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Suzuki SJ413 LWB build

37K views 61 replies 14 participants last post by  Lysy 
#1 · (Edited)
SJ413 LWB link suspensions question

HI guys,

i'm not realy new to this forum, i have been reading here for years.
but now i want some people to look at my suspension design before i start building it.

i have some 3D drawings i would like you guys to give your opinion on.

Picture 1:
side view


Picture 2:
view from top


Picture 3:
view from under


Picture 4:
custom crossmember for gear-box,T-case and 3-link mounts


Picture 5:
Front axle with 3-link


Picture 6:
Rear axle with 4-link


Picture 7:
Rear axle "Bridge" with brackets


Picture 8:
Rear brackets on chassis and extra crossmember


Picture 9:
Other view of custom crossmember


Picture 10:
Front axle flex

Picture 11:
Rear axle flex


I would like some input before i get all the brackets laser cut.

about the build,
* 2,5" airshocks with 16" travel in the front
* 2,0" airshocks with 16" travel in the rear
* 35x12,50 tyre's
* Nissan Patrol axle's (4.11 ratio)
* Front and Rear air-locker
* 5.14 T-Case
* Vitara 1.6 engine or volvo (need more info on the volvo, haven't found a decent build thread)

you can also visit my website to see more about this project
LWB Project Archives - SUZUKI-4WD
 
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#2 ·
The one thing I see first is in the rear. The top arms that mount to the frame should be higher. They way they are now, when the axle drops, it will twist down, pulling on the drive shaft. Not what you want.
I also don't see the front axle flex shot. I'm wondering how you are going to keep is located.
 
#3 ·
very nice model and bracket design


Looks like a lot of rear steer when flexing, so what he said^.. do you have your numbers figured out regarding anti squat etc. ?


volvo swap is the most common swap in trial up here, they are heavy though and Im not a fan. But something like volvo t5 Im a big fan of :grinpimp:



what CAD-program are you using?
 
#4 ·
We used "inventor" from "Autodesk" for the drawings.

the front flex picture didn't made it during upload, i will redo it ASAP.
the front axle is going to held in place with a panhard bar offcourse.

don't realy get what you mean with rear steer, and what do you mean with "the numbers" ?

and where can i get some decent "how to install a volvo engine" info ?
 
#7 ·
On the rear raise your axle side lowers to axle centerline and move your frame side lowers closer together and down some. Lower links look like they have a bit of angle on them, that combined with them being parallel to the frame will cause the axle to "steer" in relation to the frame during articulation. This will throw you off your line off road and induce roll oversteer which will make it a handful on the road.

The rear also looks like it would have a ton of anti squat because there is not much vertical separation between the frame side uppers and lowers. Moving the frame side lowers down would help this.

I could not see if the front axle lowers were below centerline but if they are move them up and drop the frame side upper the same amount in relation to the frame side lower...then drop then drop them both down to flatten your links

Did you factor in getting your exhaust past that front upper link? Why not put it on the right side. It will help keep the pinion pointed at the t-case during articulation and ease exhaust routing.
 
#9 · (Edited)
On the rear raise your axle side lowers to axle centerline and move your frame side lowers closer together and down some. Lower links look like they have a bit of angle on them, that combined with them being parallel to the frame will cause the axle to "steer" in relation to the frame during articulation. This will throw you off your line off road and induce roll oversteer which will make it a handful on the road.

i did the lowers on axle below centerline to get more distance between the links, this should be a good think right ? and what's the down side of placing it off center ?

The rear also looks like it would have a ton of anti squat because there is not much vertical separation between the frame side uppers and lowers. Moving the frame side lowers down would help this.

did place them next to the chassis for clearance, but if it's that much of a problem moving them under the chassis like in the front would make it okay ?

I could not see if the front axle lowers were below centerline but if they are move them up and drop the frame side upper the same amount in relation to the frame side lower...then drop then drop them both down to flatten your links

What you are saying is that the space between upper and lowers should be the same on the chassis as on the axle ?


Did you factor in getting your exhaust past that front upper link? Why not put it on the right side. It will help keep the pinion pointed at the t-case during articulation and ease exhaust routing

i wish i could, but there is no space to weld that on. the diff housing is made from cast-iron so i cannot weld there. the rest of the axle piece on the right side is already crowded, Panhard mount, airshock mount and the link mount

.

picture of front axle
 
#11 ·
#1 you need vertical separation at the axle but you are adding angle to your lower links and sacrificing ground clearance by hanging the lower links below the axle. You would be OK with 7-10" of very separation.

#2 I would put them even closer together than under the frame. About 8-10" apart would work well.

