[Marko_SJ]

This has been a super interesting read.

Cheers.

[DiscoS]

This is all starting to drive me insane, NOTHING, is this complicated.
(All of my terminology comes from SJ80 FSM, no flex)


Wheels need to stay on ground.

Ground isn't flat?

Suspension = coils.

Coils never stop moving?

Damping = Shock Absorbers.

Axle moving uncontrollably?

Locating = leading arms

Axle moving unpredictably whilst cornering?

Transverse Locating = Lateral Rod

Excessive sway?

Extra Roll Stiffness = Stabiliser Bar

Run out of bump?

Bump Stop.

Really uneven terrain tearing leading arm mounts?

Rubber Bushes

In summation:

Coils
Shock Absorbers
Leading Arms
Lateral Rod
Stabiliser Bar
Bump Stops
Rubber Bushes

Is there anything else on the front axle having any impact on suspension functionality?


Assuming no, we simply add up all of the unintended consquences from these parts to figure out what we're dealing with:
Shock Absorbers, nothing
Coils, roll stiffness (due to mounts)
Leading Arms, introduce significant roll stiffness
Rubber Bushes, reduce roll stiffness
Stabiliser Bar, adds roll stiffness
Bump Stops, nothing
Lateral Rod, nothing

So we can see there's quite a lot of roll stiffening components here.
For a car this is all good, but for off-road, this obviously hinders our potential.


Steve, It seems like your job involves suspension, which is an awesome boon for our community and I sincerely thank you for all of your guidance and help you're giving. I would like to ask you, as someone who seems to know his way around the SJ80, about specific problems and limitations facing only the SJ80. Things a general suspension guy may not even consider. I definitely feel like you're too harsh on the APIO kit based off of a single picture and 0 information. Why the hell wouldn't I want adjustable damping in my front AND rear shocks?! You yourself already said the SJ80's problem isn't travel, but roll stiffness! So this kit deals with sway bar, bump stops , caster correction, spacers for sway bar, brake line length, yet it STILL isn't good enough? I feel like you can't see the forest for the trees here, sure your 1" suggestions are ok, but converting the front to a jimny setup is not what I'm looking for, and good luck getting it engineered, let alone insured. If I'm going to go full custom then once again, far beyond the scope of this conversation.

This kit may be pricey at 2400AUD, but how else do I get almost 3" of lift and tackle literally every single area of possible concern that you yourself has mentioned?
It may be pricey, but as far as I can see it's KYB or APIO making half-decent shocks. And considering they're big sponsors in the japanese jimny racing league, I trust all these parts significantly more than any other choice anyone has mentioned, or even found.

[watermouse]

massive bending forces primarily and twist to a lesser extent, although most of twisting of the arm is taken up by the deformation of the chassis end rubber bush. Not to mention compression forces when hitting an object or pothole.

Steve has already explained how radius arms work in an entire thread http://www.auszookers.com/forum/viewtopic.php?f=5&t=47351

(that thread was a lightbulb moment for me.)

[MrRocky]

DiscoS wrote:

My goal, as stated in my build thread, is to respect the original intent of the car, but acting like the Sierra cost double what they charged. I want minimal custom work, this car isn't about flex, lift, power, traction, or even style. It's about building a pure fun off-road weapon. Think an 86 with 4wd.

Sounds like you need a body lift, tyres, guard trim/bash and a locker. Is there really much point in going into it so much. Fix/strengthen stuff as you need and wheel the hell out of it.
As far as suzukis go im yet to see a kit that offers really good offroad performance, mix and match, trial and error is the best way when taking the road less travelled

[got_bar_work]

Its a 80in wb u dont need any lift. Cut the guards and run bigger tires at lower pressure will give u a better ride then any lifted spring combo will. When i put the king ultma kit in mine years ago it lifted it 60mm. Gears and tires are the most important things on a 4x4. Get them sorted first then see what u need

[DiscoS]

Thanks for that guys, I really appreciate everybody pitching in, and they're all great ideas for what I want from MY rig, but I'm trying to talk everything out publicly so later on, someone else can read this and learn. I've got my own build thread where I'd love to hear your advice, you can check my current build, with all its huuuge pictures, why az doesn't resize them is beyond me..

So try and keep everything here as general as possible, things holding back flex for ALL sj80s, like removing sway bar. That is news to me and exactly the kind of stuff I'm looking for!

