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Anybody running more seperation at the frame than the axle?

2K views 19 replies 8 participants last post by  shelljeep 
#1 · (Edited)
Switching to a 4 link suspension soon and I'm shooting for low antisquat numbers.
The design I have come up with has slightly more seperation at the frame than the axle, popular opinion says to run more at the axle.

Popular opinion used to say "Never mount your lower link mounts above axle centerline" either but take a look around us since rockracing hit. It's very commomn to see people running their lower link mounts near the top of the axle tube, gives a flatter link angle for better geometry and also gets it up out of the way.
I'm just wondering why everyone says more at the axle, less at the frame, even if it suits your needs.

Other than the link mounts on the axle side seeing slightly more strain, what are the drawbacks?


ed.sp
 
#2 · (Edited)
Popular opinion used to say "Never mount your lower link mounts above axle centerline"
The only people that used to say that either heard it from someone else or didn't understand physics.

shelljeep said:
Other than the link mounts on the axle side seeing slightly more strain, what are the drawbacks?
Instant center, for one. Doing that throws the instant center out in front of the vehicle, so the axle might rotate back slightly under compression. This can make it harder to climb stuff because you'll have less tractive force at the front wheels - having the instant center behind the axle forces it into whatever you're climbing.

It's also hard to say without seeing exactly how you'll have it set up, but I'd guess you'll have some really weird changes in AS throughout travel by having it set up that way too.
 
#3 · (Edited)
Instant center, for one. Doing that throws the instant center out in front of the vehicle, so the axle might rotate back slightly under compression. This can make it harder to climb stuff because you'll have less tractive force at the front wheels - having the instant center behind the axle forces it into whatever you're climbing.

It's also hard to say without seeing exactly how you'll have it set up, but I'd guess you'll have some really weird changes in AS throughout travel by having it set up that way too.
I'm not sure if I'm understanding how instant center can do that, I'm sketching some stuff out right now to try to figure what you mean by that.
I should add that another reason I drew it up with more sep at the frame was that it also helped me to shape the roll axis so that the tires would move forward slightly as they compressed. I felt like that would help the tires climb. Your thoughts?
edit: The instant center is 177" in front of the vehicle. When I said slightly more sep, I meant 1.25".

Would it help to show you a screen shot of the design in Triaged's Excel calc?
 
#5 · (Edited)
Instant center height is 2", roll center height is 21".
Back in a sec with the screen shot and some more details.
edit: Here's that screen shot-

The links are fairly short, mainly due to packaging concerns. Trying to allow the axle to tuck up in front of the engine when it compresses.
Here's a link to a thread with some more details if you wanna take the time to read thru my rambling first post.
http://www.pirate4x4.com/forum/showthread.php?t=588893
 
#6 ·
I am assuming this is a rear suspension. nothing magic happens when the instant center is behind the axle center line instead of in front of it. lust like you said it is a way to get less anti squat with whatever lower link configuration fits. The real drawback is how the antisquat changes with suspension travel.

I would like to have 0% anti squat at full droop and 100% at full compression and around 70% at ride height. with parallel equal length links, it works the opposite of with more AS at droop less under compression.

The way to design a suspension that has the desired AS curve through the travel is to make the upper link shorter than the lower link and then position the links so the instant center at ride height is somewhere above the front axle, but the instant center at full droop is behind the rear axle essentially on the ground. The thing you have to watch out for when you dot this is what you are doing to the U joint angles. Usually with a lot of travel you can't have as steep of an AS curve as I described and keep the ujoints happy.

anyway this is just an example of instant center behind the vehicle being very common and working well.
 
#9 ·
It's a front suspension, but the rear design has more seperation at the frame than the axle also.
I made the uppers slightly longer just because of the ujoint issue, I will look at the design with your info in mind. I'm not committed yet, the frame is cut, the parts are bought, but I haven't built any brackets.
As for the 3 link w/panhard, I was fooling around with that calc today actually. It looks like I can get the same roll axis and A/S with that design and probably have better options for fitment.
Thanks for the info from both of you.
 
#12 ·
Don't over think the front; the best thing that you can do is make shur nothing binds you don't have a lot of axel steer and nothing rubs; and then hook your winch line up to your front axel and suck your front end down on big clims. This will take out any bad design in the front end and will make it clime better than anything you can acheve with good design. I'm not saying to just throw the front end together; put some thought in it just don't get carred away with it. Put your time in the back end and learn to use your winch for the front. Some of us in our club have spent hours working on the front end links and it makes littel to no diffreance as the guys that have realy bad front link design clime just as well or better as every one else dos as soon as they use there winch. Spend your time on the rear links; its time well spent.
 
#13 ·
Some of us in our club have spent hours working on the front end links and it makes littel to no diffreance as the guys that have realy bad front link design clime just as well or better as every one else dos .

*cough* Barry *cough*

:D

Listen to this advise.
 
#18 ·
Shit, don't sweat it, that's entertainment.:laughing:

Thanks for chiming in there Eskimo and 2D. I didn't mention it in this thread I don't think, but I'm planning to relocate the winch to in between the radiator and motor to help center my weight bias and so I can use it on the axle.
 
#19 · (Edited)
We don't eather we just use some pullys or a pice of tubing to run the winch line through to the front axel; some of use use a seprate pice of winch line and run it up to the winch. Trust me you will be suprised at how much you will use it once you do this; it makes a huge diffrence in climbing when you can suck your front end down. Edit; sorry I miss read you last post.
 
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