Proper adjustable endlinks adjustment

[inquirer]

After an unexpected failure (without any particular incident taking place) of my Koni struts sway bar link bracket, I wonder what the proper length of my adjustable end links should be.

The aftermarket sway bar I use is adjustable too and is rated at 72% stiffer than the OE bar for its soft setting and 94% stiffer than the OE for its stiffer mounting position, but at what endlinks length and as a result at what ankle with the bar's arms these rates are valid?

During installation the OE endlinks proved incompatible with the aftermarket sway bar (without altering the original car height). It was impossible to connect them to the bar in order to select the stiffer setting and for the softer setting there was no adequate clearance from the front lower control arm in order for the struts to be able to get fully extended.

To cut a long story short, adjustable endlinks where used in place of the OE ones. They were fitted with the car lifted, but they were adjusted at a length that made the angle of the endlinks perpendicular with the bar's arms when the car was on the ground (and at the same time the arms are parallel to the ground surface).

The OE bar's arms (with the OE endlinks) were not parallel with the ground, but were pointing towards it and of course the endlinks were not perpendicular with the bar's arms (see the following schematic).

And now my 2 questions:

1. Should I adjust the endlinks length in order for them to be perpendicular to the bar's arms or does that increase the bar's stiffness considerably over its intended rate? If not, obviously I will adjust them to a longer length and I will keep a tighter clearance from the lower control arms.
2. Is it crucial for the adjustment to take place with the vehicle on the ground? The opinion I got from an alignment shop is that it does not make any real difference if the car is in the air, because both struts will get equally compressed when the vehicle gets back on the ground and as a result no preload will be added to the bar. According to the shop what makes a crucial difference for the rate of the bar is the length of the endlinks. So does adjusting them on the ground make any real difference?

 

[AZjeff]

1. Adjust then to the length of the endlinks you replaced. Nothing else has changed correct?

2. Most cars don't sit exactly level. After setting one to length put the car on the ground, rock it to find it's "level" place and adjust the other link so there's no preload. Obviously you need a good flat surface to do this on.

 

[inquirer]

1. Adjust then to the length of the endlinks you replaced. Nothing else has changed correct?

2. Most cars don't sit exactly level. After setting one to length put the car on the ground, rock it to find it's "level" place and adjust the other link so there's no preload. Obviously you need a good flat surface to do this on.

1. Nothing else has changed, but as I said the OE links were replaced, because their length was incompatible with the aftermarket FSB.
2. In that case the adjustment on the ground is just a detail, right? We are not talking about a significant preload, because any height difference under normal circumstances would be very small.

 

[AZjeff]

1. Surely an aftermarket AS bar has setup instructions online?
2. If you go to the trouble of having an aftermarket AS bar and adjustable links might as well optimize the performance? There must be a reason you went with the aftermarket bar.

 

[inquirer]

1. Indeed it has instructions: https://www.hardrace-europe.com/med...ia_files/2/0/201742615531215O53F12DD_b310.pdf
   They are completely useless regarding the endlinks. They don't even mention that OE links are incompatible. That was discovered during installation.
2. Of course there is a reason, but how is the reason related with any installation and adjustment instructions?

 

[AZjeff]

Quite a few videos on YouTube about using adjustable endlinks.

 

[inquirer]

Quite a few videos on YouTube about using adjustable endlinks.

Haven't seen any videos addressing the effect of the endlinks' length on the bar's rate.

All of them talk about the same matter: How to eliminate any preload by adjusting the endlinks on the ground.

 

[AZjeff]

Will you be able to feel a difference if you adjust the links to be perpendicular to the A/S bar or if there is an angle other than 90 either way? Maybe someone with specific knowledge about setting up A/S bars will jump in with more specific info about your car, brand of A/S bar, how you use the car etc.

 

[AZjeff]

I meant if you give more details about your car, the A/S bar you have etc.

 

[johnmyster]

Tau equals F times L times sin theta.

Minor changes to end link geometry will only have subtle impact on the relationship between the sway bar bushings and the attachment point to the axle/knuckle/a-arm.

If you want it as stiff as possible, set it up so that the rotation of the bar is maximized per inch/unit of suspension travel.

Ideally the end link is roughly vertical and also roughly perpendicular to the arm of the bar.

 

[AZjeff]

If you want it as stiff as possible, set it up so that the rotation of the bar is maximized per inch/unit of suspension travel.

You have to think about it for a minute but makes sense with what you said.

 

[johnmyster]

You have to think about it for a minute but makes sense with what you said.
View attachment 271770

Assuming the angle of the end link doesn’t then work against you. Because triangles and rotation and stuff. That’s the sin theta term.

Bit in general, probably a good guess.

 

[inquirer]

Will you be able to feel a difference if you adjust the links to be perpendicular to the A/S bar or if there is an angle other than 90 either way? Maybe someone with specific knowledge about setting up A/S bars will jump in with more specific info about your car, brand of A/S bar, how you use the car etc.

I can answer that by experience. For the rear axle I initially had used non adjustable endlinks. The RSB is adjustable too with 2 mounting positions. I then replaced the endlinks with adjustable ones and changed their length about 1.5 cm / 0.6 in compared to the OE. The adjustable endlinks were mounted to the same holes as the non-djustable ones.

There was definitely a change regarding the balance of the car and its tendency to oversteer. The difference was not big, but was definitely real.

Tau equals F times L times sin theta.

Minor changes to end link geometry will only have subtle impact on the relationship between the sway bar bushings and the attachment point to the axle/knuckle/a-arm.

If you want it as stiff as possible, set it up so that the rotation of the bar is maximized per inch/unit of suspension travel.

Ideally the end link is roughly vertical and also roughly perpendicular to the arm of the bar.

Let's say that the blue line represents the bar and the red the endlink. The angle between them is θ (theta).

If F is the force that is applied to the bar when the strut gets compressed then the F1 is the force that causes the bar to deform and apply a force to the opposite side. F1 = F * cosθ

When θ = 0° => F1 = F*1

In other words when the endlink is perpendicular to the bar then the force is maximized.

I'm not sure though in case the endlink is installed with the car in the air if preload can make any substantial difference.

 

[johnmyster]

I can answer that by experience. For the rear axle I initially had used non adjustable endlinks. The RSB is adjustable too with 2 mounting positions. I then replaced the endlinks with adjustable ones and changed their length about 1.5 cm / 0.6 in compared to the OE. The adjustable endlinks were mounted to the same holes as the non-djustable ones.

There was definitely a change regarding the balance of the car and its tendency to oversteer. The difference was not big, but was definitely real.



View attachment 271925


Let's say that the blue line represents the bar and the red the endlink. The angle between them is θ (theta).

If F is the force that is applied to the bar when the strut gets compressed then the F1 is the force that causes the bar to deform and apply a force to the opposite side. F1 = F * cosθ

When θ = 0° => F1 = F*1

In other words when the endlink is perpendicular to the bar then the force is maximized.

I'm not sure though in case the endlink is installed with the car in the air if preload can make any substantial difference.

Yes, when the endlink is perpendicular the torque imparted on the bar is maximized...for a given lever length and given force.

But when you change the geometry you're usually changing all three things - the orientation of the end link, the orientation of the bar end, and the angle between them.

This assumes the endlink is parallel to axle motion and 1:1, and that the effective lengths aren't changing. Kinematics is more involved.