Suspension Design Tutorial

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Date: Sun, 24 May 1998 05:15:08 EST
From: "james stevenson" 
Subject: Re: Leaf spring alternatives

Sorry all but can see this going to get long

Jon Brandt Wrote (clipped)
>Why won't IFS "articulate"? ......why it wouldn't be able to use its
>travel independently, after all it is independent suspension. ......I
>agree that a-arm suspension is way limited for travel. But, trailing
>swing arms can offer alot of travel...... With IS, if you have travel,
>you have articulation, its already independent to move as far as it
>can without being affected by the other wheels.

John I think you misread what I wrote "difference between the IFS/Coil 
Rear trucks and the Leaf sprung solids, The IFS has travel where the 
solids  have articulation" This referred to the Toyota Pickup type IFS 
Vs the Solid Axle version. Not all possible suspension designs on all 
trucks  I also wrote that that VW rear (Trailing arm) had Travel not 
articulation.  

Travel and Articulation are two very different things. Put simply Travel 
is when both wheels move together in the same direction and articulation 
is when they move in opposing directions. This does not change with IFS, 
but is often confused. No suspension is truly independent due to a thing 
called unsprung weight, as well as shocks, swaybars, etc.. Unsprung weight 
is the weight of all the components that move in relation to the 
suspension. Unsprung weight is why Indy and F1 cars have brakes and coil 
overs mounted inboard. If the IFS has relatively no unsprung weight in 
relation to sprung weight you can lift a wheel to the top bumpstop 
before you induce force on any other wheel, assuming the shocks and 
spring are correctly matched and you don't have swaybars. But this does 
not change the travel or articulation. It does, however, provide a softer 
ride. Due to shocks, springs, and swaybar imposing force on the frame, IFS 
does induce reactions in the opposing wheel, granted much less than in 
Solid axle designs. With all radius arm setups, including trailing arms, 
this is a disadvantage, but it is an advantage in leaf spring setups. 

Regardless of the suspension mounting, the suspension must pivot on some 
kind of arm.  In the leaf spring setup, arm is from the fixed spring eye 
to the axle. The IFS has a much shorter arm, therefor, the travel is much 
less. The Trailing arm type setup allows for a much longer arm and 
therefor more travel. This setup is used well in the LC 60-80 series.

All suspension systems have limits, the IFS is limited by the distance 
it can go up, which is why you relocate it down for more travel. But this 
is only removing limitations in the Toyota design, to really increase 
travel you have to increase the arm length.  

Trailing arms introduce articulation problems in that the axle also 
travels at an arc set by the distance between the arms. This means the 
arms must twist, and this ability is limited by the axle mounting method 
as it needs to be secure. As the axle moves down, it arcs closer to the 
arm mount. With articulation the same wheel moves closer to the frame 
centre. This creates a problem in the arms as the articulation increases 
from the at rest position. This a major reason that the trailing arm 
setups tend to rip out the mounts. It is also exasperated by the upper 
arms in that they are mounted away from the axle centre which creates 
the need for the panhard rod and travel through a different arc to the 
lower arms.  This is basically a cost issue in that improved mounts 
increase vehicle cost. Compare the Toy setup to the Land Rover rear end 
on the Disco, 90, 110 or Rangie which is an excellent example of a rear 4 
link. For the trailing arm setup to offer more articulation, you have to 
lengthen the arms, and or, move the frame mount closer to the frame 
centre. In the case of the Toyota rear setup, it is also limited by the 
up travel on the arms, in that they have unequal up and down travel, 
again moving the mounts down improves the limitations but does not 
change the way it moves.

Leaf springs pivot on the fixed eye which creates the travel. Like on
radius arm or trailing arm setups, leaf springs need to twist for 
articulation. As they are made from spring steel and have generally much 
more movement in the bushings, articulation is not limited to anywhere the 
same extent as the trailing arm setups. Since leaf springs have arch, as 
the spring moves, the length of the spring changes. This gets around the 
mount problems seen in trailing arm setups. But the Leaf spring has a 
problem with travel, in that the spring is also connected to the frame 
(via the shackle). This connection being separate, the radius arm will 
always limit the travel. Added to that, leaf springs provide progressive 
spring rates in two directions, as differentiated from a coil setup that 
is always acting to push down on the wheel. A leaf spring will also pull 
it back up. This limits the travel but increases the articulation. When 
one wheel moves up, it forces the opposite wheel down. This creates the 
extra force needed to extend the spring beyond the free arch. Where 
travel is concerned, there is no force extending the spring beyond the 
free arch.  This is the prime reason why the leaf setup articulates more 
than it travels. Unlike the other setups, more travel is easily gained with 
springs that have more arch and less rate. As with the other setups, to 
increase the articulation a longer arm is needed, this is where the 
longer spring setups come in. Also, changing the spring to full elliptic 
removes the shackle limitation and adds more articulation. Added to this 
is that the pivot points on a leaf spring setup can be moveable which is 
generally not possible in the other designs. This is the concept behind 
the buggy spring and double jointed shackle or missing link setup, 
having a multiplying effect on the articulation, and a direct increase 
in the travel. 

