How to design a sway bar w/ 3link + watts linkage

[BANKO]

How does one properly design a sway bar paired with a 3 link + watts linkage to not induce bind? I thought the primary advantage to a 3 link was the lack of bind. I have seen AME's 3 link rear clip has a small diameter sway bar. Also, what are the design advantages of a splined sway bar for the rear axle over a conventional formed sway bar?

[The WidowMaker]

splined bars allow for easier packaging since you can get custom lengths and arms. the only real advantage is that you can swap bars to change the rate. splined bars are around $100 ea (for just the bar), and custom non splined bars are ~$400 from what i have seen. if youre going to be swapping bars for different setups and putting it in a non stock mounting place, then splined wins.

[James OLC]

Hellwig has a 5-position 1" solid adjustable sway bar that works with the Lateral Dynamics 3-link and watts setup. It's called (I kid you not) The OneLapCamaro Bar (really - it is).

[JRouche]

Originally Posted by The WidowMaker

splined bars allow for easier packaging since you can get custom lengths and arms. the only real advantage is that you can swap bars to change the rate.

Your first advantage for the splined bars was packaging. The easy to change rates are another, but not the only advantage. I needed them more for packaging. I have a very tight (space) rear section, alot of links. The packaging that the splined bar affords was a BIG advantage. My rear section is mostly modified aftermarket pieces. So there was no such thing as looking through catalogs for a formed bar.

I have splined bars on the rear and front.

Just recently got to take the car on its first drive, after 15 years of messing around. Oh man!! Lemme say, without any tuning of the suspension, not even a tweak of the adjustable shock valves the car is a flat turning car.

And this was only on semi high speed turns, 80 mph highway turns (in a 55mph zone). She was as flat as some of the better cars I have driven.

I havent pushed it on any tight turns yet, I dont have a course to go to. I want to get used to the feel of the car before taking it to the extremes.

I like to feel a car out on an open flat track to find out where the breaking point is. Where the tires break loose so I can get an idea of how its gonna react. I wont do that on the city streets. Limit testing HAS to be done on a closed track with no cars or hard curbs.

But so far I see the air ride suspension being years ahead of the 48 year old stock suspension.

Im gonna put 300 miles on the car then bench it. Ill raise it up two feet on stands and check EVERY suspension fastener and inspect the suspension for any odd wearing or rub marks.

Once I know she is still tight I will find a track and try to loop her. Yes, on purpose, just to find the break away point. I want to feel the limit of grip. If she doesnt break away before I reach my speed limit then Ill still be happy. But Id like to at least get a feel for when she breaks.

At this point I dont know if she is pushing or light at the rear. I havent been able to feel any of the extreme suspension handling yet. I have taken it trough some semi sharp turns on light throttle and it seems to be on the side of oversteer, no pushing at all.

But thats the tendency you have to be VERY careful with on the street, oversteer. A heavy, pushing car will give you more indication of traction loss before you get into trouble. An over steering car will feel great, almost too fast till she breaks free at the back side at the last second. NOT fun on a city street. Lots of fun on a track with enough HP, you have enough room to recover and throttle her back into the lane

Solly, I got side tracked. Umm,, I like splined sway bars. JR

[exwestracer]

Originally Posted by JRouche

But thats the tendency you have to be VERY careful with on the street, oversteer. A heavy, pushing car will give you more indication of traction loss before you get into trouble. An over steering car will feel great, almost too fast till she breaks free at the back side at the last second. NOT fun on a city street. Lots of fun on a track with enough HP, you have enough room to recover and throttle her back into the lane

Solly, I got side tracked. Umm,, I like splined sway bars. JR

If you combine a low rear roll center with a big bar, it's a little wider "sweet spot" (to control that breakaway) than you'd get with more roll center and less bar...

[JRouche]

Originally Posted by exwestracer

If you combine a low rear roll center with a big bar, it's a little wider "sweet spot" (to control that breakaway) than you'd get with more roll center and less bar...

Yup. I dont know about a wider sweet spot, Ill take your word for that.

But I did drop my RRC pretty low with the watts link so I opted for a stiffer roll bar out back.

What I see it giving me is more control over the adjustments. Now I have a roll bar that can be tuned to the low RRC. And I can change the RRC height with one bolt, I have about 6 inches of room for adjustment there.

So combining the adjustable RRC height with the adjustable roll bar rate I can either get into some real trouble or find a nice combo of settings to make for a car I want to drive FAST.

The guessing part for me was in the rate for the roll bar. I was kinda shooting in the dark. But I think I got it close, actually on the weak side of where I wanted it, which is odd cause its a pretty stiff bar for the car (I forget but I think its right around 300lbs for 5 degrees of rotation).

I might play with the RRC height before adding more bar stiffness, cause well, its free rear end stiffening, and that was the purpose of having an adjustable RRC height.

If I cant get what I want from adjusting it I can easily swap out the straight torsion bar for a stiffer one, they are ninety bucks. And the bar is pretty stiff, for the type of car. I might just have too low of a RRC height.

I wont mess with the front, I think its got a great bar in place and its controlling the front just fine.

I feel the rear being a lil "slow" if that means anything. For me a fast rear is kinda ahead of the front for turn in, "stiff" or "fast". Dont know how to splain it.

I want it to be a lil faster to react on turn in so its at least responding to the turn as fast as the front or even a lil on the faster side.

Sounds weird but with fast driving I like to see how the rear is responding before the front. If I have confidence with what the rear is doing I can take the car faster through the turn. I NEED to feel what the rear end is doing. And for me that means alot of oversteer and a somewhat touchy rear end.

The front is easy for me, hell, Im holding onto it with the steering wheel, I have a better feel of the front because of that. And with the setup I have on the front I can tell its stiff enough and handling the turns just fine. Its actually very flat, just like I like the front to be.

But the rear needs to be a lil light, or fast for me to get a feel for what its doing.

If I can feel the rear steering then Im a happy camper. But if its trailing and heavy it might as well be a wagon full of hay Im towing through the turns.

No thanks. Guess its odd. But hey, we all have our issues LOL JR

[Dave@Hellwig]

This is the bar we developed for the One Lap Camaro. It is designed to work with a 3 link or 4 link suspension that uses a Watts link. We made it in 1" diameter for the One Lap Camaro, but can also make it in 7/8" or 3/4" diameter. It has 6 hole positions for adjustment and is made from heat treated 4140 chrome moly steel. The 1" diameter version is being released as Hellwig p/n 5867 in January 2011.

[BANKO]

Hey guys, thanks for the responses. I was also looking forward to more of the fundamental suspension design theory on why a sway bar is needed on a 3 Link design? It seems to me that the purpose of a 3 Link + Watts provides the most articulation while keeping both tires in contact with ground. By adding a sway bar, the torsional stiffness of the suspension system is changed, giving it adaptability, but at the expense of articulation. How do you know a baseline for how much torsional rigidity is needed? Got any good books that address these specifics?


@Dave, that is one sweet looking sway bar set up. What diameter axle tube is that mount designed for?


Thanks, Josh

[Dave@Hellwig]

Its designed for a 3" dia axle tube.

[Blake Foster]

Dave that is the same bar we have been talking about for the Speedtech rear torque arm set up is it not? We added the prototype one to my car and it was definatly an improvement!