My Handling issues , figured it out after Summit Point

[DaveW]

As some of you have seen, I've been struggling with my Citation's handling since we modified the suspension after my Watkins Glen wreck in 2018, especially since we switched to the SCCA FC-spec Hoosier bias tires. We've been continually trying different spring rates, ride heights, damper settings, swaybar motion ratios in the rear, etc., etc., and some things got better, but others got worse.

At Summit Point, which I usually like, I threw a lot of changes at the car, none of which helped much, and some (before race 2) that made it worse. My times and race results throughout the weekend sucked.

I pride myself on getting my car working properly, but have been getting VERY frustrated with the lack of improvement. The situation was very confusing, and it was getting so bad that I, for the 1st time on the drive home, thought maybe it was my driving that was the issue and considered no longer driving in competition.

Monday, the day after Summit Point, I began seriously looking for design or mechanical causes and I finally identified the issue. There is an error in the front suspension geometry that hit me like a ton of bricks. It was so obvious that we (Steve Lathrop and I) should have never let it happen.

Luckily, it should be pretty easy to correct. So, again, we are looking forward to next season with FRP !!

[2BWise]

What'd you find?

[DaveW]

What'd you find?

The swaybar link attachment points to the bellcranks made the swaybar increasing MR (rate) in bump. The result is similar to the effect (understeer) of front increasing-MR-in-bump geometry. New bellcranks will correct it.

[DaveW]

The old (RH bellcrank photo) and new (opposite side drawing) are attached below.

[jtaphorn]

Dave says, "There is an error in the front suspension geometry that hit me like a ton of bricks. It was so obvious that we (Steve Lathrop and I) should have never let it happen."

OMG Dave, the rest of on the forum recognized the solution as so obvious that we didn't make the suggestion knowing that you would figure it out before to long.

Of course, that is my attempt at humor. You are illustrating the difference between the pros and the rest of us wankers. I am looking forward to your next driving impression after the change. Thanks for sharing.

[BeerBudgetRacing]

Sorry to try to educate myself at your expense....

The swaybar link attachment points to the bellcranks made the swaybar increasing MR (rate) in bump. The result is similar to the effect (understeer) of front increasing-MR-in-bump geometry. New bellcranks will correct it.

The old and new are attached below - the new one will be similar to the RH photo

It looks to me that this is the right bellcrank, dampers are behind (left in picture) and ARB is forward (right in picture).
So the swaybar attachment on the new one is the circled point.

On the old one, the attachment point starts moving both laterally and rearward and the further in moves the less lateral and more rearward movement - thus increasing the MR.

On the new one exactly the opposite happens because is starts with maximum rearward motion and decreases rearward movement and increases lateral movement thereby decreasing MR.

Am I understanding this correctly?

[DaveW]

Dave says, "There is an error in the front suspension geometry that hit me like a ton of bricks. It was so obvious that we (Steve Lathrop and I) should have never let it happen."

OMG Dave, the rest of on the forum recognized the solution as so obvious that we didn't make the suggestion knowing that you would figure it out before to long.

Of course, that is my attempt at humor. You are illustrating the difference between the pros and the rest of us wankers. I am looking forward to your next driving impression after the change. Thanks for sharing.

Having the front swaybar working properly will require some more setup changes, but at least, I hope, I won't be chasing my tail.

[DaveW]

Sorry to try to educate myself at your expense....

It looks to me that this is the right bellcrank, dampers are behind (left in picture) and ARB is forward (right in picture).
So the swaybar attachment on the new one is the circled point.

On the old one, the attachment point starts moving both laterally and rearward and the further in moves the less lateral and more rearward movement - thus increasing the MR.

On the new one exactly the opposite happens because is starts with maximum rearward motion and decreases rearward movement and increases lateral movement thereby decreasing MR.

Am I understanding this correctly?

I'm having trouble understanding what you are saying. Let me say it differently.

In both bellcranks, shown in full rebound, the radius to the pushrod is at a greater angle to the pushrod than the radius to the shock. So as the BC rotates under load, the pushrod angle to its BC radius has more rotation to bring it to 90-deg to its radius than does the shock. This means that the lever length of the shock force increases slower than the lever length of the PR, by definition this is decreasing MR.

The shock and the swaybar link are essentially parallel to each other.

So, in the revised BC, the shock pivot is on the same radius line as the swaybar, so they behave similarly.

In the original BC, the swaybar is on a radius line ~30-deg clockwise, so BC rotation CCW under load increases its lever length faster than that of the PR, making it increasing MR compared to the shock or PR.

So as the car rolls or goes into bump, the swaybar geometry acts like an increasing MR suspension geometry, and understeer results, especially under bump travel and gets worse with increasing roll angle.

This results in swaybar stiffness increase that under certain conditions, decreases understeer, because it decreases roll. It also means that softer front springs might be counterproductive, because they allow more roll and the swaybar MR increases. That's what makes it a confusing setup.

Clear as mud, right?

[BeerBudgetRacing]

Clear as mud, right?

I believe I'm understanding.

Looking at the VD Bellcrank the connections of the shock and sway links are at the same radius but at slightly different angles compared to yours at the same angle but different radii .

So the VD bellcrank will have the (although very slight) same condition you experienced
but you setup will require a stiffer ARB.

I think that is the definition of "compromise" in building/packaging these car.

[B17overhead]

One has to look at all link angles vs the pivot on both the pushrod side as well as the ARB side. The pushrod side linear bump motion has decreasing angular rotation of the bellcrank - The 90-degree radius (not the simple straight line point a to point b radius) to the pivot from the pushrod becomes longer which slows the belcrank rotation. So, to determine net change in ARB MR from the pushrod, one needs to look at both input and input rod angles and how they change vs the pivot in bump.