#3 you want a little less vertical seperation at the frame than the axle. There are a lot of variables so I can't give you an exact number for your application but ideal is going to be somewhere between parallel and what you have in the rear.

#4 could you add a mini truss over the center section to mount your upper links to
 
#14 · (Edited)
Kinda what I was thinking. Far off ICs create much more AS/AD change thru suspension travel. Converging links more(side view), while still creating 'ideal' numbers is probably preferred as the closer IC is to the suspension the less it deviates from what it is at ride height. His rear does this, very much, but he also has a very definite positive roll axis(yuck). And thus, the 'rear steer'. Front ends not definined completely, there's no panhard, but the pics look cool:)

But, I was wondering if there's something missing in that? I've seen a few threads where the IC way out somewhere in front or behind was a benefit, but don't recall the theory or mechanism behind that idea?
 
#15 ·
Kinda what I was thinking. Far off ICs create much more AS/AD change thru suspension travel. Converging links more(side view), while still creating 'ideal' numbers is probably preferred as the closer IC is to the suspension the less it deviates from what it is at ride height. His rear does this, very much, but he also has a very definite positive roll axis(yuck). Front ends not definined completely, there's no panhard, but the pics look cool:)

But, I was wondering if there's something missing in that? I've seen a few threads where the IC way out somewhere in front or behind was a benefit, but don't recall the theory or mechanism behind that idea?
To get a little more specific, looking back at some 4 link calcs I have saved my IC's seem to end up around 90-100", again, not because I put them there but because that's where the numbers I care about put them. I agree that it needs to not be way out there in either direction but it works well for me where it has been landing.

I think there is lots of theory that is supported by the math but not rooted in reality. Especially things that happen at the extremes of wheel travel in a low traction environment. I love the math/geometry side of suspension design but the reality is that for what we do there is a pretty wide sweet spot in the numbers.

That being said I think the OP's current design falls well outside that sweet spot. While it is true that his AS won't change much at all through travel it will start out a lot higher than where it would end up on droop with a longer IC... so he is not gaining anything at droop and loosing big time at ride height.

I am totally spitballing here but lets throw some rough numbers around in the OP's case. lets call his current setup 140% AS at ride height and 145% at droop. If he increases his vertical separation at the frame he will lengthen his IC but drop his ride height AS to say 70%, at droop the longer IC causes his AS to jump to 100%. Sure his AS changed more but he is still better off with the longer IC in all conditions. There is a middle ground there but it can start bringing other compromises into play, this represents the extremes to show that they really are not that extreme.
 
#16 ·
Just spend a couple of hours making some changes in the design.
i'll tell what we have done in every pictures and i would want to know which option gets closer to the best setup.

in all option's you can see "ride hight" and "10" drop":)

Option 1:

we changed the following for this option.
1. we raised the axle lowers in the centerline of the axle (front & rear)
2. we raised the rear chassis uppers 4"

Option 2:

we lowered the the rear "lower" chassis mount by 1,5" and 7,4" closer
together

Option 3:

we have done some more here.
1.lowered the upper chassis mounts by 2" (compared to option 1)
2.we made the bottom link longer to 100% if the upper is 70%
(upper hart of joint to hart of joint 35,2" and the lower 39,37")

i would like some input on which design is best, and what can be improved on it ?

thank you for your time, and reactions.
 
#17 ·
You are heading the the right direction. The frame side uppers are a little too high in option 1 and 2 but look better in #3, They might still be a touch high but it is hard to say without running the numbers.

lower link frame mount height looks better in option 2 and 3 but could go even lower for flatter links (bring the uppers down the same amount), You could achieve the same thing by lowering the ride height unless there is some other reason not to.

I like the upper and lower links to be a little closer to each other in length than #3 shows, it will help keep the pinion from rotating down on droop. I often make the the uppers as long or longer than the lowers. I do like the length of the lower links in #3 so maybe lengthen the uppers.
 
#18 ·
I ran some rough numbers for you based off my best guess form looking at your drawings. The two biggest things we are looking at are anti squat (AS) and roll axis angle (RA). I like to set AS at 50-80% and RA a degree or two negative.

Here is where you started out. Way too much AS and a whole bunch of positive RA
Technology Electronic device Screen Electronics Line

Text Font Number




Here is where you would be if you did some of the things you talked about in your last post.
-Move axle lowers up to axle centerline
-Move frame lowers down 1.5"
-Move frame lowers in 4" on each side
-Move frame uppers down 2"

As you can see things are looking a lot better, this would work pretty well but there is still room for improvement

Text Font Number


Here is where you would be if you lowered your ride height 1" or moved you upper AND lower frame side mounts down 1" from the last set of changes. This really puts your suspension geometry in the sweet spot.

