Does a bend in a link effect the geometry of the suspension?
 

Just want to put this up for discussion. I thought maybe the bend in a link can affect the squat/anti squat on our cars, some say it doesnt.

Here is some video I took with some extreme bends. I understand that we would not run this extreme of a bend on our cars but my point was to show that a bend can affect the squat/anti squat of a car.

Here are some videos I took last night. You can see in the two videos I took one with the bends pointing down, one with the bends pointing up. The shocks are fully compressed, as I would have expected when the bends point down, the shocks go to half travel when the bends point up, as expected.

In the middle of the vid you will see the camera move, this is where I am holding the car in the air and pushing down on the suspension to see if I can get it to settle.

Some other interesting observations:
I put these links on the lowers with the bend at the axle. I could not see any changes in the suspension.
I could not put the bends on the uppers at the axle due to clearance issues.
I need to put the bends on the lowers at the chassis to see the effects. I am assuming this is where I will see the lowers affected.

2014021_881555RESIZE_zps9af85fcc.mp4 Video by erikdye | Photobucket

20140120_205610_zpsff908ed2.mp4 Video by erikdye | Photobucket

Re: Does a bend in a link effect the geometry of the suspension?
 

Is anything binding in that vid?

If turning them one way creates binds then that would be an issue.

Re: Does a bend in a link effect the geometry of the suspension?
 

No.

Re: Does a bend in a link effect the geometry of the suspension?
 

Most of the time they won't (or not to a noticeable degree), but with some really sharp bends I could see it happening.

Re: Does a bend in a link effect the geometry of the suspension?
 

I could agree with that.

IMO, the videos show that a bend can affect the geometry. Since the bends are so crazy, its only good to show that it can affect it but its pretty unreasonable.

What I would like to know is where/when/if it does not affect it. For example, if you put a 5* bend at the axle it does not change it at all. If you do 5* at the chassis it changes it a touch, or maybe nothing happens until 20* etc,. Lots of questions.

I do know that those two vids change my suspension a lot. To get that much change in my car I would have to drop the uppers 2 or more holes to get that much change in a straight link. Dropping my uppers 1 hole is SIGNIFICANT and I cannot see a change in the shocks holding them in my hands, only when driving.

Re: Does a bend in a link effect the geometry of the suspension?
 

It think Jeremy did a great job of explaining why straight links work the same as bent links in Curt's thread.

Erik, think about when you have calculated the numbers for your suspension. To plot the intersect points you must know where the link starts and where the link ends. What happens in between those point has no significance because the push and pull happen in line with the end points.

Re: Does a bend in a link effect the geometry of the suspension?
 

Ok, if you say bends have no significance in the geo of the suspension, can you explain why there is a significant change in the suspension in the videos when the only thing changing is the bends in the links?

Re: Does a bend in a link effect the geometry of the suspension?
 

When you start adding tight bends like shown in the video, leverage becomes a factor and the way that force is transmitted will change.

Re: Does a bend in a link effect the geometry of the suspension?
 

I have nothing to add other than to ask if you could possibly find a shittier camera to film with next time. Maybe betamax or super 8 perhaps?








:flipoff:



I'm going to have to agree with duuuuuuuuuuuude on the leverage factor. I can't see it making much if any difference with a "standard" bend which I'd say is something under 15* or so but on crazy 30+ degree bends it'd be obvious.

Re: Does a bend in a link effect the geometry of the suspension?
 

I can't explain your video since I am not there to see what is affecting the rig. I am confident in math and proven physics though.

How would it change? The push and pull (the only two forces the link sees) happen from the same point. The vector is unchanged by the shape of the link.

Re: Does a bend in a link effect the geometry of the suspension?
 

Send Photobucket an email and blame them. I couldnt get it to load to their site normally so I had to do a go around. :flipoff:

If somebody could come up with a more scientific way to show the forces applied, I would like to see it. Like I said above, just because you cant see it and maybe not feel it does not mean it does not affect anything.

For you and anybody else who questions my method, why not do the experiment yourself? Took me about 10 min and 10" of all thread.

Re: Does a bend in a link effect the geometry of the suspension?
 

the only factors i can see with extreme bends is

1. they will change in length from pushing and pulling from uppper and lower links, or

2. interfere during travel because of pushing and pulling...

hard to see what you are showing, especially when the shocks are at such a steep angle with weak springs, not that your setup is bad, its just a sensitive suspension to test in that fashion.

Holding the rear axle is allowing any off center weight to affect your test. set the rig down and press and release the rig and see what happens.

on paper, bends make no difference, unless the factors mentioned are applied.

Re: Does a bend in a link effect the geometry of the suspension?
 

I agree. I should note that everything I have said above is assuming that no lengths or geometry changes.

Re: Does a bend in a link effect the geometry of the suspension?
 

Endpoints would be the same no matter the arc correct?

Re: Does a bend in a link effect the geometry of the suspension?
 

I think my terminology is wrong, however, I am willing to bet that there can be some lift/drop forces when the bends are tight as opposed to a straight link. It may not be much, but I bet its there.


I've also got an idea for a test setup. I'll post it in a few...

Re: Does a bend in a link effect the geometry of the suspension?
 

I should have added above, I cant see the links bending nor flexing.

What would you consider a better setup to test with? I would actually guess the more sensitive the better. Maybe take the springs off? Maybe stand the shocks up?

Would this model be hard to setup in CAD? I wonder if it would show similar results?

Between the two videos not a thing changed other then the bends. I didnt even take the links off, I just turned them around.

Re: Does a bend in a link effect the geometry of the suspension?
 

Did that screw the rod ends in or out changing the length?

Re: Does a bend in a link effect the geometry of the suspension?
 

Well I was just trying to say that if you take a straight link and bend it than the length changes which I turn changes the geometry. If the bent link is the same length and the straight link it replaced than nothing changes.

Re: Does a bend in a link effect the geometry of the suspension?
 

the major difference between a straight link, and an extremely bend link is,

the straight link does not change in length.

the bent link is now a spring, and unless you used precise bending technique, your springs are different even if they are the same length.

even with a precise bending technique, the springs would vary tremendously, especially with extreme bends.

Re: Does a bend in a link effect the geometry of the suspension?
 

Now my engineering expertise is in seismic rated industrial structural systems not suspension geometry but physics is physics and it should hold true here as well. Looking at the video it looks like you are picking the truck in in a way to load the rear axle in a way that would simulate the load the rear axle sees under acceleration. From a rotational mechanics perspective what is between the ends of the link isn't important, the geometry is defined by the distance between the connection/end points of the link. As long as the end to end link distances are the same the shape of the link is totally irrelevant to the arch the suspension will travel, at least until you start increasing the forces in the system. When loaded as under acceleration bottom link will be in compression while the top link will be in tension to counteract the rotation of the axle. While the forces at the ends of the link are the same with a straight link or a curved link, what is different is the stresses inside of the link itself. A straight bar in tension or compression is much stronger than a bent bar in tension or compression. Draw an imaginary line from the link and to the link end. The farther your link strays away from that line the higher stresses it will see. The higher the stresses the more the link will deform under load. The more the link deforms under load the more the design will stray from the performance of the pretty unloaded engineering drawing someone made. I can't see how just flipping a curved link upside down would change the suspension, but then again I might be missing something since this is the first time I've looked at the physics of a 4 link suspension geometry.