Preloading Sway Bar

[Grant 302]

And not sure what was said above, as it confused me slightly, but lengthening the end link will apply more weight to that corner.

Kelly, Are you 100% sure about that? Does the same apply when the springs have more rate than the sway bar?

For every inch unloaded from the spring on the driver side, the rate is 'borrowed' from the other side at inverse of the two rates (bar + passenger spring) added together (softer than the front spring rate). Or at least that's the way I understand the math.

 

[ArizonaBOSS]

Kelly, Are you 100% sure about that? Does the same apply when the springs have more rate than the sway bar?

For every inch unloaded from the spring on the driver side, the rate is 'borrowed' from the other side at inverse of the two rates (bar + passenger spring) added together (softer than the front spring rate). Or at least that's the way I understand the math.

Someone want to draw out a free-body diagram?

Or just do a quick experiment next time the car is on scales?

 

[JScheier]

For every inch unloaded from the spring on the driver side, the rate is 'borrowed' from the other side at inverse of the two rates (bar + passenger spring) added together (softer than the front spring rate). Or at least that's the way I understand the math.

Correct. Lengthening or shortening the end-link beyond zero results in preload.

 

[twistedneck]

Since you are talking about sway bar pre-load: I was told by Sam Strano that the front sway bar OEM mounts grab the bar tight and adds some resistance to suspension movement. I have not had the chance to get on a track or even AutoX after switching to his adjustable front, so I don't know if I will get noticeably more nose movement or not. I did notice that it seemed to be a bit pre-loaded (evenly both sides) with the suspension loaded. I did notice on a hairpin right turn that I had much less push with even a light passenger on the OEM bar and staggered tires.

I realize most of you discussing this thread are probably not on the OEM bar, but I figured this was worth mentioning if you still have a stock suspension otherwise. I am wondering if anyone has noticed better articulation in the front with the OEM mounts replaced for something that does not impede movement.

OEM front bars are bonded to the stabar, they slip a little against the outer brackets and lower sled plate. that's why the paint in the upper bracket has Teflon inside of it $$ to get rid of noise and address preload issues during build. like it was stated they have some stiction if you deflect the bar really far like during install.

if you lower the car the bars are wound upward against the bushing and after a while it will take a set in that position and act normal again - partly due to wear and Mullins effect, dirt, etc. supposed to offer up a lot of on center feel but adds rate - about 5-10% depending on how stiff the rubber and brackets. So that throws a total extra spring in the mix called parasitic rate and I would eliminate them and replace with nylon / Delrin if it were a full race car.

 

[BMRTech]

Kelly, Are you 100% sure about that? Does the same apply when the springs have more rate than the sway bar?

For every inch unloaded from the spring on the driver side, the rate is 'borrowed' from the other side at inverse of the two rates (bar + passenger spring) added together (softer than the front spring rate). Or at least that's the way I understand the math.

HA! I was.....lol

I actually don't know what I had on my mind when posting that. Not sure if it was the testing and development I just did on the S550 bars, rear in particular...or if it was the new bars we are testing for the '79-'04 platform. No clue.

So that said, I do have some info. I had a few minutes to do some very quick testing on one of our S197's that we have outfitted with our handling inspired parts, and that includes our 38mm Bar and Adjustable End Links.

Long story short, as the car was set-up....it was at 27.25" ride height up front.

LF (driver) side weight was 1063lbs

Lengthening the driver side to 11.375"....and keeping the passenger side at 10.625" resulted in a LF (Driver) side weight of 1020lbs.

The LF (Driver) ride height dropped 3/16" in this position, and the RF (pass) side raised up 1/4".

Moral of the story, lengthening the driver side end link resulted in a 3/16" drop in ride height, and a loss of 43lbs.

 

[DGRacing]

HA! I was.....lol

I actually don't know what I had on my mind when posting that. Not sure if it was the testing and development I just did on the S550 bars, rear in particular...or if it was the new bars we are testing for the '79-'04 platform. No clue.

So that said, I do have some info. I had a few minutes to do some very quick testing on one of our S197's that we have outfitted with our handling inspired parts, and that includes our 38mm Bar and Adjustable End Links.

Long story short, as the car was set-up....it was at 27.25" ride height up front.

LF (driver) side weight was 1063lbs

Lengthening the driver side to 11.375"....and keeping the passenger side at 10.625" resulted in a LF (Driver) side weight of 1020lbs.

The LF (Driver) ride height dropped 3/16" in this position, and the RF (pass) side raised up 1/4".

Moral of the story, lengthening the driver side end link resulted in a 3/16" drop in ride height, and a loss of 43lbs.

Kelly, how did the passenger side weight change? Or it didn't? I assume that 43lbs moved somewhere else.
Would one want to adjust their coilover height on driver side up 3/16" to compensate? Or does that add the weight back?

Someone want to draw out a free-body diagram?

Or just do a quick experiment next time the car is on scales?

Drew, I will be able to do this sometime in April when I get my alignment "shop" set up in bay 2 (of my garage. lol).
Since I have the ranger quickjack, raising the car, making quick suspension adjustments and lowering back on scales is fast. Can do a lot of experiments then.

 

[twistedneck]

HA! I was.....lol

I actually don't know what I had on my mind when posting that. Not sure if it was the testing and development I just did on the S550 bars, rear in particular...or if it was the new bars we are testing for the '79-'04 platform. No clue.

So that said, I do have some info. I had a few minutes to do some very quick testing on one of our S197's that we have outfitted with our handling inspired parts, and that includes our 38mm Bar and Adjustable End Links.

Long story short, as the car was set-up....it was at 27.25" ride height up front.

