similar for a full-time rig, but it just wouldn't go where we currently like to go in the Western US and away from the crowds. The ERs/ECs/etc we often see around Bozeman land up camping in FS campgrounds or at the easy trailhead parking surrounded by Subies and regular RVs.

The EC, especially the EX with its smaller form factor is definitely a capable machine here in the PNW where it's built and tested. Sure it's not a modded Jeep but no RV is. There are many videos online of these rigs going places.

The ER is a different machine that is IMO too large and too heavy for anything less than large, no trees gravel roads. As much as I like the look of those rigs, it's mostly about having luxury while traveling rather than doing off-road traveling. The insulated house provides more comfort than a regular RV and the 4x4 helps with traction on snow covered roads and loose sand on the beach.

 

[bajajoaquin]

If your TC is one of the alloy chain-drive ones ubiquitous the last 20-25 years, it’s ~2.7:1. “Black box underdrive” is a short ~6” w/adapter gearbox that goes between transmission and transfer case. It’s only for trans/TC up to 350/3500 size vehicles. With a symmetric 6 bolt pattern between trans and TC. The 450/550 vehicles use a 8 bolt pattern.
What’s your vehicle?
If you have a F350, consider something like

Blackbox NP205 Titan

The Current BlackBox Build Time is 12 Weeks BlackBox TITAN – Strength Redefined The BlackBox Titan was built with one mission: unmatched strength. With a CNC-machined 6061-T6 billet aluminum case and a massive 1.75" output shaft, this is the strongest underdrive in the BlackBox lineup—designed...

northwestfab.com

Low range 1.96, 2.7 and about 5.33
A couple of other outfits do this.

I am coming out of the past, but missed this before. Yes, it’s a BW 1356 with about a 2.7 low ratio.

The chassis is an E450 so that’s a bit small. Thanks for laying it out for me, though.

 

[DzlToy]

My camper is no Earth Roamer, but I really feel what you mean about low gears. I’ve got a Dana 80 rear and ARB but only a 2.3:1 (I think) low range in my transfer case. With 4.63 gears, its just not low enough to be in the meat of my torque curve and still be at a walking pace.

This is the issue in 99% of trucks that are actually used off road. Everything from Sprinter vans to Fuso FG and everything in between, excluding a Unimog, which Charlie Aarons owns and uses, needs additional gearing to be safe off road.

I often hear, "I am not rock crawling, so I don't need low gears or even a transfer case at all. I have AWD and traction control." Utter Nonsense.

Go drive a properly-equipped vehicle with a REAL transfer case and at least 100:1 crawl ratio. (Transmission first gear x torque converter if so equipped, x transfer case low range x second low range, if so equipped x R/P ratio x portal end or planetary end, if so equipped. This number should be at least 100 for slow, technical work, off road. It isn't necessary that you are climbing Chocolate Thunder or Back Door in your EarthRoamer to benefit from low gears.

I have posted this video before and will post it here again to drive this incredibly important point, home to anyone and everyone who uses their truck off the pavement.

Notice the truck bounces and spins its tires at 54:1. This is how components break, wives and children scream and your truck slides off the road into a ditch. At much lower (numerically higher) crawl ratios, movement is controlled, no one is screaming, you have more time to react, talk to your spotter and can stop the vehicle quickly if things go pear-shaped.

 

[DirtWhiskey]

This is the issue in 99% of trucks that are actually used off road. Everything from Sprinter vans to Fuso FG and everything in between, excluding a Unimog, which Charlie Aarons owns and uses, needs additional gearing to be safe off road.

I often hear, "I am not rock crawling, so I don't need low gears or even a transfer case at all. I have AWD and traction control."

Go drive a properly-equipped vehicle with a REAL transfer case and at least 100:1 crawl ratio. (Transmission first gear x torque converter if so equipped, x transfer case low range x second low range, if so equipped x R/P ratio x portal end or planetary end, if so equipped. This number should be at least 100 for slow, technical work, off road. It isn't necessary that you are climbing Chocolate Thunder or Back Door in your EarthRoamer to benefit from low gears.

I have posted this video before and will post it here again to drive this incredibly important point, home to anyone and everyone who uses their truck off the pavement.

Notice the truck bounces and spins its tires at 54:1. This is how components break, wives and children scream and your truck slides off the road into a ditch. At much lower (numerically higher) crawl ratios, movement is controlled, no one is screaming, you have more time to react, talk to your spotter and can stop the vehicle quickly if things go pear-shaped.

Bingo. Why I put in 5.38 gears in my F450 rig. I'm at about 2200 rpm at 65 but I don't like to go faster than 70mph (plenty fast) on those MPT81s. Crawl ratio is good, but could be even better. Becomes much more important (along with LSD rear and front locker) on bigger rigs with real weight. Takes a lot of pressure off the drive line components and everything else. Slow is good, momentum is bad in that situation.