Off-roading Performance -- a comparative technique

Diffs, axles, lockers, transmissions, portals, that kind of thing.
Post Reply
User avatar
rmel
United States of America
Posts: 892
Joined: Sun Sep 25, 2011 12:19 pm
Location: Woodside, CA
Contact:

Off-roading Performance -- a comparative technique

Post by rmel » Fri Oct 27, 2017 12:52 pm

As a warning, this is going to be long, possibly controversial, and geeky. Essentially I have come up with a way to graphically
compare off-road capability using key specification data. Scroll down to the chart and see if this looks interesting to you. I did
this research for myself, then thought some would find it useful. Just to be clear this is one way to look at capability and
certainly not the only important factor -- it did help me to put things in perspective. All this analysis is predominately 4x4,
Manual tranie's, torque converters are different. Typically rigs are 70's and 80's era. If you see something wrong with my
data provide me source data and I'll make corrections. Now the background ---

I bought my 710K with a TD Tranie + 2.7L/EFI, it's all I know. For me trails worth wheeling to are 200+ miles away, the
improved HWY performance is a plus. Although, after a very challenging run to Snake Lake in the Sierra's I decided to
revisit the Pinz drive train options. There are mixed reviews of the TD Tranie in the 1'st gen Pinz, some say it's a bad idea.
viewtopic.php?f=13&t=10003

First gear in the stock Tranie is 5.33:1, the TD is 4.25:1 that put's TD's 1'st gear between 1'st and 2'nd of the stock Tranie
and a 25% reduction in applied Torque -- as a spoiler an Engine upgrade has to be part of any move to taller gearing or you
will absolutely regret it. Even if the percentage of Torque gain from the 2.7L engine upgrade were to equal the gear ratio loss
it will NOT completely compensate for the difference, this is will become obvious.

I started thinking about a technical way to graphically compare the Pinz drive train options relative to each other and against
other rigs based on "wheeling" factors. I could not find anything published that represents this idea. What I came up with is based
on a fundamental principle -- moving a heavy mass with control over obstacles up steep grades. The first factor is, Force to
Weight Ratio (FWR), obviously important for any 4x4 facing steep grades. Calculated using total gear ratio, Tire size, Engine Torque,
and Curb weight, it's simple to calculate. With FWR=1.0, ground force equals vehicle weight. In theory, you could crank your truck
up a vertical wall. However, FWR=0.5 implies a grade limit of 30 degrees. FWR is the Vertical axis on my chart. The other factor,
Ground speed, measured in ft/sec. This is a measure of control. Fast presents less control negotiating obstacles, hitting an obstacle
too fast, or breaking traction on a steep grade. Slow is better, more latitude to reach peak torque from a dead stop. Calculated from
Total gear ratio, Tire size, and at a fixed RPM of 2,000. This becomes the horizontal axis. I picked 2,000 RPM as a baseline as that
is a fairly common RPM near peak torque, below 2,000 many engines have a sharp roll-off in Torque.

Trucks compared; 710 and various drive train options, 712 stock, Mog 404, C303, 716, CJ-7, Hafie, Series III, FJ Crusier, FJ40,
1979 G-461/280GE, VW Thing 181s with Portals, and for yuks a Mini-Cooper. The CJ-7 is factory with aggressive options, I also
show a lifted CJ-7 with 37" Tires and Dana 4:1 X-case. A Table with the data is included. In the table you can see why some look
for taller gears. A stock Pinz 710 is 3800 RPM @ 60 MPH, high rev's for the Mog and C303 as well. If not the extra work on the engine,
these Rev's are very noisy. This has lead to the TD Tranie swaps in the 710 where 5'th is OD now your down to about 2700 RPM at 60.

For tire diameters I assume nominal. For example a 285/75R16 = 32.8" but under load at 45PSI it's close to an effective 32", so I
assume 32" for 16" wheels, and 30" for 15" wheels etc.

