Quick link suspension Q

DMiller

DMiller

Well-Known Member
Joined
May 4, 2014
Location
Charlotte, NC
I know a bit about suspensions independent of themselves, but now building a 3 linkF/4 linkR on a shorter wheelbase buggy, I am having trouble finding any information about how front and rear suspension work together... more so on the distance between the front frame mounted links and rear frame mounted links.

I hope this makes sense.

I've also seen a buggy with the rear links overlapping the front links...but I cannot seem to find the photo anywhere on the nets.

Thanks in advanced.
 
The front and rear suspension both have their own instant center and roll center, etc., and there are interactions there depending on the movement of those during suspension. There is also the whole vehicle roll center, instant center, etc.
It's all just projections of axis, etc., based on the pivots, heights, etc., and often the best geometry results from long link lengths, because there will be the smallest change in those parameters becsuse of the small anglular change of the links. Because everything is down to geometric projections, overlapping the link pivots is often not a problem at all because the resultants are the important part, not the links themselves.

Sometimes the whole vehicle roll center, etc., can move in strange directions or with very large velocities or accelerations with overlapped links though, or make some really strange behavior.

The answer is that it really depends on what the front and rear geometry is, where the resultants start out, where they move to, and how that movement interacts with the other end of the vehicle.

Clear as mud.
 
yes, clear as Lake Norman. (no, actually that's pretty good, thank you)

I was thinking there may be "guidelines" but after your explanation I see why that is practically impossible due to the all of the variables, and then the combination of the two together

My guess, the longer distance between the suspensions, the less dramatic each suspensions geometry effects the vehicle as a whole. So, with that said, the suspensions geometry may be more critical the closer together the actual links are.

Anyone have bad experience keeping their front and rear links tight together? Just curious.
 
Interestingly, the longer the distance between them, usually the more dramatic the effects because that would make the links shorter and therefore make the instant center, etc., generally move at a higher velocity and acceleration during suspension travel.

Really the only way to see what happens if the links overlap is to model the front (with one of the link calculators) and model the rear, and see where everything moves at each end during travel, and then see how they would interact.

I'm trying to wrap my head around how to spot conditions that would be bad, and I'm a little rusty with this stuff.. It could be that a 3 link and 4 link with solid axles are not complex enough to cause problems...
 
The more I think about it, the less of a problem I think it would be. Pretty much everything in side view (pitch center, etc.) deals with the instant centers, which are projections of the front and rear links, etc. The rear instant center is usually in front of the vehicle center in side view, and the front instant center is usually to the rear of vehicle center, etc. If you're just following the same projections by making the links longer, I'm not sure if there will be many problems with that at all.
 
Fabrik8 said:
Interestingly, the longer the distance between them, usually the more dramatic the effects because that would make the links shorter and therefore make the instant center, etc., generally move at a higher velocity and acceleration during suspension travel.
Click to expand...

Im picking up what youre putting down. If the only thing you were to change was the wheelbase, your pitch center would change along with others, even with the exact same suspension.

I guess I am baffled on short wheelbase rigs that do not use the full frame length potential when building a link suspension, especially if it would be beneficial.

And I still cannot find that one rig I saw awhile back that had crisscrossing front and rear links, I may have to give up on that one.
 
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