Rear sway bar rate - Where to start?

[MCMLXIX]

I know its hard to say what will work as many different cars are set up many different ways.... Every car also has a differnt purpose. My goal is a Daily Driver with an occasional autocross and if I'm lucky a chance on a road course. That means seating for 4 and a functional trunk with no roll cage. With that being said, I'll give what details I have about my setup and let me know what you think...

1967 Chevelle hard top.
Boxed and braced frame.
New poly body mounts.

https://static1.pt-content.com/images/pt/2009/11/DSC04840-1.jpg

Front:
ATS spindles.
SC&C LCA (modified for double shear lower shock mount)
SPD adjustable UCA
Varishock Quickset 1s
Custom double shear upper shock mount
550# coilover springs

https://static1.pt-content.com/images/pt/2009/03/DSC06678-1.jpg

Rear:
Moser 12 bolt
Currie adjustable UCA (Johnny joint / OE Rubber)
Currie tubular LCA (Johnny joint / Poly)
Varishock Quickset 1s - custom mounted on upper crossbar and axle tube (both double shear)
175# coilover springs


Now I may go with stiffer springs, but this is what I'm starting with. .
.
.
For the rear sway bar I will be running a splined swaybar. It wll be a Speedway Engineering hollow bar. I will be running steel arms with the 30* bend the get them higher / closer to the frame. They have some low profile pillow blocks with brass bushings that will bolt to the axle on a custom mount.

https://static1.pt-content.com/images/noimg.gif https://static1.pt-content.com/images/noimg.gif


The sway bar rate options are limited by the arms because I have to pick arms that fit etiher a 1" bar or a 1.25" bar. I only want to buy one set of arms. The 1.25" bars are offered in a few more rates but they start higher. Also I will have 10" long arms with the option of going to 12" for qucik adjustments, but thats about it because of my space restrictions with the chassis...


I have not picked a front bar yet but I will probably do something similar on the front...


Here is the chart from Speedawy : http://www.1speedway.com/swaybar385.htm


So the $64K question: What rate should I start with?

...

[silver69camaro]

I'd go 2.5 to 3.0 deg/G. To start, do the math of an existing "upgraded" sway bar to figure out what it's rate is, then find a bar that matches that rate with your arms.

By the way Stock Car Products has the same parts as Speedway for much less.

[John Wright]

By the way Stock Car Products has the same parts as Speedway for much less.
Hmm, that is good to know<files away for future reference>

[Rhino]

I'd go 2.5 to 3.0 deg/G.

I'm going to show my ignorance a little here... when you're speaking of G, what is that in relation to? The sum of the rear corner weights?

[John Wright]

https://static1.pt-content.com/images/noimg.gif https://static1.pt-content.com/images/noimg.gif







So the $64K question: What rate should I start with?

...

If you can only do one bar...make the rate adjustable, drill several holes along the length of those arms and then use the hole that balances the car for you.(farther out softens the bar, closer increases the rate)

[MCMLXIX]

I'd go 2.5 to 3.0 deg/G. To start, do the math of an existing "upgraded" sway bar to figure out what it's rate is, then find a bar that matches that rate with your arms.

By the way Stock Car Products has the same parts as Speedway for much less.

Matt,
I'm not sure I understand your deg/G either. The swaybar chart lists rates in pounds @ 5 degrees of twist...

I dont have a set of scales and the car is in little tiny pieces... so I cant really check corner weights....

Also I see the standard size seems to be 37 1/2 inches.... so here is the rate chart for that length of bar ... http://www.1speedway.com/swaybar375.htm

John,
I figured I would make it adjustable with 2, maybe 3 holes. I will have to figure out some type of bracket on the frame. Right now the crossmember is about 10" from the bar. So I am basing my choice of bar on that dimension....

Here is a mock up pick of where I want to run the bar... up tight under the diff housing... the round bar is supposed to be the sway bar and the other "stuff" was just to hold it in place....

https://static1.pt-content.com/images/pt/2009/11/DSC09304-1.jpg

https://static1.pt-content.com/images/pt/2009/11/DSC09302-1.jpg

https://static1.pt-content.com/images/pt/2009/11/DSC09307-1.jpg

[Jim Nilsen]

I talked to an Addco rep years back and he told me to wait on my bar until I knew my weight of the car at each corner and the distance apart for the ends,the mounts and the distance from the bar to the links. With these numbers they can get the correct bar the first time out out. I am not sure if Addco has what you are exactly looking for since I haven't been to their site for years, but I too am in need of a bar now and have all of the info they asked for.