[Gwagensteve]

I'm on my phone at the moment so I won't answer in detail, but if you've read my posts on this topic and it hasn't dissuaded you from buying the APIO kit, I don't know how I can help any more.

Your $2400 is going to get you a tall car with no increase in travel and flex and no improvement on the actual problems of the SJ80 suspension, all of which are exacerbated with lift.

Steve.

[got_bar_work]

Its easier to add a rear sway bar to increase rear roll stiffness to force the front to work then it would be to try and lower front roll stiffness with out completely redesigning the entire front end. If u camp out of the car u will want to get some stiffer rear springs like kings or u will be forever draging its ass

[Gwagensteve]

DiscoS wrote:

Why the hell wouldn't I want adjustable damping in my front AND rear shocks?!

Because you don't have adjustable spring rate. Trust me, as someone who spent lots of money on adjustable shocks - it's a pointless gimmick. Properly valved shocks for the spring rate and vehicle is all that's required.

Quote:

So this kit deals with sway bar, bump stops , caster correction, spacers for sway bar, brake line length, yet it STILL isn't good enough? I feel like you can't see the forest for the trees here.

It's not good enough because it's pointless money spent. All those parts are only required because the car is being lifted excessively and they are workarounds to try and make it drive properly. They aren't there for any other reason.

Quote:

sure your 1" suggestions are ok, but converting the front to a jimny setup is not what I'm looking for, and good luck getting it engineered, let alone insured. If I'm going to go full custom then once again, far beyond the scope of this conversation

There is no problem engineering or insuring a swap to jimny coil hats and shock mounts.

Quote:

This kit may be pricey at 2400AUD, but how else do I get almost 3" of lift and tackle literally every single area of possible concern that you yourself has mentioned?

It tackles NONE of the areas of possible concern. It only introduces a bunch of new ones whilst exacerbating all of the existing problems with the SJ80 suspension.

Quote:

It may be pricey, but as far as I can see it's KYB or APIO making half-decent shocks. And considering they're big sponsors in the japanese jimny racing league, I trust all these parts significantly more than any other choice anyone has mentioned, or even found.

KYB do indeed make quality shocks, but never, ever confuse sponsorship with implied quality. Don't confuse money spent on parts with necessity either.

I'm not concerned with whose sticker is on a part, what colour it is, or how much it's worth. I'm only interested in proven performance. That APIO kit, in order to lift the car 3", will have stiff springs, stiff shocks to control the stiff springs, and high front roll stiffness. That's because it's not possible for anyone to achieve 3" of lift any other way when using the stock spring and shock mounts. So, you can have (A) a tall car, or (B) a car that works properly, or (C) a car that's custom fabricated. You can have A or B, but you can only have A AND B with C.

I spent lots of time working on an SJ80 many years ago which was built with custom springs and custom built Koni shocks all round (including the front struts) It cost ALL THE MONEY. It didn't have caster correction bushes, so we rolled the front diff back to increase caster without using stiff bushes. It DID have urethane bushes in the rear to increase rear roll stiffness. (which lead to broken rear radius arm brackets.

It still had excessive front roll stiffness, wouldn't flex when climbing, and wasn't measurably better than leaf sierra in any way.

Steve.

[DiscoS]

Ok, so tactic change, the stock setup is FUBAR, let's fit Jimny seats.
(I'm aware this is now retreading common ground, but I'd really like to keep fleshing this thread out so, so we have an SJ80 bible of suspension, for now and forever, as a constant resource and reference for everyone)

So with installation:
Are we replicating the SJ80 original seating positions?
Moving axles seats inboard?
Moving chassis seats?

If we're keeping the seats in roughly equivalent positions, won't we just have an easier time sourcing parts for a still less than optimal suspension geometry?
How does the Jimny setup deal with our original problems with excessive roll Stiffness, limited travel, etc.?
I guess it's going over my head right now (definitely need some dindins), but what does swapping to the jimny setup actually achieve?