If you compare the three setups in the Toyota Pickups and 4 runners The 
longest suspension arm radius arc is the Leaf spring setup, followed by 
the trailing arm setup, and then the IFS. Without changing these factors 
the articulation will come in leaf, trailing arm, and IFS while travel 
is trailing arm, IFS, then leaf. My new truck uses IFS front and rear and 
has way more travel and articulation than my solid. However its been 
made from scratch that way, and does not use the Toyota setup. In effect 
I have longer arms, less unsprung weight and equal up and down travel.
The wheels are also specially offset to increase the length of the arms. 
To get the up travel I had to locate the pivot points about 12 inches 
lower that normal and offset the wheel down using hummer geared wheel 
hubs. I considered a few other designs for the suspension such as 
maximum length radius arms. Such that the front and rear arms were 
mounted at the same point, or being half the wheelbase long. As well as 
a leaf setup and a 3 link coil setup both of which provided more 
articulation and travel than the IFS. However I went with the IFS for 
other reasons deciding that the IFS had enough to do the job.  

So I'll say again "Comes down to having the right tool for the job in 
the kind of stuff you drive in" go for the articulation if you need to 
crawl in the rough stuff, and travel if your wheeling is done over the 
dunes, desert or dirt roads.

James Stevenson (TonkaTuf)

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Date: Sun, 24 May 1998 12:54:59 -0700 (PDT)
From: Jon Brandt 
Subject: IRS was: Leaf spring alt.

I think we both misunderstood. My mistake was to use the term IFS in the 
first sentence; there after I used the term IRS (independent rear 
suspension). This is because IFS was seemingly being used to describe 
independent suspension in general. I was refering to rear suspension 
ONLY. That's why I refered to  the IRS of the VW bug-based buggies.

I apologise now for any greif this miscommunication may have caused.

Everything James has written is correct. 
To clear up the misunderstanding I will start by saying that I meant rear 
suspension. I meant to state that the idependent suspension design used 
in the front of toys (a-arm IFS) is clearly limited. BUT, a swing-arm 
design clearly can offer alot of travel. Travel and articulation ARE 
different, but independent travel can equal either. When I talk about a 
custom set-up I should be allowed the assumption that sway bars will not 
be used if the purpose of the suspension is to achieve articulation. As 
for shocks...well everybody's gott'a use'm. All of this is theoretical, 
because, again I've never seen anybody use IRS for rock crawling. 
Actually, I take that back, I have seen a Volkswagon based buggy on a 
trail, but of course it was not four wheel drive. It did appear to be 
doing much better than many 4WDs (had to have at least a limited slip), 
considering it's high gearing as well, and yes the rear was articulating 
very well.

My origonal point was: If you have an IRS (independent rear 
suspension) set-up with, say 24" of travel, and the suspension is by 
design independent (each wheel can move completely through its travel 
without affecting the others, other than through weight distribution), 
then why couldn't it "articulate" completely? The answer is, there is 
nothing stoping it. If it must be compared to leaf springs, then in this 
case it does not have the binding action of leaf friction and twisting. 
This is not to mention the angles that the tires would be at.

thanks for the discussion to clear things up.

------------------------------------

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Date: Tue, 26 May 1998 18:33:45 -0700 (PDT)
From: Jon Brandt 
Subject: Re: IRS was: Leaf spring alt.