Text Font Number
 
#19 ·
first of all, WOW !!!
thank you for running "the numbers" for me, i don't understand this form
since there are alot of parameters i don't have like the "CG" and i also couldn't find this document anyway.
i can provide you some more exact numbers if you tell me what you need.

back to the design.
i could lowered the "ride-hight" by 1" no problem, but i want to keep the body as original as possible. and i can always do this by bleeding some air out of the shocks they will we be set a 6" in and 10" out travel.

i also so could lower the upper and lower mount by 1" that's no problem i think.
what i can't do is make the uppers longer, because of in the original design i set them at 45degree's (what you read everywhere) and you should not go belowe 40 degree's and they are at 40 degree's in my "Option 3".
so if it's desired that the length difference should be less, i could shorten the lower link. i'll have my brother make a screenshot from the bottem, and i'll post it here asap.

thanks for reading and replying on my topic.
 
#21 ·
first off, my last post was a little bit of a mess for a minute, I was bouncing back and forth between my phone and computer and having internet issues so please go back and read the final version because I don't know exactly where it was when you saw it.

By moving the frame side lowers in you are adding triangulation to them, this will allow you to reduce the triangulation on your uppers while still having enough total triangulation to keep the axle in place. 40 deg total triangulation is a safe minimum number but that means if you are getting 20 deg from your lowers you only need 20 deg from your uppers to total 40 deg

If you are planning on using all of that 16" shock you should be running a 38-40" lower link and at least a 32" upper.

I just realized I did not set the link length correctly in my calcs, if you run a 40" lower and a 36" upper you should lower the frame side upper 1" from where I told you in my last post. That means if you go ahead and drop the frame lower link mounts the extra 1" (total 2.5") you do not have to change the upper link height. If you only drop the lower 1.5" you would raise the upper 1"
 
#23 ·
Couple people already touched on it but adding a simple form fitting truss to the front and moving the mount to the passenger side will vastly help your up travel and compression and/or ability to maintain those and keep your ride hight in check.

I'd take a look at your drivetrain hight in relation to where it will be placed in the frame rails and your hood height.

In the right direction no doubt.
 
#24 · (Edited)
thanx for your input !
but we are now busy with the rear, and i think the front doesn't need much work.
i will move the front upper to the frame and lower the "tower" on the axle.
we placed it there so we could fit the exhaust between the link and the frame.
but it looks like it better to place the link net to the frame and then the exhaust.

Dr. AM4x4 is going to run the numbers for me, and i will give him the front numbers as well.
and i hope he will insert them 2. i would love to se what this all does, before we go to the laser cutter company we will post a video on how all of the suspension moves and you guys can shoot at that again and we will keep tweeking the suspension within the limits of the possibility's.

Thanx !

For more about this project or other projects i did go visit:
SUZUKI-4WD
 
#26 ·
You asked me to measure at the frame but you haven't told me where.
So i have all the dimensions taken from the axle centerline
in the middle where it hangs the lowest and measure to the bottom of the frame to the ground. Lets also get a measurement from the center of the axle to the bottom of the frame (in the middle where you are taking the other measurement)
 
#27 · (Edited)
There we go, option 4,

what have we done.
* lower axle links as wide as possible
* lower frame links
* upper link length as long as possible



with video clip: 4 link on Vimeo
-------------------------------------------------------------------------
anyway here are the dimensions: (center to center)
distance between lower link mounts on axle : 43,8"
distance between upper link mounts on axle : 6,5"
distance lower links mounts on frame : 25,47"
distance upper links on frame : 20,15"

height of upper links on the axle center link of axle: 7,72"
-------------------------------------------------------------------------
other dimensions:
length of upper links (center of joint to center of joint)
Upper length: 31,89" (no more room for longer length)
Lower length: 39,35"
-------------------------------------------------------------------------
Next dimensions are measure from the centerline of axle, since i did not know where you want me to measure on the frame, besides you also don't have a clue of the dimensions of the suzuki frame. (we use tha CAD program at my brothers house, and i'm typing this in my own house)

there we go.
Upper frame link. 29,92" away from center of axle.
Upper frame link. 7,79" above centerline of axle.
-------------------------------------------------------------------------
Lower frame link. 42,12" away from centerline
Lower frame link. 3,54" above centerline of axle.
-------------------------------------------------------------------------
Crankshaft 17,71" above centerline of axle.
-------------------------------------------------------------------------
Lowest position above centerline of axle 5,9"
Center of axle above floor 17,5" (half of 35" tyre, tyre not bought yet)
-------------------------------------------------------------------------

i hope these last dimensions mean anything to you.
i think these measurements are better the measure from the frame where you have no clue how big everything is.