Beyond everything we're discussing, a big question nagging in my brain is, if we boost roll stiffness in the rear to make the front work a bit more, aren't we running the risk of constantly breaking and destroying our trailing arms and their axle/chassis mounts?
All the custom work with seats, shocks, coils, means nothing if all that does is constantly push the arms and their mounts to do work that they're just not capable of doing (and sustaining). I was hoping by designing a new trailing arm, that it would lower the necessary force to flex the axles down into a region that would also greatly reduce the risk of having the arm mounts fail catastrophically. Unless I'm missing something the greatest flaw of the SJ80 setup is the design of the arms! (and has already been said, radius arms can offer huge travel, but they also severely limit flex!)

[Gwagensteve]

To fit Jimny coil and shock mounts:

Remove the Jimny coil and shock mounts from a Jimny chassis.

Remove the jimny coil seats from a jimny diff

Remove the same from the coil sierra.

Weld Jimny parts to coil sierra.

Yes, the suspension will still be sub optimal. It will continue to be sub optimal all the time it's based on radius arms, but you've ruled out converting the front end to three link so that's the parameters you're working with. Using Jimny parts opens up a huge range of coils and shocks you can use to achieve the ride and travel you want. You don't have that choice now.

If you're welding new coil seats onto the axles it's a no brainer to roll in more caster and doubling plate the radius arm mounts to prevent breakage.

The Jimny still suffers from excessive front roll stiffness. It has its own problems. But it has less problems than a coil sierra.

No, adding roll stiffness to the rear via a sway bar adds absolutely no stress on the axle brackets. None.

The greatest flaw of the SJ80 suspension is the front strut. The second greatest flaw is the front radius arms. I'm suggesting you remove the greatest flaw. Removing the second greatest flaw requires the elimination of the radius arms. That involves complex fabrication and will be very challenging to engineer. (no factory vehicles run a three link front, so there is no precedent.) designing some sort of whacky flexible radius arm will freak out an engineer and cause all sorts of potential problems.

The custom SJ80 radius arms (such as the white Japanese ones) you've posted don't actually remove roll stiffness. Mostly they allow adjustment of caster without using caster bushes.

Steve.

[got_bar_work]

Jimny have the same problems. Yesterday i watched a stock jimny with a rear locker trying to climb a ledge. It had the sway bar on and was driving up hill. The weight transfers back flexes the rear and the front was just lifting a wheel off the ground. It did not flex at all. Zero. So from that we can see that the sway bar has to go . And the rear needs a swaybar. U want to get fancy in the front i would keep it stock and put cross linked airbags under the chassis. It will give u a small lift but it also might force the front to flex more

[DiscoS]

Cross linked air bags?
That's only an option for the jimny setup right?
(Sj80 already has things in its coils)

So 3 link versus custom radius arms, it would be best to talk to a VASS engineer to see what they're more comfortable with?
What are thoughts on like, a jeep jk setup? (5 link I believe)
I know a lot more about linkages now, and everything I linked to on front page was simply to try and visualize what I was talking about. I don't think the design I'm envisioning exists on the market right now.

Ok, is the "front strut" the sway bar?
Something I'd like to touch on is road handling. From here on, anything above 60 km/h is what I mean by high speed conditions. I don't know about other's here, but I drive my baby, very, very hard on the road. Since going to 30's, I've noticed everything involving handling is worse. That's not a surprise, but it's been mentioned the car was designed to understeer, and the sway bar is a part of that, but my car CONSTANTLY wants to step out, and I don't know if I could handle less understeer.

On a similar vein, I'd like to touch on tire pressure. Whist not necessarily specific to this car tire pressure has a major impact on the way the car handles and its performance dynamics. As of right now I believe that what is important when changing sizes of tire is maintaining the same quantity of air within the tire. This would mean as a tire holds more volume pressure needs to decrease and vice versa. Based on my math, 20 psi on 205/75r16 means 16psi on a 225/75r16. Does that sound right?
I made a spread sheet to do the maths, I'm happy to upload it if can do that somehow.

[got_bar_work]

U could make some kind of sway bar disconnectes
I ment put black Airbags under chassis where the bump stops are if there is room. Not the crappy red or blue ones that go in the coils

[Gwagensteve]

DiscoS wrote:

Cross linked air bags?
That's only an option for the jimny setup right?
(Sj80 already has things in its coils)

I do not believe that cross linked air bags will really help. They won't reduce the roll stiffness inherent in the radius arms. They will only add spring rate which will increase unloading when climbing. (the tendency for the suspension to open up)

Quote:

So 3 link versus custom radius arms, it would be best to talk to a VASS engineer to see what they're more comfortable with?
What are thoughts on like, a jeep jk setup? (5 link I believe)
I know a lot more about linkages now, and everything I linked to on front page was simply to try and visualize what I was talking about. I don't think the design I'm envisioning exists on the market right now.