On Mon, 25 May 1998, Scott Ellinger wrote:

[clip]
> > I understand this now, but why can't it articulate?
> > 
>I think this subject was hashed out a while back on the off-road list, and
>the consensus was that articulation was the relative angle of an axle 
>housing to the frame (or one part of the frame to another, in the case of
>articulated frames) and travel was the simple vertical distance available
>to a given wheel for movement.
> 
>What it boils down to is that an independent suspension, while perhaps very
>capable of massive travel, is unable to articulate, because it doesn't 
>twist the axle housing (center in the case of independent) on the frame.
> 
>Articulation is really just a subset of travel, when you get down to it.
>If you have articulation, you have travel, but not necessarily vice versa.
> 
> --scott
> Scott Ellinger   ellinger@holly.colostate.edu   Larimer County 4WD Club
>         Visit my Home Page: http://holly.colostate.edu/~ellinger
>  '86 Toy pickup body, Ford 5.0, GMC NV4500, "slightly altered" RKSTMPR
> 
> ============================================================================
> Toyota 4x4 page: http://www.off-road.com/4x4web/toyota
> 

Now I understand...It was a misunderstanding of terminology/definition.
Thanks Scott...
In that case articulation is not neccessarilly a good thing. Massive 
independent travel would be ideal. The tires arguably have more traction 
when their surface is closest to perpendicular to the force of gravity. 
The vehicle is most stable when it is the same. Even on a sloped surface, 
an aired-down tire would LIKELY get better bite being closer to verticle, 
than if it was articulated (toed), due to contact pressure. (The 
difference is probably negligable, and solid set-ups are much cheaper, 
and that's part of the fun.) But again this has not been proven, and I 
don't believe it will be, one way or the other, in the near future. 
Unless...I think the only person who could enlighten this subject with 
authority would be James Stevenson. Have you taken your rig rock 
crawling lately? 

O.K., I've beat it down, but if you've read this far and are not 
interested...

Jon Brandt
Sacramento CA, '86 Turbo 4Runner


============================================================================
Toyota 4x4 page: http://www.off-road.com/4x4web/toyota

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Date: Wed, 27 May 1998 23:17:34 EST
From: "james stevenson" 
Subject: IRS was: Leaf spring alt.

>If you have an IRS (independent rear  suspension) set-up with, say 
>24" of travel, and the suspension is by design independent (each
>wheel can move completely through its travel without affecting the
>others, other than through weight distribution),  then why couldn't it
>"articulate" completely? The answer is, there is nothing stoping it. 
>If it must be compared to leaf springs, then in this case it does not
>have the binding action of leaf friction and twisting. This is not to
>mention the angles that the tires would be at.

Jeez, quite a few things there. 
You are correct in that a solid axle design must change camber with 
articulation. Usually this is not a consideration I look at, for the 
reasons that on road these changes are within acceptable limits and off 
road (with aired down tyres) these camber change is taken up by 
deformation of the sidewalls and not a concern. As for the binding and 
twisting in leaf sprung setup they are actually advantages compared with 
the other setups. The friction helps in absorbing oscillations in the 
same way as a shock does. This is why you can run softer shocks with 
leaf springs as compared to coils and torsion bars. The twist is what 
allows the additional articulation over 4 link types setups in that it 
can be forced past its static position where a fixed length arm will not 
allow this (or rips out a mount). 

You can have independent suspension with arms either laterally as in the 
Toy A arm setup or in parallel to the frame as in a trailing arm setup 
(Subaru wagons). With both types you are limited to the driveshaft 
angles, however I will assume we are talking setting the arms laterally. 
You are correct in that the independent system can articulate 
completely. But this does not mean anywhere near a solid axle setup be 
it a trailing arm, 4 link, leaf spring etc. And the reason is 
driveshaft angles. 