Pinz options, TD Tranie swap, swap 712/710 X-cases, and Engine upgrade. I made up pseudo Model numbers:
710-TG-X10 = Stock 710, TG is stock Transmission Gas, and stock X-case
710-TG-X10-EFI = Same as above with 2.7L Engine conversion, a 20%+ Torque boost.
710-TD-X12 = 710 with TD Turbo Diesel Tranie, and 712 X-case
710-TD-X12-EFI = same as above with 2.7L Engine conversion
710-TD-X10 = 710 with TD Tranie, stock X-case
710-TD-X10-EFI = same as above with 2.7L Engine conversion

Before jumping to the results, there a few properties of this chart to understand. First as a broad observation, Rock Crawlers
are in the upper left quadrant of the chart, with high FWR and low ground speed. Passenger vehicles would be are in the
lower right, low FWR high ground speed. Military/all-terrain are in the middle, but with FWR>1 and ground speed typically < 6 ft/sec.
The question is, when the gearing is changed, what happens to a specific Vehicle. It's pretty obvious that increasing gear ratio
increases FWR and slows the rig down. Changing gears and/or tire size results in a given point on the chart moving in a straight
diagonal line. This is an important point as relative performance gains with gears or tires is basically a square law effect -- increased
gearing moves to the left and up. Changing Torque, or Curb weight moves up/down the vertically axis only. This is why when you
swap in a TD Tranie even with the Engine improvement you end with a compromise in off-road capability, the Torque gain didn't fully
compensate. And without the Torque boost, you are much worse off.

On the chart are all three variants of drive train options for the Pinz both with and without the Engine upgrade are shown. The
stock Pinz is FWR=1.35, at 4.8 ft/sec, compared with the TD with EFI the original equipment is simply better off-roading performance.
Although with the TD+EFI it's still better than a Series-III. Given a choice, the TD+712 X-case with EFI would be better balanced but
major surgery. The stock Pinz, C303, and G-461/280GE are very closely matched. The 716 is a major improvement over the original
Pinz. Then there's the little Hafie and shows it's quit capable. The FJ Cruiser is a significant improvement over the FJ40 which was
geared too tall, a rear diff change would make a significant improvement and some have gone this route. The Mog 404, with a FWR = 4.0
and speed of 1 ft/sec, you can see why they are great rock crawlers. From what I determined true crawlers have a FWR >3 and
move <3 ft/sec. A lifted CJ-7 with a 37" tires and a Dana 4:1 X-case has a FWR=5 and 3 ft/sec. A brief note on the 712 -- lower
gearing didn't totally make up for the additional 1,000 lbs of curb weight against the 710, but they are pretty equivalent only due to the
slower ground speed, the 712 with EFI would put the 712 closer to Pinz diagonal line. As far as drive train options for the 712, the
best trade-off would be a swap to the 710 X-case, the TD tranie in the 712 is approximately the same trade-off as the TD in the 710
even with the 712 X-case due to the higher curb weight, goes without saying EFI is a must.

My conclusion at this point is that a Pinz is not a Rock Crawler though they are very capable vehicles, the TD tranie even with a big
bump in Torque is a definite compromise but, from my experience still capable. I have no immediate plans to swap out the TD tranie,
again as I spend a lot of time on HWY. However, now with a method for comparison I plan on going down somewhat in tire size to add
an additional 5% in FWR and 5% reduced ground speed, airing down is also a big help reducing effective Tire diameter. I also now
know my Pinz's limitations better and when to turn around. If a 712 X-case shows up one day, I'll consider moving in that direction.
I enjoyed digging up all the data. I hope you find this interesting and helpful.
Crawl-Chart.jpeg
Crawl-Chart.jpeg (257.8 KiB) Viewed 1249 times
Crawl-Table.jpeg
Crawl-Table.jpeg (379.14 KiB) Viewed 1214 times
Last edited by rmel on Fri Oct 27, 2017 7:53 pm, edited 1 time in total.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

User avatar
VinceAtReal4x4s
Admin
United States of America
Posts: 1658
Joined: Mon Apr 12, 2004 10:36 pm
Location: Ca. or lost in South West USA
Contact:

Re: Off-roading Performance -- a comparative technique

Post by VinceAtReal4x4s » Fri Oct 27, 2017 1:21 pm

Wow impressive work. Did you get really bored at work recently? :)

I like how the Unimog is way out there by itself. It might be fun to add a 416/AG. Mog to the graph with its 4000:1 Cascade gears.

For the layman or newbie I think it's important to add that this is a very narrow part of the "ability" spectrum being referred to and in no way reflects actual, overall off-road capability of any certain vehicle. What this is referring to is essentially the ability to control speed/power to the tires when in the lowest gear, which is most often needed when facing difficult, off-set rocky terrain, but even then comparing real-world ability becomes very complex, even on paper.