Yes, involving a VASS engineer early is the only way to ensure you get the car approved for road use.

I don't like 5 link front setups - they work their bushes very hard and are difficult to package, but you may have difficulty engineering a three link due to the forces the upper link experiences under braking.

Tell us more about your design. I can almost promise you it's been used or tried.

Quote:

Ok, is the "front strut" the sway bar?

I have no idea what you mean by this. SJ80's don't run a "strut" (as in McPherson Strut) - they run a sort-of coilover. Neither serves the function of a sway bar.

Quote:

I don't know about other's here, but I drive my baby, very, very hard on the road. Since going to 30's, I've noticed everything involving handling is worse. That's not a surprise, but it's been mentioned the car was designed to understeer, and the sway bar is a part of that, but my car CONSTANTLY wants to step out, and I don't know if I could handle less understeer.

The problem you're describing sounds like a driving style issue. I get the impression you have come from a performance road car background? 4WD's require a very different driving style where you're always managing weight transfer and all your inputs need to be timed to the speed the car weight transfers. It's quite easy to provoke a slide in any 4WD in H2, but the car has to be "tipped in" by reasonably quickly forcing a direction change. In a steady state cornering situation the car should understeer.

On a similar vein, I'd like to touch on tire pressure. Whist not necessarily specific to this car tire pressure has a major impact on the way the car handles and its performance dynamics. As of right now I believe that what is important when changing sizes of tire is maintaining the same quantity of air within the tire. This would mean as a tire holds more volume pressure needs to decrease and vice versa. Based on my math, 20 psi on 205/75r16 means 16psi on a 225/75r16. Does that sound right?
I made a spread sheet to do the maths, I'm happy to upload it if can do that somehow.[/quote]

I'm a little confused by this. How are you using a spreadsheet to determine ideal tyre pressure? Whilst I don't advocate running higher pressure than placarded, and I broadly agree that pressure in a stiffer LT tyre can be a little lower than the placard recommends, 16 psi sounds too low if indeed you do drive it hard on road. I'd go back up to 20 and see what it does to your handling. You may find the reduced contact patch and increased lateral stability increases understeer.

[fordem]

DiscoS wrote:

On a similar vein, I'd like to touch on tire pressure. Whist not necessarily specific to this car tire pressure has a major impact on the way the car handles and its performance dynamics. As of right now I believe that what is important when changing sizes of tire is maintaining the same quantity of air within the tire. This would mean as a tire holds more volume pressure needs to decrease and vice versa. Based on my math, 20 psi on 205/75r16 means 16psi on a 225/75r16. Does that sound right?
I made a spread sheet to do the maths, I'm happy to upload it if can do that somehow.

I'm curious as to how you arrived at this conclusion.

When dealing with air, or any other gas, pressure & volume are linked - let me explain...

For ease of understanding, let's use a 20 litre fuel container, to which we have fitted a schrader valve - when there is no fuel in the container, it will contain 20 litres of air at atmospheric pressure, or 1 atm (roughly 15 psi), using a compressor we can pump another 20 litres of air into the container, the pressure will now be 2 atm (30 psi), add another 20 litres and we have 3 atm (45 psi), and so on - the limit to how much air we can put in the container is dependent entirely on the strength of the container - a fuel container (or a tire) will rupture at relatively low pressures, but a properly designed pressure vessel (for example, a scuba tank), can hold many times it's actual volume in compressed air (in excess of 200 atm).

The flip side of this is if you pump the same volume of air into a larger container, the increase in pressure is less - a 40 litre container, with no fuel, will contain 40 litres of air, at atmospheric pressure, add 20 more litres and it will be at 1.5 atm, so a larger container, with the same volume of air added, will already be at a lower pressure.

Tires, because they are not "rigid" vessels, make for a much more complex scenario - as you inflate the tire, it expands, so that the calculation is not a simple mathematical one as in the case above.