To explain lets assume we are installing a custom made rear end in a Toy 
Pickup.  Exact frame measurements will vary with the gen of the pickup 
and the wheelbase but lets assume the frame is 47 in wide and the 
transfer flange to the diff flange is 60 inch (down the frame). If we 
look at the IRS setup first we need to fit in the pumpkin and brakes 
which limit the length of the arm. To get the maximum length of the arm 
we will put the brakes out on the hub and not inboard. So the length of 
the arm will be half of the width of the frame width less half of the 
diff width. Say we get the diff down to 11 inch wide that would mean a 18 
inch long arm. An 18 inch arm that moves 30 degrees up and down will 
have an 11 inch movement or 22 inch travel.  This will also mean the diff 
is to be fixed about 25 inch below the frame to allow the up travel and 
to clear the tyres. As for a solid axle setup we have no driveshaft 
problems with articulation but have a travel problem with the angles. We 
are also limited to moving the shaft down only relative to the Tcase. So 
a 30 degree movement of the tailshaft (CV's installed and 60 inch long) 
is about 75 inch of possible travel. By placing the suspension linkages 
up at the Tcase this kind of travel is within the limits of the arms, but 
articulation will be limited by the centre of gravity as we can't have 
the axle 75 inch down from the frame at rest. We are assuming a toy 
pickup so lets say the maximum the axle can sit down from the frame at 
rest is 20 inch. Given the right linkages we will then have articulation 
of 40 inch. If we say a practical limitation is also a 45 degree 
limitation on the axle we still get over 40 inch. So a solid's 
articulation all depends on the limitations of the linkages which is why 
I wrote earlier "Travel is easy but articulation is hard", but clearly 
far more travel and articulation than the independent designs within the 
same frame. Going for broke I'd eliminate the tyre clearance problems by 
articulating the frame behind the cab and provide a limited articulation 
suspension in the rear frame something like a trailing arm but with max 
travel on airbags set close to the pivot on the arms and lock the frame 
pivot on road. Have a look at earth moving equipment you will see this 
setup in action.

James Stevenson (TonkaTuf)

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Date: Wed, 27 May 1998 11:35:09 -0400
From: Ed.Wong@astramerck.com
Subject: De Dion Axles

Dean Hufstedler asked what one was...

Well - a de dion axle tries to take advantage of the reduced unsprung
weight of the independent axles as well as the camber advantages of
the solid axles (the wheels are always parallel to each other - unless
the axles tube is "bent").

So remove the diff from the axle and mount it to the frame. Run
"CV" axles between the wheel hubs and the diff. Accomdate for
the change in axle lenghts as the suspension cycles up/down.

It acts like a solid axle, but the diff is not suspended (as normally
bolted in the solid axle tube) by the springs, but attached to the frame.

Its a particularly complex system that takes up alot of room
underneath the frame.

It was originaly done for heavy trucks to keep them from breaking
axles (they were not full floater axles). Its an "old" design - from the
turn of the century actually (when France was the center of automotive
development - as in Panhard et Laveler - and yes the Panhard rod
was invented then too)

EWong

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Date: Wed, 27 May 1998 23:15:58 EST
From: "james stevenson" 
Subject: De Dion Axle

>Could you elaborate on this?  Sounds pretty interesting.

The setup is a 4link type with the upper arms in a V ( the point at the 
axle). Imagine the 4link in the 4runner with the upper arms connected in 
the middle of the axle. This design eliminated the need for a panhard or 
watts link to control lateral movement. The upper link is also called 
an inverted V. This is the setup on the back of the Land Rover 
Discovery and 110. Have a look on my web page you will find a pic of all 
the major link setups including this one 
http://ourworld.compuserve.com/homepages/TonkaTuf/

James Stevenson (TonkaTuf)

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Date: Thu, 28 May 1998 14:52:57 EST
From: "james stevenson" 
Subject: IRS was: Leaf spring alt.

>But again this has not been proven, and I don't believe it will be, one
> way or the other, in the near future. Unless...I think the only person
> who could enlighten this subject with authority would be James
> Stevenson. Have you taken your rig rock crawling lately? 