Thanx again.
 
#28 ·
At a glance your model looks really good but I still need to run the numbers to confirm. Can you also get me the height of the upper and lower links at the frame. You can get me a measurement from the bottom of the frame or from axle centerline. I had not asked for these numbers before because I was going to tell you where to put them but I want to see where you are in that last drawing. I also forgot to ask for your wheelbase so let me know what that will be.

One other thing to consider is that a 35" tire will not give you a 17.5 axle center height. Most tires are smaller than advertised and you have to account for tire squish when aired down. You will probably be around 15-16" depending on the tire and air pressure
 
#29 ·
At a glance your model looks really good but I still need to run the numbers to confirm. Can you also get me the height of the upper and lower links at the frame. You can get me a measurement from the bottom of the frame or from axle centerline. I had not asked for these numbers before because I was going to tell you where to put them but I want to see where you are in that last drawing. I also forgot to ask for your wheelbase so let me know what that will be.
I hope this image gives you all the info needed.


Note: all dimensions from centre of the axle

One other thing to consider is that a 35" tire will not give you a 17.5 axle center height. Most tires are smaller than advertised and you have to account for tire squish when aired down. You will probably be around 15-16" depending on the tire and air pressure
i know but i haven't made the tyre choice so we have use a dimension that isn't to big. so the tyre will Always fit.

Thanx again for helping me out !!
 
#30 ·
That actually looks really good. Anti squat looks great and you are at 0 deg roll axis which is not bad, but a little negative would be better. You could improve on the roll axis angle by moving the frame lowers closer together, 16-19" apart would be ideal and would put you at negative 1-2 deg. The other advantage of moving them closer together is that you would be less likely to hang up on them.

The only other thing I would suggest is moving the axle uppers a little closer together. It will not change any of the numbers but it will give you a little more triangulation for locating the axle. You should be able to put them about 5" apart.
 

Attachments

#32 · (Edited)
@ am4x4,
we did get the upper links on the rear axle 1" closer together, so that's a little better for the triangle.

anyway, now it's time for the FRONT


we are still busy with the design of the panhard bar, but we already have the dimensions.


i hope every dimension makes sense and is usefull.

and a view from the bottem.


Thanx again for your help am4x4.
(would you like your website link on my website ?)

happy holidays !
 
#33 ·
Finally made time to run those front numbers

Here is where you are now. AS looks real good but your roll axis could be better. I think you also need longer lower links and a little bit less angle on the links would be a big benefit.
Text Font Parallel


To improve your roll axis you either have to raise your panhard or lower your frame side links. You could also improve it by moving your frame side lowers closer together but you already have quite a bit of triangulation on them so I don't think it would be a good idea to add more.

Here it is with 3" longer lower links, lower links moved down 1" at the frame and upper moved down 2" at the frame. As you can see, your roll axis is slightly negative and your links are a lot flatter.
 

Attachments

#34 · (Edited)
Thanx again for the help, buti have to wait on my brother for the adjustments (he does the cad drawings, does that sound familiar :) ) so that will be next year.
I will be looking in what is possible.
I don't want to end up with the front and rear lower links next to each other on the frame.
And i also want the lower links lower on the frame then needed.
Don't want to hang on those points either, since the lower frame links are allready on a custom crossmember i can't move them any further back.

(the crossmember supports the T-case,Gearbox, upper and lower links)
it's possible to lower the upper framemout or do something with the panhard.

Did i mention that this car also needs to be driveable on the street,
That might have some influance on the setup ?
Main goal is technical driving NO mud bogging.
 
#35 ·
It will probably work just fine where you had it, I was just showing you best case scenario. I am designing for street and off road, understeer is especially important on road which is why I keep pushing you towards it.
 
#37 ·
We are now at the point that we redraw all the brackets, we are happy with the numbers.
Next up is to put the airshocks in the drawing and figure out how to position them.
Does anyone know if the airshocks shouls be at a 90degree angle on the axle or should point them inwards,and what are the effects of it ?
 
#38 ·
Time for an update on the design

the design is now where i want it.
Next up is the shockmounts with higth adjust possibilty.
anyway the design screenshots so far:










i want to be able to adjust the ride not only with the amount of air in the shocks so i will make a hardware solution of 5 positions each 30mm apart. this also makes it possible to play with the airshocks in/out ratio. i'll start with the hardware mount in the middel and the shocks set at 6" in travel and 10" out travel.

any comment or input is welcome on this idea (maybe someone did such a hardware solution and you how it's been done and want to share this info)
 
#39 ·
Looks good...what are your plans for the rest of the steering? It looks like the axle side panhard bracket might be in the way of the drag link when the steering it turned.
 
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