[Gwagensteve]

Quote:

On a similar vein, I'd like to touch on tire pressure. Whist not necessarily specific to this car tire pressure has a major impact on the way the car handles and its performance dynamics. As of right now I believe that what is important when changing sizes of tire is maintaining the same quantity of air within the tire. This would mean as a tire holds more volume pressure needs to decrease and vice versa. Based on my math, 20 psi on 205/75r16 means 16psi on a 225/75r16. Does that sound right?
I made a spread sheet to do the maths, I'm happy to upload it if can do that somehow.

Woah. I'd missed this volume theory.

If I understand your theory to have the same volume of air in my tyres as stock they'd be at 5.5psi.

I do run 5psi off road, but on road I run 18-20, because my tyres have quite a low load rating and are a flexible carcass.

[alien]

^^ this

It needs to scale based on the construction of the tyre and not just volume alone.

the 4psi method and just checking the actual contact patch (chalk or water) are really the best way. Then adjustments from there based on what you're after (ie: more pressure to corner better or less pressure for a softer ride).

I've had several brands of 31" tyre on my sierra and all of them require different pressures both on and off road to work effectively, even though they're mostly the same load rating. As a rule of thumb though, 26psi in the front and 22psi in the rear tends to work well across the board. When i had Simex Pedes i was down around 22 front and 18 rear to get a good contact patch, but opted to go up in pressure for less sketchy cornering and easier steering.

[coneykid]

Has anyone ever cut the spring mount on the chassie and risen it to fit a bigger or longer strut? If so was it worth it. Or is a coily only built for the beach?

[Gwagensteve]

Firstly, It's not a strut. Its a sort of coil over. A strut is a completely different thing relating only to IFS where it forms the upper suspension link. A Vitara runs a strut with no coil attached. Most modern road cars use a strut with the coil attached.

Not that I'm aware of coney, because if the upper mount was raised much at all:

The geometry change between full droop and full compression would see the shock hit the coil hat

There aren't any off the shelf shocks that contain a coil carrier in the right spot

It's much easier to just separate the coil and shock using the parts from a wrecked jimny, then off the shelf coils and separate shocks can be used.

[MrRocky]

Seems alot of tech and talk for a swb on a 30" tyre
What are you trying to acheive/drive whats the end goal
If you want to add uber flex then your going to struggle and run out of wheelbase when you do.
If your going to uber mod the car and run a 30" tyre the said uber mods kind of become pointless.
I just cant figure out where any of this is going

[watermouse]

MrRocky wrote:

What are you trying to acheive/drive whats the end goal...


...I just cant figure out where any of this is going

DiscoS wrote:

My goal, as stated in my build thread, is to respect the original intent of the car, but acting like the Sierra cost double what they charged. I want minimal custom work, this car isn't about flex, lift, power, traction, or even style. It's about building a pure fun off-road weapon. Think an 86 with 4wd.

[Gwagensteve]

I have no idea what a "weapon" is, but I'm pretty sure it's not any more than a rear locker.

[J--A--C--K]

This has been a good read.
Hats of to all the tech.

[alien]

a toyota 86 with 4wd would be boring... i've not driven one, but by all accounts the reason they are fun is because the RWD and skinny tyres makes them a bit tail happy even though by modern standards they're not all that powerful or sophisticated.

If i was building a sierra today, i'd start with a leafy, do a proper RUF conversion, run 30x9.5's with tcase gears, full float rear w/ discs, crmo front, ARB front and rear lockers and a g16 efi under the bonnet... that would shit all over most other 4wds and be crazy reliable without attracting much attention from the law.

Now, if someone asked me what they should do to their sierra? well, i'd say keep it stock, chuck a locker in the back (air preferably) and drive the pants off it.

[MrRocky]

Full float rear pointless unless u running 33"s or bigger and 30"s cant drive diddly squat

[alien]

Full float was more to get the rear discs plus reliability with a locker in the back.. it's overkill but why not =)

[jdk81]

alien wrote:

Full float was more to get the rear discs plus reliability with a locker in the back.. it's overkill but why not =)

Better wheel bearings too

[coneykid]

I was just looking at my front end in the coily. Has anyone ever lengthen the shock mount and fitted a longer shocky and welded the spring mount into the new shocky and added slightly longer soft spring? (Obviously striping a shock before welding if you can strip them?!)

[epitam]

I did it... search israeli coily on readers rides.

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