Function of adjustable anti-roll bars

I have mounted �hlins road and track on my 996 c2, so it is a bit lower than normal. I am thinking about the anti roll bars. What is the correct length of the drop links? I have seen that they sell for normal ride hight and for lowered cars (sport chassis) and also adjustable drop links. What is the difference in ride experience? And what do you actually adjust with adjustable anti roll bars? The anti roll bars are unloaded when the wheels are in the air, so what do you physically change when you adjust them? Robert

The difference is that when the car is lowered, the set length/stock drop links will (pre) load the sway/anti-roll bars - this is un-desireable. adjustable links allow you to adjust out the (pre) load.

Adjustable anti roll bars allow for changing the roll stiffness of whichever end you mess with. It allows for balancing the car to, typically reduce understeer. If you don't know what you're doing, or why, it would probably be best to start at the softest setting. Softest will be with the links as far from the bar's line of rotation as possible.

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This is true if the drop-links have adjustable length. I may have misinterpreted the question. You typically do not want any load (no twist) on the anti-roll bars when the vehicle is in static position. This means on the ground and with typical operational weight (driver, passenger?, fuel, etc.).

But I thought the sway bars only connect the two wheels together. How is it possible to get load on the sway bar when stationary and the wheels are level on the ground?

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There is a lot more to it than "connecting" the two wheels. Under most conditions there should be no load on the anti-roll bar. But things are not always as they should be. On most vehicles there is a limited amount of space for the anti-roll bar and the drop links to exist within their allotted space and function with the rest of the suspension. This is the reason some drop links have length adjustability. If you have suspension that has adjustable ride height (e.g. coil-overs), you will want to adjust the drop link length to properly locate the anti-roll bar. If the links are too long, you will force the ends of the bar downward. Alternatively, if the links are too short they will pull the bar upward. Neither condition is ideal for the function of the bar. Worse still, if the ends of the bar are not located within their normal space, there can be interference between suspension components. This can lead to very unusual handling characteristics or even premature part failure. Taken to an extreme, it's possible to have preload in the anti-roll bar if one drop link is adjusted to a different length than the other. There are a number of other possible scenarios whereby preload can exist in the bar. Accident damage, worn bushings, etc. are a some examples. In other words, it is possible to have load in the bar when stationary and on level ground. Is it likely? Not really, if there is no excessive wear or damage. However, you still need to locate the ends of the bar if you have adjustable suspension. Altering roll stiffness with adjustable anti-roll bars is a whole other chapter, for another day. From the authority on all things about anything... https://en.wikipedia.org/wiki/Anti-roll_bar The first photo in that article in interesting.

Great description Scott! and good article. I also envision that the angle the sway bar meets the drop link, would also make a difference, no? I'm visualizing holding a wrench on a bolt, with the wrench in, say the 2 o'clock position (or 4 o'clock), will require more vertical force (if pushing straight down, perpendicular to horizon), than if the same wrench was at 3 o'clock. The position of the adjusting holes in the bar are effectively a longer or shorter wrench, no?

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J - you're mixing two components of this equation. 1) You are correct, there is a small influence due to the angle the drop link makes with respect to the bar. Ideally, the link should always be vertical and the bar (lever arm) should be at a 90 degree angle to it. We know this can't be accomplished at all times through the full articulation of the suspension. To reduce the inefficiencies of this, the drop links usually have ball joints at each end. There are many designs where rubber bushings are used to compensate for the change in angle of the drop link. This is usually on inexpensive passenger cars, as opposed to sportcars where handling is a big selling point. Compare the "droplink" on one of my little race cars against the 911 design. The 944, actually uses rubber bushings as well. 2) The adjusting holes in the bar are for an entirely different purpose. This is most accurately referred to as an adjustable anti-roll bar. The adjustability is to change roll stiffness. The idea is to tune the balance of the car when in a turn. Most cars are designed to understeer. The way to tune this, is to either reduce front roll stiffness or increase rear roll stiffness (or both). This is typically accomplished by either increasing the diameter of the anti-roll bar, so it takes more effort to get it to twist (torsion), or by shortening the lever arm (or both). My Audi A4 understeered like a pig until I put an adjustable anti-roll bar on the rear. Not only is it a larger diameter bar, but it also has two adjustment holes on each end. I messed with a couple of settings and decided it was best at the full stiff setting (the shortest lever arms of the bar). Think of a torque wrench. If you have a one foot long wrench, it is more difficult to achieve the desired torque than using a two-foot long wrench. The point is, the shorter the lever arm, the harder it is to achieve the same amount of torsion (less body roll). Here's a photo of the rear bar on my Audi. You can see the link is in the rearward adjusting hole, thus introducing the most available roll stiffness (shortest lever arm).

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Different struts/shocks also have different mounting points which will change the length needed for the drop links - not all adjustable links will fit the bill (ask me how I know...). Generally speaking, for an adjustable link, you should measure the static length needed (under load) and then get a link that fits that length within it's adjust-ability parameters (not all the way open or all the way closed - toward the closed end of adjustment is probably best/strongest). Good luck

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I pretty sure I understand, I just didn�t articulate it very well . I understand the drop link ball, and the need to move (ball joint), I was just trying (poorly) to use an image to convey the thought. I was suggesting that, for ideal setup, the relationship from the sway bar (anti-roll bar) to the drop link should be 90 degrees in static position. This is all assuming that the link position is the same on the shock/carrier and there is no fouling with other suspension components. And as far as the holes go, that was exactly my point, the holes farthest from the transverse portion of the bar provide the greatest leverage, therefore make for the softest setup (easiest to turn the wrench). At the end of the day, it�s all about levers was my point.

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I left off an important qualifier: " I think , you are mixing two components". It's all good. Hopefully my explanation will help others. Suspension systems are rather complex. The more adjustability there is, the more complex they become. Yes, levers and torsion bars. Even springs are torsion bars at the 'micro' level.

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^^Ha! No, actually - I misinterpreted the question - which was about adjustable sway/anti-roll bars - not drop links... It's funny how our minds work (or don't work) sometimes...

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I'm not so sure. You picked-up on the question the OP had regarding the proper length of the drop links. I picked-up on the question in the thread title. Who's right? I kind of got all big-winded and tried to answer both questions... Maybe the OP can better explain what he is looking for.

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Yup. Coil springs are another thing that is often misunderstood. We haven�t even touched high speed and low speed compression and rebound adjusters and the effect of spring rates, let alone rack, Ackerman, scrub, etc, etc. I remember tuning MX suspension back years ago, and one of the factory Ohlins techs telling me he wished the factory would just weld the adjustments in place, so people couldn�t f*&* them up so badly

Following up on the bit about drop links. If I�m considering lowering my car slightly (e.g. H&R springs) do I need to also install adjustable drop links, or can I keep the stock ones?

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I�ve had no issues with H&R lowering springs on B8s. The angle, drop link to anti-roll bar is not exactly 90 degrees, but no contact on any suspension components.

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Thank you, I got answers to the questions I had. I am thinking about replacing the droplinks in the front since I think one is shot. So I needed some info about what to look for.

My apologies for the highjack too robo_porsche. Glad you’re sorted.