Don't know if it was a fair test but I was testing TonkaTuf3 all last 
week. I say fair as TT3 had no body on it at the time and I strapped on 
sand bags to simulate the weight of the body and gear in the back. I 
went through some extreme trails, jumped the hell out of it, ran rivers 
and bog holes. I found out a few interesting things First don't run bog 
holes with out the body on or at least a wear and old pair of coveralls. 
Second running rivers without the body on you are going to get really 
wet. Those discoveries aside,  I was testing without the body for two 
reasons 1 the body has not arrived form Japan yet and 2 it much easier 
to film/view the suspension operating without it and to make 
adjustments. As far as on road goes (pirate runs up the highway at 3am 
when the cops change shift) it feels like a solid on 33's considering 
its on 44's and a lot higher, that's not bad. Jumping is much softer on 
the chassis when you land (did some really big jumps on Stockton Dunes 
North of Sydney got it at leat 20 feet up most of the time), Rivers and 
bog holes are much easer. That probably not fair because the whole under 
belly is smooth like a boat hull so it slips through without and real 
drag but its still better. As for Rock crawling this again is subjective 
but it did all of the trails TT2 did no problems no bashing ect. However 
we are talking about a pair of trucks both well over 1000. To put it 
another way TT3 has more travel and articulation than TT2 but I would 
prefer TT2 in the rocks at this point. TT3 is running 44's and TT2 has 
35's but both have simular clearances in the rocks. Overall I Prefer 
TT2, I only prefer the solid TT2 as the IFS/IRS TT3 has a very different 
feel to it in the rocks and is a little unsettling in that I don't know 
exactly how to drive it for best results yet. From the standpoint of 
clearance when fully articulated both TT2 and TT3 are about equal and 
seem to perform about the same over rocks. Its probably a little early 
because TT3 is still an early prototype and I have to do a lot of fine 
tunning. But one thing is obvious in the rocks the ride is much softer. 
That turns out mean, more reliant on the lockers. If the rear drivers 
wheel is lifting on the solid TT2 the front passenger wheel gets a lot 
more contact pressure, but on TT3 the transfer is far less. I am 
currently looking at changing the 2 coil overs on each wheel to remote 
oil supply and making variable valving like the RS9000. I'm going to try 
really hard shocks for rock crawling IFS/IRS so I get some weight 
transfer or in other words try to defeat the independent nature of the 
rig somewhat in the rocks in an effort to induce more traction. I spose 
I could say that the IFS/IRS in TT3 will be far better than most what 
ever way you judge it (when completed) but not as good in the rocks if 
Solid is fitted. As weapon of choice I'd probably prefer 2 vehicles, a 
solid for crawling and the IFS/IRS for everything else. But not to say 
the IFS/IRS is not capable in rocks has heaps of travel and articulation 
more than most modified solids. I suppose someone needs to come up with 
a different test other that RTI as I can fool the test to score way 
higher by pulling up the opposite rear wheel (squatting the ass).  This 
is within the rules of the RTI test but clearly is no benefit on the 
trail although boosting the score

James  Stevenson (TonkaTuf)
______________________________________________________
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Date: Thu, 28 May 1998 07:48:55 -0600 (MDT)
From: Scott Ellinger 
Subject: Re: IRS was: Leaf spring alt.

> That turns out mean, more reliant on the lockers. If the rear drivers 
> wheel is lifting on the solid TT2 the front passenger wheel gets a lot 
> more contact pressure, but on TT3 the transfer is far less. I am 
> currently looking at changing the 2 coil overs on each wheel to remote 
> oil supply and making variable valving like the RS9000. I'm going to try 
> really hard shocks for rock crawling IFS/IRS so I get some weight 
> transfer or in other words try to defeat the independent nature of the 
> rig somewhat in the rocks in an effort to induce more traction. I spose 

Have you considered a form of interlinking of the shocks, or maybe some
other form of linking the suspension to force weight transfer when you
want?

My thoughts were somthing like a single reservoir remote shock with two
shocks on it; I haven't really thought much about it because I feel that 
for my use, it's unnecessary, but it could be useful to you.  To go one
further, one reservoir with four shocks on it, or the like.  Perhaps a
form of air shocks, with a single central reservoir, such that when one
wheel compresses, it increases the pressure to the other three (or which
ever wheels are hooked up to the sustem) so as to provide more of a 
solid axle "feel" to it.

Or, you can just get used to the wierd feeling of independent suspension
in the rocks, in exchange for its ability to outhandle a straight axle
in bumps, jumps, highway, sand, snow, mud, etc.

It's definitely an odd feeling to drive an independent, though.

Actually, truthfully, since my truck is independent, and my first one,
when I hop in a straight axle (Jeep, Toy, or whatever else) it feels
odd and somewhat out of control to me, while independents feel much more
"normal".  :)

- --scott
Scott Ellinger   ellinger@holly.colostate.edu   Larimer County 4WD Club
        Visit my Home Page: http://holly.colostate.edu/~ellinger
 '86 Toy pickup body, Ford 5.0, GMC NV4500, "slightly altered" RKSTMPR

============================================================================
Toyota 4x4 page: http://www.off-road.com/4x4web/toyota

------------------------------

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Date: Fri, 29 May 1998 15:32:36 EST
From: "james stevenson" 
Subject: Re: IRS was: Leaf spring alt.