To me it is worth talking to a proffesional about what it is you need exactly instead of guessing. The cost of the bar is one thing but the cost of free engineering is priceless when it comes to getting the right parts the first time.

[JRouche]

Hey Rich, I feel yer pain :) I was in the same boat a earlier this year. I used the SWE splined bar. What I really wanted was just a ball park number. Lbs/In for 5* of twist for any after market bars. I looked high and low and never saw them expressing it in Lbs. but only in bar diameter. Didnt help me much.

I think I came up with my number from an example of one car I found.

So with my arms and the bar I used its 295lbs at 5* of twist. It may be a lil high, but my roll center is a lil low and my car is a lil top heavy. And the bars are only 90 bucks so I can swap it out if I need to. JR

Here is a lil showing on how I mounted mine up if interested. Page two shows the bar..

http://www.stevesnovasite.com/forums/showthread.php?t=121172

[The WidowMaker]

im at ~300lbs with my speedway frame mounted bar. im running about a 10" RRCH and a 1.5" hollow speedway bar up front. the suspension calculator i ran it through said that this combo would have slight understeer, but if i changed things a little it would tell me oversteer. its the best i could do for a balance. the calculator may be off though, since i had to come up with corner weights which i didnt have access to. i used numbers that i found on the chevelle site.

i dont have the stock rear crossmember anymore, but could you fab up mounts that would place the bar on the uca crossmember above the uca's? thats where i put mine, but like i said it isnt stock anymore. the 37.5" bar was just narrow enough to place btwn the frame rails, and the end links mount to the housing directly in front of the coilovers. this allowed the most clearance btwn it and the exhaust.

Tim

[silver69camaro]

Degrees/g is body roll in degrees per 1g of lateral force, typically referred to as "roll gradiant".

[Rhino]

If someone was wanting to calculate that value in in/lbs, and test to find the correct bar, would you apply your lateral force at the CG height and measure the force at roll center height?

[MCMLXIX]

OK.
Well I ordered a 37.5" hollow bar in .120 wall that will give me ~322# using 10" on the arm length. If I go to 12" on the arm I reduce the rate to ~268#.
These are @ 5 degrees of twist. I used the 30 degree steel arms to raise the mounting point closer to the frame and clear and road hazards.

https://static1.pt-content.com/images/pt/2009/11/DSC09526-1.jpg

https://static1.pt-content.com/images/pt/2009/11/DSC09530-1.jpg

[JRouche]

OK.
Well I ordered a 37.5" hollow bar in .120 wall that will give me ~322# using 10" on the arm length. If I go to 12" on the arm I reduce the rate to ~268#.
These are @ 5 degrees of twist. I used the 30 degree steel arms to raise the mounting point closer to the frame and clear and road hazards.

Sweet, yer on yer way. You prolly see it already but I think the pillow blocks are directional. Im not sure if that is the intention but they look like it to me.

The bronze bushing hangs out a lil further on one side. I think that side should be placed against the collar.

Also, its not much work but I think helps to put in some method of greasing them. I drilled and tapped for zerk fittings and grooved the bushing. If you do I would groove in a spiral and NOT all the way to the edge. Otherwise the grease will just flow out the ends and not keep a nice lil pressure of grease in the channel.

One last thing. Place the mounts carefully. So there isnt any sideways bind. As perpendicular to the frame as you can get it. After bolting up the mounts, and being supper careful with alignment both my front and rear bars had a lil grab to them, even with a full load of grease. And I mean just a lil grab. So the bar would hold its posision with the arms disconnected from the links. It only took a slight finger pressure to make it move, but it was a concern. Get it as square to the frame as you can. JR

Some pics.

https://static1.pt-content.com/images/pt/2009/05/c-2.jpg

https://static1.pt-content.com/images/pt/2009/05/d-2.jpg

https://static1.pt-content.com/images/pt/2009/05/b-2.jpg

A shot of the lil holder I made to support the bar with the floor jack so I could align the mounts easily.

https://static1.pt-content.com/images/pt/2009/05/e-2.jpg