Earthroamer Tires

[charlieaarons]

Also, the tires on the Fuso are 325/85R16 XMLs, not 335/80R20 (which comes only in XZL).
38.7" tall instead of 40.7".
A picture of Turtle 5 shows the 335/80R20 XZLs. Which have a lower load rating than the MPT81s (141K, or 5780 lb@ 62 psi @ 65 mph).

Charlie

 

[JRhetts]

Axel ratio for 41" Tires

I am seriously contemplating going for MPT 81 tires on my new ER.

Objectively, what are the wear-and-tear and performance issues if I stay with the standard 4.88 rear end. I understand that going from 37" to 41" tires with the same rear end will - to "some" extent - reduce low end acceleration as well as higher speed rpm/mph (slightly increase mpg).

What other consequences are there? How significant?

Thanks, John

 

[haven]

Switching to 41 inch tires will be like driving the 37 inch tires without a 1st gear. The 41 inch tires are likely to be heavier than the 37 inch, which will take its toll on brakes.

Here's the Turtle V with 20 inch Michelins

 

[charlieaarons]

The ratio increase from 4.30 to 4.88 exactly compensates for the diameter increase from 37.0 to 40.7; actually with 1% to spare. However, I'd be a little concerned about the front axle. If you were to call Dynatrac they could tell you all sorts of things about the Dana Super 60 unit bearing front axle, in the process of trying to sell you something of course.
In the rockcrawling world (very high stresses but low weights) a Dana 60 is considered adequate up to ~40"; you see a shift to Rockwell 2.5 ton axles above that size. You'd be running at least twice the weight of a modified 4X4 rockcrawler on the front axle of an ER (6000 lb vs. 2-3000). But of course not stressing things as much as a rockcrawler.
Modifications to the front axle you might at least consider:
conversion to spindle/adjustable wheel bearing setup
35 spline outers (the Super 60 may already have that)
Maximum strength U-joints between inner and outer axleshafts
strongest possible freewheeling hubs
some kind of axle housing beef-up.

The rear axle hopefully will be fine since it's designed for duals already.
Of course if one could track down Gary Westcott you could ask him if there have been any front axle troubles.

Charlie

 

[saltamontes]

interesting observation that the toyo MT's are overheating on the ER.
curious to know speed, psi, load and temps seen as i am considering these tires for my F350 SRW w/ NLite camper.

for those of us running relatively higher loads/low pressure/washboards@35mph, it would be great to find a chart showing load-rating and safe speed so we can know that a tire w/ load n can run at low pressure x for speed y before delamination becomes a concern.

this thread seems to be covering 5-6k/tire (10-12k rear axle) capacity.
The Turtle5 looks to be much lighter that the ER. Heck, it looks to be much lighter than even my 2,300 lb (dry) cab-over.
Anyone have measured real-world weights of a loaded ER or Turtle5?


Someone mentioned looking for Alcoa forged 20" aluminum wheels for Ford SRW.
My understanding is that Alcoa has been doing the forging for the stock 20" and 18" aluminum wheels on the F250/350 superduty for years. Granted, their capacity is only 3600+lbs/ea, but that should be plenty for most campers on a SRW meant for offroading (not too many (except the ER folks) are boonie bashing their 1191 lance)

Re. 19.5 Ricksons and camper, there is a ton of info over at rv.net

 

[boblynch]

If I'm following you guys it boils down these questions.

1. What is the difference in weight between the wheel/tire OEM setup (225/70R19.5), the current ER setup (295/60R22.5), and the new setup (335/80R20 MPT81)? The increase in rotational mass will impact the wear and tear on parts.

2. What spacers and/or modifications are required to get the new wheel setup to work? Does this cause any unexpected issues?

3. What is the handling impact of the 3" lift needed to move up from 37" to 41" tires?

 

[JRhetts]

Bob
I think your questions help get at the core of the matter for me. Specifically...

If I'm following you guys it boils down these questions.

1. What is the difference in weight between the wheel/tire OEM setup (225/70R19.5), the current ER setup (295/60R22.5), and the new setup (335/80R20 MPT81)? The increase in rotational mass will impact the wear and tear on parts.

From initial prototypes, the 20"rim with 335/80R20 will be slightly lighter that the current 22.5" 295/60 Michelins. This is in no small part due to not needing the steel adapter plate and second set of 10 lugs and nuts. However, I would guess(!) the rotational mass might be increased, due to the larger diameter and more rubber in the tire (bigger fulcrum and more weight farther our on the lever).
My real question is: will the impact be a "functionally significant" increase in wear and tear?

2. What spacers and/or modifications are required to get the new wheel setup to work? Does this cause any unexpected issues?

So far as I have experienced and heard re: other owners, the existing adapter plate has not caused any issues. The new set up would not require any adapter at all.

3. What is the handling impact of the 3" lift needed to move up from 37" to 41" tires?

I have been informed that one ER owner has done a 3-4 inch lift on his own; the handling with the 22.5 set up is reported to be essentially unchanged. Another owner installed 4-point airbags; his handling in his opinion is significantly improved.

Charlie- how hard/expensive might the front axle mods you described be? Given that they "could" be done, how realistically important would they be?

John

 

[charlieaarons]

Bob



From initial prototypes, the 20"rim with 335/80R20 will be slightly lighter that the current 22.5" 295/60 Michelins. This is in no small part due to not needing the steel adapter plate and second set of 10 lugs and nuts. However, I would guess(!) the rotational mass might be increased, due to the larger diameter and more rubber in the tire (bigger fulcrum and more weight farther our on the lever).
My real question is: will the impact be a "functionally significant" increase in wear and tear?


Charlie- how hard/expensive might the front axle mods you described be? Given that they "could" be done, how realistically important would they be?

John

Yes, it's a matter of angular momentum and leverage, in addition to weight.
The front axle mods would be "relatively" easy to do. As far as necessity, it's hard to know. I do feel 40-41" is the borderline of the reliability zone for a heavily loaded Dana 60. There are many opinions on this I am sure. Like I said, Dynatrac could paint you the "worst case scenario". And suggest upgrades. I don't even know if changing from a unit bearing to spindles increases reliability. It does increase serviceability, at the cost of increased maintenance (tightening wheel bearing nuts, repacking bearings).
I can say without much doubt you want 35 spline outers (may come with the axle), killer U-joints and strongest possible hubs.

Charlie

Charlie