>In a previous posting describing TT3, you seemed to limit the IS 
>travel to +- 30 degrees. Was there a specific reason for that? Also,
> what CV joints are you using for the inner CV joints?

I was referring to the better CV's like the Spicier 1310 most CV's bind 
at 20-25 degrees where the 1310 gets out to 30. Also I was talking about 
IFS/IRS in general not TT3. On TT3 I use the Spicier 1310 but employ a 
few tricks to get more articulation and longer shafts (to improve 
angles). For example the hand brake is mounted to the front and back 
drive shafts to minimise the width of the disks on each wheel (allowing 
a longer arm). The wheels have a larger offset than normal. Also I use 
Hummer hubs which has an offset (up) driveshaft and gear reduction but 
in. This improves the angles and allows the centre to be higher. The 
Hummer hubs are also narrower as they do not have any brakes. The disk 
are mounted between the CV's closest to the pivot on the chassis. While 
this has heaps of travel / articulation, the limits are the length of 
the arms and the shaft angles. However more would be gained by changing 
to Solid axles. The limits on solids are not the drive shaft angles as 
the length of the shaft is generally 3-4 times longer. With the length 
of the shaft most rigs get away with u joints (15 degrees). When talking 
solids the limits are really in the axle mounting system and the centre 
of gravity. To get the full possible articulation you are talking about 
locating the axle centre at 30 inch below the Tcase output and setting 
up the links for a 53 degree twist. While all of that can be done that's 
an effective lift of around 25inch clearly beyond the centre of gravity. 
That's where the limitation of solids come in. I made the decision that 
the travel/articulation was enough for rock crawling in that it has far 
more than most modified solid you will see on the trail. I did have a 
solid design early on that had the axle below the truss with the pumpkin 
on an airbag to allow travel and a pair of coilovers at 45 degrees from 
the axle to the truss to control sway and articulation. Then a Vlink to 
keep the hole thing straight. Kinda like two triangles pointing opposite 
directions. Its something I might go back to as a dedicated rock crawler 
rig.

James Stevenson (TonkaTuf)


______________________________________________________
Get Your Private, Free Email at http://www.hotmail.com

============================================================================
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Date: Thu, 28 May 1998 22:36:54 -0700 (PDT)
From: Jon Brandt 
Subject: Re: IRS was: Leaf spring alt.

One last thing:
If the diff is located forward from the wheels, so that the axles are 
"swept-back", longer axles can be used. This also limits the total amount 
of movement in the cv's for a given amount of wheel movement. Granted, 
they will never be straight (0 angle), but they will not experience as 
much movement. This is not some wacky idea. I noticed this to be designed 
into the rear suspension of my '69 VW Bug. When they use this same 
platform for Baja racing, they use longer and wider arms. This allows 
dramatically longer axles to be used. By installing this type of altered 
swing arm, these vehicles get over 2 feet of rear travel. I've seen it. 
This is why I was so interested in using this set-up. ...makes me 
[almost] wish I was still in engineering school.

Like everyone has said, its expensive. The parts are easily available, 
though. You can buy the arms, the cv's are the famous Porshe 930 units, 
and custom axles are not outragous. The only problem would be welding up 
a narrow toy 9" unit and constructing a supframe. The problem is not that 
it wouldn't work. Its prohibitably expensive. 

Thanks for the very detailed response!
Jon Brandt

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Date: Fri, 29 May 1998 10:04:41 -0600 (MDT)
From: Scott Ellinger 
Subject: Re: IRS was: Leaf spring alt.

> 	In a previous posting describing TT3, you seemed to limit
>     the IS travel to +- 30 degrees. Was there a specific reason
>     for that? Also, what CV joints are you using for the inner
>     CV joints?
> 
Travel in excess of +/- 30 degrees is extemely difficult to build;
most CV joints are limited to about 30 degrees, at least for full
speed operation.  Also, when you exceed 30 degrees, CV's tend to
lose a great deal of strength; the innards work really hard to get
out, more than they work to turn the wheels.

Additionally, a ball joint with a cycle of greater than 60 degrees
is virtually nonexistant; I just special-ordered what will be my
new upper ball joints; they're 3/4" industrial spherical bearings,
capable of misalignment to 27.5 degrees, and that's the highest I
could find in a reasonable size.  There are some 3/16" sphericals
rated to 35-37 degrees, but they're nowhere near strong enough 
for a vehicle.

