cant find some 4 link info (1 Viewer)

[BenMara]

Cant seem to find some info for the 4 link calc for a FZJ80 need the following
Vehicle Specifications:

Vehicle CG Height ? in

Front Unsprung Mass ? lb
Rear Unsprung Mass ? lb

Tkx

 

[pinkfloyddsotm]

i think for a rough estimation for COG you measure to the top bolt of the bellhousing.

unsprung mass is the suspension,diffs ,tyres and anything directly connected to them

sprung mass is the body,etc supported by the suspension.

 

[BellyDoc]

The top center bolt on the bellhousing is a decent first approximation for center of gravity, but there is HUGE variation when you actually measure it. If you want high accuracy, you measure.

Since you're proposing to re-do the suspension on your rig, the unsprung mass front and back is totally up to you. That's not a property of the original vehicle.

Unsprung mass is defined as that which isn't weighing down on the springs. This includes any weight on or directly attached to the axles themselves, and half the weight of the links you use (assuming a level link), since the link hangs on both the axle and the frame.

edit:

Additionally, and this is probably obvious, you need to be entering the value for the where the height of the center of gravity will be AFTER you do your new suspension/axles/wheels/tires, etc.

 

[BenMara]

ahh tkx Doc
yea startin to purchase parts for the swap. just tryin to do some research

 

[BellyDoc]

This is one of those topics, like some sort of college philosophy class, where the more you learn, the less you know.

I've achieved a state of near total ignorance on this topic. I have no decisive answers.

However... I'm beginning to understand the questions.

It's fascinating!

The biggest value of the 4 link calculator, for suspension newbies like me, is that you can play lots of "suppose" games really quickly and see some of the theoretical effects. For example, you can immediately see the changes in values of calculated results when you alter the positions of link attachments.

The biggest PITFALL, however, is that there is a lot of legend and not a lot of science in using these calculations to hone in on target values for the variables.

What I mean is that people talk about getting antisquat percent near such-and-such a value, for example. Then, they plug numbers into the calculator that include actual measurements, estimations, and wild-ass guesses. They then hone in on the link lengths and positions that get the target antisquat, and begin the build.

There are two problems with this. First off, the wild-ass guesses and estimations HUGELY affect the actual numbers after the build, and there is very little data relating ACTUAL measured numbers and performance characteristics for offroad vehicles. There is *some* data regarding track racing vehicles, but it has almost no bearing.

The second problem is that there are so many different activities that people call "4 wheeling" that it would be difficult to make generalizations about how appropriate recommendations are, in a general way.

For some perspective on how ambiguous many of the recommendations you might hear really are... check out this link to the closest thing I've seen to a treatment of the RESULTS of the link calculator. Rigs with videos of how they perform are compared with their modelling in the link calc:

4 Links by the Numbers

The result was that values that depart strongly from many of the recommendations you'd hear still perform very well!


Most importantly, though, I think there are several things that are crucially important in linked suspension design which are NOT captured by the link calculator. Now, I'm told that I have a dysfunctional copy of the calculator because Excel for Mac won't open some macros. Nevertheless, from what I understand, this is only part of a solution.

The fact is, the movement behavior of a linked suspension is subtle and complicated. It's very difficult to fully visualize and predict how it moves till you model the thing full size in 3D... basically build it with practice links and tack welds.

Many of the decisions about where links can go are limited by the available space. Within the range of possibilities, there are additional limitations if you want to control the ride height, the suspension travel, or the amount of roll steer. It very well may be that you'll have to choose to control one variable at the expense of others.

What I'm saying is that the link calculator is a starting point for a thought experiment. After that, you just have to cut some metal and mock the thing up.

Be prepared to do it and re-do it a few times before you finalize welds.

Don't be too upset if you have to cut away and re-do it, even fairly late in the game.

Be ready for it to take however long it takes.

 

[BenMara]

sounds like i need to get more parts here before i cant start lookin at suspension design

 

[Eskimo]

For some perspective on how ambiguous many of the recommendations you might hear really are... check out this link to the closest thing I've seen to a treatment of the RESULTS of the link calculator. Rigs with videos of how they perform are compared with their modelling in the link calc:

4 Links by the Numbers

The result was that values that depart strongly from many of the recommendations you'd hear still perform very well!

Actually, my takeaway from that is pretty consistent among the rigs that work well without water in the tires... AS between 50-75, but more importantly, an IC that's pretty far in front of the vehicle, and a decent (but not extremely high) roll center.

That's what I'm running as well (though my IC isn't as far out front as I'd like, but I've limited the vertical travel on the axle), and I can hammer down on climbs with confidence.