There are, for example, situations where even the FJ40 which is seen way to the right on the chart, could concur a common obstacle the Mog would have a lot more problems with, such as a small sand dune or steep muddy switch-back.
"For those who risk, life has a flavor the protected shall never enjoy"

Real4x4 Facebook https://www.facebook.com/real4x4s

Image

User avatar
TechMOGogy
Canada
Posts: 2788
Joined: Wed Feb 01, 2012 11:39 am
Location: Ontario, Canada

Re: Off-roading Performance -- a comparative technique

Post by TechMOGogy » Fri Oct 27, 2017 1:46 pm

Hafi at 60mph - now thats funny!
The Hafi actually does quite well in your chart
Neat read and chart!
Thx for sharing

I also think the specs for the 404 LL is if your using 1st gear in the 2 speed crawler gears (they were optional)
Regular 1st should 112.87 @4800rpm
http://www.rockymountainmoggers.com/gears.html
Last edited by TechMOGogy on Fri Oct 27, 2017 2:04 pm, edited 3 times in total.
72 Pathfinder | 75 710M 2.7i | 96 350GDT Worker

Heinkeljb
Great Britain
Posts: 353
Joined: Wed Feb 27, 2013 1:09 pm
Location: Lewes,Southern England

Re: Off-roading Performance -- a comparative technique

Post by Heinkeljb » Fri Oct 27, 2017 1:52 pm

Query on your data table:-

The Mini apparently has 12 inch tyres and Haflinger has 24 inch? Neither are true of rim size, Possible true for the Haf as wheel diameter, but definitely nor true of the Mini wheel diameter.
Does correcting this erro make any difference to the position of the Mini in your graph?

John

User avatar
rmel
United States of America
Posts: 892
Joined: Sun Sep 25, 2011 12:19 pm
Location: Woodside, CA
Contact:

Re: Off-roading Performance -- a comparative technique

Post by rmel » Fri Oct 27, 2017 3:16 pm

Hey Vince, no didn't get bored at work but I sure wanted to get a
better than a gut feeling for my 710 config, which this did :wink:

Dan I got the data for the 404 off of rockymountain mogers :)

Typo on the chart for the mini, won't change the results any, I;ll
clean that up later after perhaps a few more comments come rolling in.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

User avatar
Jimm391730
United States of America
Posts: 1456
Joined: Wed Apr 14, 2004 10:58 pm
Location: Idyllwild, CA

Re: Off-roading Performance -- a comparative technique

Post by Jimm391730 » Fri Oct 27, 2017 4:26 pm

Nice work. Just a thought: airing down does not really change the tire radius - you still have the same circumference of tread to go around each revolution (this is why tire speed is no longer allowed as a method of determining under pressure in tires - the rotational speed is almost exactly the same). HOWEVER, if an aired down tire goes over a bump that is a sharp "point" that pushes the tread up close to the rim, there is some brief reduction in radius that happens. A similar thing happens if the tire is NOT aired down, since the distance that the tire travels is no longer straight but includes up/down portions that slightly reduce the distance that one tire rotation would otherwise go on flat ground. The aired-down tire just doesn't go up and down over the sharp obstacle as much since the obstacle can push into the tire instead of the tire rising up over it.

This is a total Geek-out, but I have thought about aired-up/aired-down differences and there is almost no difference between them. Obviously, aired-down gives a softer ride and improves flotation and grip, but distance traveled in one rotation is still effectively the same (less than one or two percent change).
Jim M.
712W and 710M

User avatar
rmel
United States of America
Posts: 892
Joined: Sun Sep 25, 2011 12:19 pm
Location: Woodside, CA
Contact:

Re: Off-roading Performance -- a comparative technique

Post by rmel » Fri Oct 27, 2017 7:16 pm

Jim, not so. Airing down reduces the effective tire radius and slows you down.
In fact normal tire pressure has a reduced tire radius less than the unloaded tire.
The speed of the wheel Omega, is determined by the point of contact from ground
to the center hub of the wheel. And that will be slower than the spec diameter
of the tire. There is a fair amount of data out there on this. See here.
https://www.tut.fi/ms/muo/vert/11_tyre_ ... radius.htm
There is also a rolling radius that is a more accurate representation of the effective radius but
that's a very complicated as it is load and velocity dependant, see here.
https://www.iaea.org/inis/collection/NC ... 052898.pdf

You may not be able to measure the difference aired up or down, we are talking about a 5 to 7%
difference but I'll take that as it is a square law thing.