There are ways around that 30-degree limit on the joints, but you
have to create something truly unique (and extremely precise, and
very expensive) to do it.  I have one mental design for a ball
joint alternative, but it requires a fully custom assembly, and
I'm not comfortable with the loading that it would have to take,
vs. what the potential impacts on it could be, and how strong it
can be made.

But even if you find ways to play past the 30 degrees on the ball
joints and CV's, in order to maintain integrity on the CV's past
30 degrees, you'd need CV's pushing into the realm of 8" OD, to
make them big enough and strong enough to survive that kind of 
lateral loading and still transmit torque smoothly.  

I'm told that there's a Datsun U-joint IRS setup out there that 
will take greater angles and more torque than a CV setup, maybe
even more than a Porsche 930 joint, but it's a very specialized
joint, and not at all cheap.

- --scott
Scott Ellinger   ellinger@holly.colostate.edu   Larimer County 4WD Club
        Visit my Home Page: http://holly.colostate.edu/~ellinger
 '86 Toy pickup body, Ford 5.0, GMC NV4500, "slightly altered" RKSTMPR

============================================================================
Toyota 4x4 page: http://www.off-road.com/4x4web/toyota

------------------------------

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Date: Sun, 31 May 1998 14:46:41 EST
From: "james stevenson" 
Subject: Why articulation?

>Why do you want articulation for rock crawling instead of simple
> travel to allow the tires to lift over rocks as you meet them?

Because rocks and crevices don't usually hit both wheels at the same 
time. Another reason is relative to Speed. In high Speed Desert running 
your getting air and need lots of travel. If you had lots of travel as 
opposed to articulation on highly uneven surfaces you would have the 
wheels off the ground and that doesn't provide much traction.

James Stevenson (TonkaTuf)

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Date: Sun, 31 May 1998 14:44:02 EST
From: "james stevenson" 
Subject: Re: IRS was: Leaf spring alt.

Jon Brandt Wrote
>If the diff is located forward from the wheels, so that the axles are
>"swept-back", longer axles can be used. This also limits the total
>amount of movement in the CV's for a given amount of wheel 
>movement. Granted, they will never be straight (0 angle), but they will
>not experience as much movement. This is not some wacky idea. I
>noticed this to be designed into the rear suspension of my '69 VW
>Bug. When they use this same platform for Baja racing, they use
>longer and wider arms. This allows dramatically longer axles to be
>used. 

The problem still remains the same the angles. By offsetting the shafts 
you increase the angles reducing the max travel. It was more a function 
of weight than suspension design in the bug. Imagine a rear wheel drive 
with 70% of the weight behind the rear axle. Makes for good wheelies!!!! 
In the racing unit longer arms means you can go wider for the same CV 
angles and also get the benefit of shifting the weight forward.

Bruce Burden Wrote
>I have heard that the Porsche 930 units can go higher, but it will
>require a different boot. So, why the Spicier 1310's? 

The spicier is heaps cheaper and has a more constant supply. They also 
are much stronger. When your going to put 700+ N.M. of torque out the 
engine the gear it down the Porsche units are not going to handle the 
punishment.

>Scott Ellinger and I have kicked this one around. (hand brake
>mounted to drive shafts) I will stick with a rotor at the wheel, thanks.
>No worries about stopping if a half-shaft breaks, and it will be easier
>to work on. But, I guess the Hummer hubs don't offer you a choice.

No the hubs don't. Also You would have to break all the shafts 
(lockers). I do have them on front and back. That's overkill in my book, 
only needed on the back but a requirement to have the E brake on 2 
wheels for rego. The regs are not written that way they say 2 brakes 
unit. Silly stuff

>One other thing - it sounds like you are going to use a fairly stock 
>Toy body. How much of the compression will you be able to use with
>those 44's on it? 

I'm going to use a 4th gen body. Still waiting for the first shipment 
(body plus all interior including trim seats ect.) As for the 44's 
clearing they will go all the way up. The lower suspension arms are 
almost parallel to the ground (equal up/down ,depending on ride 
setting). But forward of the firewall is a custom clip as is the bed. 
However I'm making it the 3rd gen wheel arch style. I hate the 4th gen, 
just me sorry to those that like the look I don't. The clips haven't 
moulded yet but will be 14 inch wider than stock with the 3rd gen type 
flare mouldings on them. The arch is also wider and closer to the top of 
the guard. This also allows clearance of the wheels and most import 
longer  suspension arms without massive flares. Also will have really 
cool moulded running boards down the body inline with the widened guards 
down to the bed. BTW the running boards sit on the frame so they are 
protected. Sounds kinda weird but looks very cool kina looks like a 
monster Vcross with a bed if that makes sense. All up the track is 
widened by 28 inch but distance between the inner tyre walls is 17 inch 
wider. The wheels also have a 5.5 inch extra offset. Was going to give 
that more but wanted the CTIF system clear of rocks. All of that let me 
squeeze in 32inch long suspension arms up from 18 inch on the stock 
track. That gives a 15 inch movement on the arm or 30 inch travel. 

