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Thread: Beam Suffering

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Posts: 61-70 of 117
2012-07-29 18:16:57
#61
Basically you want the moment of the suspension locating devices (roll center) to be close to the c of g. In the b14 case the rear c of g is right about axle level thus keeping the roll center close reduces the roll couple (which is the distance between the c of g and roll center). On cars that don't have good trailing arms (like a live axle rwd with leaf springs) a watts link works wonders over a panhard bar bc that axle moves all over the place. The only problem we really have is the roll couple being too big thus for the b14 a panhard tends to be a better choice. Plus it's much easier to fabricate
2012-07-29 23:15:04
#62
Another little update on overall suspension. I'm really loving the ES bushings and the Addco on fully stiff. The road NVH only slightly increased, but the car control is amazing. I took the same downhill s turn, wasn't trying to go fast (trunk had a brand new battery for the B15) and cake in the car (don't want to damage the cake you know!)

I hit 45mph and didn't even notice it. It felt smooth and like I was going the 25mph speed limit. I asked the wife if she remembers when I took that turn and it felt like the car was gonna flip over, well I am going about the same MPH.

TheSam call it right:

Originally Posted by TheSam
Do you have rear trailing arm poly bushes? They make a HUGE difference to the car.

-Phone-

Originally Posted by TheSam
Fit the trailing arm bushes before you go into all this, honestly the difference they make is incredible.




Originally Posted by hammerin

How much of a bitch was that to press in? Same as the front control arms?


It was stupid easy. I was able to press them in with my bare hands. It's either because P11 holes are bigger, or rear bushings need some play.

Originally Posted by hammerin
Just to get the creative juices flowing, here's a picture of the Chevy Cruze watt setup:






In case you're lost, the watts setup is oriented behind the axle on the Cruze. So in the picture, pretend we're looking from the front of the car to the rear.

Perhaps we need to raid the Chevy parts bin? hehe


That's actually how I was considering building a Watts setup. The thing is, after reading 2JR's thread to the end, I saw that they still went back to a Panhard since it was a lot simpler and the benefits where neglectable.


Originally Posted by nissanboi
The only problem is the watts link is a far superior axle locating device than a panhard bar but the roll center of a watts link is still way above the axle so you are not reducing the roll couple that much from stock. The panhard bar on the other hand you can adjust the roll center to be just below the axle giving a very tight roll couple (more stability in a turn) and for our chassis reducing the roll couple is much more important than the axle moving a negligible amount more when we turn one direction versus the other.


This is why I would also consider mounting the watt's on the beam. But then you run into ground clearance issues.


Originally Posted by wes
I stand by that te Stillen rear bar is the way to go. In addition the movement in the bushings is engineered in to the entire package. I preferred my car with OEM bushings to the solid super pro bushings back there. This on a 2300 lb B14 with me in it, r compounds, Koni 8610's, and a dedicated track car.

I also think you are going to spend all of this time on the rear beam only to find there is more to be had out of a better damper and spring combo.


I have a Stillen bar on my B15, I was very tempted to remove it and try it on the P11. Though it sounds like it's a few inches short. Interesting enough the Stillen doesn't even attach to the back of the beam, it's way infront of it.

Originally Posted by hammerin

I guess I really don't understand how a watts setup raises or lowers the roll center/roll couple then. To me it's just 2 panhards tied together.


Look at were the Watt's is mounted at on the body itself. That's what determines the roll center. If you can get a watt's real low this would fix the issue, but then you start having ground clearance issues with the arms.
Last edited by Vadim on 2012-07-29 at 23-20-01.
2012-07-30 00:21:28
#63
Amazing what happens when you stiffen the end that is not doing a damn thing in a corner, isn't it? (I am referring to the rear end but of course)

Remove front sway bar end link, naow. Don't replace bushings, just remove an end link and push the car. I still have yet to do that on my car!!!!!

