Pirate 4x4 banner

1 - 20 of 62 Posts

·
Registered
Joined
·
31 Posts
Discussion Starter #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
 

·
Registered
Joined
·
4 Posts
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.
 

·
Registered
Joined
·
31 Posts
Discussion Starter #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 ?
 

·
Registered
Joined
·
50 Posts
It looks to me like the rear pinion angle is not going to be good once the suspension starts articulating. Im no expert be I think your bars should be parallel or atleast close.
 

·
Registered
Joined
·
31 Posts
Discussion Starter #6
Hi guys,

I expect a little more comment from readers of this wonderful forum.
Please don't hold back any info/comment.

Thanx !!!
 

·
Registered
Joined
·
3,953 Posts
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.
 

·
Registered
Joined
·
31 Posts
Discussion Starter #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
 

·
Registered
Joined
·
3,953 Posts
#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
 

·
Registered
Joined
·
27,885 Posts
#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
#3. Why? Do you like a near or far IC and why?

For discussion, not questioning you.
 

·
Registered
Joined
·
3,953 Posts
#3. Why? Do you like a near or far IC and why?

For discussion, not questioning you.
The further back the instant center (IC) is the harder it is to keep anti-squat (AS) down, I suppose there is nothing wrong with his setup if you are going for a really high AS but I think most will agree that is not a good thing. I like to keep it to the lower side of the 60-80% range and shooting from the hip he would probably be somewhere around 130-150%. I was telling him to move the IC forward as a way of lowering his AS.

The rest of this is theory and discussion because I have honestly never really played with IC independent of AS. My setups land the IC somewhere around the front axle but it is a result of achieving the desired AS rather than deliberately placing it there.

#1 IC is your effective swing arm length and a short swing arm length would be more prone to unloading and driving the axle under the truck on climbs. For our application actual link length, link angle, and anti squat will probably play a bigger role but it is something to consider. Of course having those three things out of wack will cause a short IC so I suppose it is really the same thing.

#2 A short swing arm length can cause brake hop but I don't know how much that would really affect us in a low traction environment. Generally speaking if you have built your suspension around a fairly low AS and downward sloping roll axis angle you will probably not have a short enough swing arm length for this to be a problem anyway.
 

·
Registered
Joined
·
27,885 Posts
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?
 

·
Registered
Joined
·
3,953 Posts
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.
 

·
Registered
Joined
·
31 Posts
Discussion Starter #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.
 

·
Registered
Joined
·
3,953 Posts
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.
 

·
Registered
Joined
·
3,953 Posts
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
1418714753701.jpg
1418714765918.jpg



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

1418714788566.jpg

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.

1418714803976.jpg
 

·
Registered
Joined
·
31 Posts
Discussion Starter #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.
 
1 - 20 of 62 Posts
Top