Adjustable strut rods - durability for street use

360notch said
I imagine this will start a holy war, but my preference is adjustable struts (like Firm Feel) without heim joints, and rubber strut bushings. I have tried to be open minded about the benefit of heim joint struts, but have not gotten a good technical response from any of technical people I've talked to at 4 companies that sell them. So maybe somebody here can clear this up for me. The heim joint length makes the effective strut radius to the LCA shorter than stock, because the strut now rotates from the heim joint rather than from the K-member. As the LCA goes up and down, the struts push/pull sideways on the bottom of the LCAs because the distance from the bottom of the LCA to the heim joint changes, and the strut is a fixed length, aside from strut bushing give. The shorter the strut radius, the farther will be the sideways push/pull per vertcal distance of LCA movement. The original equipment, softer strut bushings allow some compliance to reduce that movement, but the stiffer bushings don't have much give. So, more push/pull from shorter strut radius, plus less bushing give, impedes LCA vertical freedom of movement and increases the amount of movement at the bottom of the LCA. Stiffer strut bushings probably give better steering wheel control when going over potholes and bumps than do the original factory bushing, but that could be achieved by stiffer strut bushings alone, without the heim joints.

Separate issue, heim joint struts and stiff bushings are wrong for drag racing, because they will hinder the unsprung weight from falling at launch.

You've got your theory correct, the shorter strut rod would create a shorter arc that can put more push/pull force on the LCA as it travels up and down.

If the strut rod was perpendicular the the LCA, that would have more of an impact. Since they're at an angle and both the strut rod and LCA travel in arcs, there is overlap. In that overlap there isn't any detectable binding.

The reality of it is that in the range of suspension travel that these cars have, ~5.5" total, the shorter strut rod does not induce noticeable binding if you tune the length correctly to the middle of the range of travel (which should also be your ride height, you can adjust the height and match the travel by altering the heights of the bump stops). I have set up several cars with the adjustable strut rods, I've had no issue getting the full range of travel to be free without binding. If you take out the bump stops and allow more travel, you can start to feel binding at the extreme ends of the range. But that's with more travel than should be allowed.

Stiffer bushings at the strut rod are a trade off. They do resist more fore/aft movement of the LCA, which is good because it reduces caster change. That kind of travel is in the video I linked above. The problem is that the stiffer bushing there will also add more resistance to the up and down suspension travel of the LCA, which you do not want. You want the LCA to move as freely as possible, so the suspension reactions aren't altered by stored energy unloading.