cheers,
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

User avatar
rmel
United States of America
Posts: 892
Joined: Sun Sep 25, 2011 12:19 pm
Location: Woodside, CA
Contact:

Re: Off-roading Performance -- a comparative technique

Post by rmel » Fri Oct 27, 2017 8:01 pm

Dan, BTW a 404 without the 1'st crawler option would put is pretty close to the Hafie :)
That's be one kick Eh !
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

User avatar
TechMOGogy
Canada
Posts: 2788
Joined: Wed Feb 01, 2012 11:39 am
Location: Ontario, Canada

Re: Off-roading Performance -- a comparative technique

Post by TechMOGogy » Fri Oct 27, 2017 8:51 pm

rmel wrote:Dan, BTW a 404 without the 1'st crawler option would put is pretty close to the Hafie :)
That's be one kick Eh !
Thanks for that update!
Hafi’s Are pretty amazing little machines and a real blast to drive (think go-cart)
72 Pathfinder | 75 710M 2.7i | 96 350GDT Worker

User avatar
rmel
United States of America
Posts: 892
Joined: Sun Sep 25, 2011 12:19 pm
Location: Woodside, CA
Contact:

Re: Off-roading Performance -- a comparative technique

Post by rmel » Mon Jan 15, 2018 8:05 pm

I have intended to respond to Jim's point that airing down does not significantly reduce a Tires effective radius.
Just got some time today to make some measurements, the results are surprising -- to me at least :wink:

Initial tire pressure 50 lbs, measured tire radius center of hub to ground 15 5/8", unloaded radius 16 1/4".
Aired down Tire pressure 19 lbs, measured tire radius center of hub to ground 14 3/4".
One other measurement made was the Tire radius from center of hub to the edge of the ground contract
area, that's the part of the tire that is "just touching the ground. Ha! This was almost exactly the same at
both tire pressures at 16 1/8" -- this is VERY interesting -- more later.

So I chalked ground, rolled forward 2 tire revolutions at 50 psi, aired down, then rolled back 2 tire rev's
and low and behold I expect to see 6" LESS travel in the reverse direction due to a smaller effective radius.
What I measured was 2" or 1" less per/rev for 50 vs 19 psi. What the heck :?:

So this does confirm that lower tire pressure does not make a significant difference in Torque, but for sure
a significant increase on traction and "bounce" control. There is some torque increase BUT far less than
expected and far less than reducing the size of your tire. It' just darn interesting.

I did find articles that does confirm this but these papers where for passenger cars with low profile tires.
But it was suggestive that Radials limit the expected tire radius reduction vs pressure while bias ply tends
to be much closer to expected. IT's the steel cords that does it, it's a pretty strong spring -- so to speak.
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

User avatar
rmel
United States of America
Posts: 892
Joined: Sun Sep 25, 2011 12:19 pm
Location: Woodside, CA
Contact:

Re: Off-roading Performance -- a comparative technique

Post by rmel » Mon Dec 10, 2018 7:09 pm

It's been a bit over a year now since I did this analysis. One conclusion I had
made was that the TD tranie in a 710 is bad trade off for off-roading and
certainly terrible if your running the lower power (Torque) unmodified engine.
I stand by that position.

This past spring I decided to fix this problem with what I believe to be the best of
all compromises -- a 712 transfer case mated to this TD tranie. I managed to source
a 712 X-case and just completed this surgery.

On the HWY, the TD's 5'th gear is over-drive, RPM was 3150 @ 60MPH on 265/75 tires.
A stock Pinz is approximately 3600 RPM @ 60MPH. This seems like a decent trade-off
to me. I was also able to stay in 5'th longer than before even with grade.

On the trail, my only test is a old logging road on my property, not that severe or long
enough to render a full impression, but I can tell that there is a huge difference in
crawling performance and Power. Can't wait for spring to hit the trails.

PIX of disassembled drive-line ready for re-assembly attached.

As a passing comment, this was a fairly big project and is definitely a 2 man job.
There are several techniques and procedures you have to know to attempt this, but it's
a doable project. Proper jacks/lifts and a good life insurance policy is recommended :wink:
IMG_1890.jpg
IMG_1890.jpg (897.96 KiB) Viewed 379 times
Puller: 71' 710K 2.7L EFI aka Mozo
Follower: Sankey MK 3, 3/4 Tonne
Rescue Pinz: 73' 712M

Driver: Ron // KO0Q

Post Reply