IRS > Beams
Last edited by Kyle on 2012-07-30 at 00-22-03.
2012-07-30 05:40:20
#64
Originally Posted by nissanboi
Basically you want the moment of the suspension locating devices (roll center) to be close to the c of g. In the b14 case the rear c of g is right about axle level thus keeping the roll center close reduces the roll couple (which is the distance between the c of g and roll center). On cars that don't have good trailing arms (like a live axle rwd with leaf springs) a watts link works wonders over a panhard bar bc that axle moves all over the place. The only problem we really have is the roll couple being too big thus for the b14 a panhard tends to be a better choice. Plus it's much easier to fabricate



Originally Posted by Vadim

Look at were the Watt's is mounted at on the body itself. That's what determines the roll center. If you can get a watt's real low this would fix the issue, but then you start having ground clearance issues with the arms.


Okay. I think I'm getting it. The higher the end links the more it wants to rotate (roll) the chassis. Which in turn unloads the inside tire. Less rubber on the road = less grip.
2012-07-30 19:07:23
#65
boss
2012-07-30 19:32:00
#66
Originally Posted by hammerin
[Okay. I think I'm getting it. The higher the end links the more it wants to rotate (roll) the chassis. Which in turn unloads the inside tire. Less rubber on the road = less grip.


You are almost there Hank.

Think of it like this,

Picture the side of the car

Now picture a point about 4" off the ground at the front axle and a point about 12" off the ground at the rear axle.

Now draw a line between those points.

That is the axis that the body of the car wants to roll around as it goes through the corner.

Now imagine how that car looks from the back end as it rolls around that line.

Yes, a tire that is not in contact with the road offers no traction, but that is not really what is happening in this case. It is actually just the opposite. Because of the angle of that imaginary line, the car ends up placing a tremendous amount of load on the outside front tire. Becasue of this, the outside front tire will reach and exceed its limit sooner as it is being forced to do more work. Then your car goes plowing straight off the track!

Now picture the same car but with the point at the rear axle at the same 4" off the ground. Perhaps even 3.5" off of the ground.

Now how does the car look when it is going around the turn?

Let me just say from personal experience that it is a big difference.

The 4" and 12" numbers I gave are for an example only. I do not know where the actual roll centers for the B-14 are located. I just wanted to give a simple example of what a difference lowering the rear roll center can make.
2012-07-30 19:48:49
#67
12" is correct for the rear. Here is what 2JR said. They obviously have a modified LCA to get -2" up front.

Originally Posted by smokinjoe
Put me on the low end of that curve! Our roll centers are +12 (rear) and -2.. can you get more jacked up than that?!


I would even say, if we can lower the roll center of the SRL link, it would be sufficient enough imo.
2012-08-02 20:55:04
#68
I notcied something else while putting in a B15 link on my car this week. the SRL has on over-center point as it sweeps through the range of motion. Meaning that there is a kinid of natural center location and as you go up or down from there it swings the axle and eventually induces bind. I would think with enough spring or swaybar you could mitigate that effect, but it's still there. The other thing worth noting is that if you're lower (or higher) than stock height, you're already locked to one side of the SRL and it seems to make it tougher to move it past the over-center position.

Either way the PHB set up would be the best fix for this. Making the SRL adjustable to deal with that would be way more trouble than it's worth.
2012-08-04 20:10:10
#69
i've already bought an adjustable srl for the panhard and it wasn't difficult to fit and allows you to re centre everything at whatever your chosen ride height
2012-08-14 09:57:08
#70
Originally Posted by happyharrysco1
i've already bought an adjustable srl for the panhard and it wasn't difficult to fit and allows you to re centre everything at whatever your chosen ride height



I really don't see how the adjustable dog bone really does anything. If you don't change the length of the entire assembly, it's still going to bind when it goes past center while on its arc travel.

For those that are lost, I'm referring to the main SRL attachment point on the beam, not the dog bone attachment point.
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