LF (driver) side weight was 1063lbs

Lengthening the driver side to 11.375"....and keeping the passenger side at 10.625" resulted in a LF (Driver) side weight of 1020lbs.

The LF (Driver) ride height dropped 3/16" in this position, and the RF (pass) side raised up 1/4".

Moral of the story, lengthening the driver side end link resulted in a 3/16" drop in ride height, and a loss of 43lbs.

makes sense, the more you make the bar horizontal the less spring rate it can offer since the arms get longer. longer lever arm = less bar load.

 

[BMRTech]

Darren, I did not have a lot of time.....but off memory.

Links same = 1063 LF / 1008 RF

Driver Lenthened = 1020 LF / 1052 RF

I am fairly certain this is what happened....if anything, the RF may have been 1042 and not 1052....but, I am pretty certain it was 1052.

 

[blacksheep-1]

Good info but I still think loading a sway bar to transfer weight is a crutch and should only be done when all else fails.

 

[BMRTech]

Agree 100%

 

[DGRacing]

Darren, I did not have a lot of time.....but off memory.

Links same = 1063 LF / 1008 RF

Driver Lenthened = 1020 LF / 1052 RF

I am fairly certain this is what happened....if anything, the RF may have been 1042 and not 1052....but, I am pretty certain it was 1052.

You're awesome for doing this for us!! Thanks man.

And this is what I was originally thinking. Your point about using weight is well noted too. But I'm already carrying around two fiddy (6'4" here!). Can't be adding 250lbs of ballast on top of that!

 

[DGRacing]

Good info but I still think loading a sway bar to transfer weight is a crutch and should only be done when all else fails.

Does the car know the difference though? The scales read what the scales read. The physics is the same?
But I can see where artificially moving weight can affect another dynamic negatively compared to adding weight. Although, the added weight has its own penalty too.
No free lunch here!

 

[Grant 302]

Kelly, thanks for the confirmation and data!

Does the car know the difference though? The scales read what the scales read. The physics is the same?
But I can see where artificially moving weight can affect another dynamic negatively compared to adding weight. Although, the added weight has its own penalty too.
No free lunch here!

I think there are differences. As the car transitions to unload the bar, I'd expect there to be some differences in how he car feels and 'loads' at say the limits of traction. Compromises that I'm sure the more experienced allude to.

That said, if you'd post up your front sway, spring rates f&r, and your uh, race weight ...I'd like to take a stab at figuring out your theoretical adjustments.

 

[DGRacing]

Kelly, thanks for the confirmation and data!
I think there are differences. As the car transitions to unload the bar, I'd expect there to be some differences in how he car feels and 'loads' at say the limits of traction. Compromises that I'm sure the more experienced allude to.

That said, if you'd post up your front sway, spring rates f&r, and your uh, race weight ...I'd like to take a stab at figuring out your theoretical adjustments.

This off the top of my head but fairly close. Front sway is 36mm. Rear sway is 25mm. Car is 3350lbs as is with 1/2 tank of gas. 3600lbs with driver. Front springs 800lbs, rear 400lbs. Front ride height 27" to fender apex from ground. Rear is 27.50". You probably don't want to factor the tire spring rates at this point. They're a 680 sidewall. Much stiffer than Hoosier slicks.

 

[Grant 302]

What brand is the front sway bar? If it's adjustable, what position?

EDIT:
Sounds like Eibach? I assume middle position = 400 lb./in.

 

[Grant 302]

Okay Darren, I *think* I have the theoretical adjustments to compensate for your weight assuming the center position on an Eibach front bar.

Start with the car level/not leaning left/right and the rear springs set to the same height. Pre-load front bar by lengthening the driver side link (and/or shortening the passenger link) by a total of 0.45 in. Lower the front passenger side by 3 full turns (assuming 10 thread/in. which I think is standard) for a total of 0.3 in.

I think that should get you close...looking forward to your data when you get your scales set up!

 

[DGRacing]

What brand is the front sway bar? If it's adjustable, what position?

EDIT:
Sounds like Eibach? I assume middle position = 400 lb./in.

Ding ding ding! Nice guess.

 

[DGRacing]

Okay Darren, I *think* I have the theoretical adjustments to compensate for your weight assuming the center position on an Eibach front bar.

Start with the car level/not leaning left/right and the rear springs set to the same height. Pre-load front bar by lengthening the driver side link (and/or shortening the passenger link) by a total of 0.45 in. Lower the front passenger side by 3 full turns (assuming 10 thread/in. which I think is standard) for a total of 0.3 in.

I think that should get you close...looking forward to your data when you get your scales set up!

Grant. That is fantastic! You are now my honorary "team engineer"!

It will be awhile before I can test this. Car is just a pretty "roller" right now. But if I recall correctly, the adj. endlinks I had on there before were fully retracted so not sure it will be possible to shorten them. I'm switching to the steeda comp ones. But I've been thinking of cutting them down a half inch so I can shorten them.

The other thing is that the swaybar link arms sit right on top of the A control arm when level and loaded. Can you alter your equation to lever just one side of the swaybar, shorter?
Will have to see how much they can "move" down. This is because the car is very lowered I think. I will post some pics.

 

[Grant 302]

As long as the passenger side is 0.45 in shorter, that's what makes the difference. The main three things that would change the adjustments would be driver weight, front spring rate, and front sway position/rate.

You should do whatever you need to to get the bar as close to level as possible.

Now go win some races, so I can put that on my resume!

And as Drew suggests, for anybody who understands how to draw free body diagrams...it's the only way to make *any* sense of all the reactions. Better than itsy-bitsy and muttering to oneself. :-[ :