>Or, perhaps a better question is how low (effective lifting the vehicle)
>did you have to mount the diffs to be able to use the compression
>your IS system is capable of?

The centre sits in a truss that runs the length of the frame (its 
actually the frame). The Truss is square and the engine sump sits about 
4 inch off the top of the truss. The Top of the Chev 6.5 will be about 6 
inch lower in the engine bay than normal. The allows the wheel to go 
higher than the top of the engine. Remember the hummer hubs offset the 
wheels down. Its probably equivalent to a 10 inch body lift and a 3-5 
inch suspension but that's kind unfair as the Toyota part is the body 
shell and it designed to run on 44's

Scott Ellinger Wrote
>Travel in excess of +/- 30 degrees is extremely difficult to build; most
>CV joints are limited to about 30 degrees,

Agreed, that's why you are limited to the 30 degrees (less on steered 
axles). Even the joints with 15 or 30 you must look at the rating at the 
max angle. As the strength tapers off dramatically as the angle 
increases from 0

>There are ways around that 30-degree limit on the joints, but you
>have to create something truly unique (and extremely precise, and
>very expensive) to do it.

Agreed that's why I concentrated on a longer arm. But also use 3 cv's 
per wheel to allow the full 30 degree movement.

>having made an IFS Ford 9" myself, it's not that expensive.  It is
>pricey; 

That's well and good but without removing the axle off set in the frame 
you are only really beefing up the centre and or removing any 
limitations in the stock setup. To really get things happening you 
eventually have to centre the axle to increase the length of the 
suspension arms. Two ways to go here a shaft on a permanent angle to the 
axle, not my preference. Or a custom Tcase back casing that has a 
centred output shaft. That's the direction I went for TT3. The other 
trick is 3 CV's per shaft, 2 handle the travel and the 3rd is dedicated 
to the steering. However the shaft to the knuckle needs to be supported 
on a bearing. This allows me to max out the angles to 30 degrees and 
still allow for steering. 

>Interchangeability is a good thing; for that reason, if (when?) I do
>ultimately build a full IS truck (I'm thinking pro tuff truck) it'll 
>run the same spindles, halfshafts, diffs, brakes, etc. all the way  
>around. 

Everything in the TT3 suspension is identical on each wheel and allows a 
swap side to side and front to back. Also keep the tooling costs way 
down. I even do the stage of minimising the number of different bolt 
sizes I use. All goes to bush repairs. The more that's the same the 
easier it is to get going after a failure on the trail. The more that 
common the less spares you have to carry around. I would always rather 
scavenge something from something non essential to get going rather than 
carry more spares.

>As long as you can keep the angles at or below 30 degrees, 930's 
>should hold up fine to just about any smallblock or less, and provide
>lots of travel.

That's fine but drop in a 6.5 Diesel NV4500 ,Marlin gears and push the 
angles out to 30 degrees you have a problem. Also the 930's aren't 
available at the local parts shop in the boonies where you can get the 
spicier parts. 

James Stevenson (TonkaTuf)

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Date: Thu, 04 Jun 1998 01:26:17 EST
From: "james stevenson" 
Subject: Thoughts on Alcans

>How long should the drag link be? 

It's no so much the length as the angles. The idea on the drop draglinks 
is to correct the angles so that the attachment at the steering arm is 
parallel with the road. This means as the suspension moves the 
possibility of hitting the U bolts is far less. A simple solution is to 
flip the steering arm attachment ball. That raises the ball a couple of 
inches and reduces the angles to near stock. Ultimately with big travel 
you have to do this to stop hitting the U bolts and the spring. As far 
as the length goes, whatever distance is between the ball joints with 
the wheels straight ahead and the arm centred.

James Stevenson (TonkaTuf)



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