Strut Rod Discussion
12-10-2007, 09:57 PM
#11
6th Gear Member
Join Date: Apr 2007
Location: California
Posts: 10,468
RE: Strut Rod Discussion
ORIGINAL: Deviousfred
well, if you think about it since the strut rod mounting point and the LCA mounting point are in-line and both mounting locations lie on the same plane, as the ball joint travels around the axis of rotation the strut rod will not try to change lengths. take an acrylic 30/60/90trianlge. Pretend the 90 degree corner is the LCA mounting location, the 30 degree corner is the strut rod mount location, and the 60 degree corner is the strut rod/LCA meeting point. The side oppostie to the 60 degree angle is our axis of rotation. if you rotate the triangle around this axis the strut rod stays in constant contact with the LCA. You have to remember because of the strut rod mounting design it not only has the ability to move up and down but also every other direction although movement is somewhat limited.
ORIGINAL: 67mustang302
Even if the strut rod is in line with the LCA pivot point, you have to account for the fact that the strut rod isn't in the same horizontal plane as the mointing points parallel to the ground. The strut rod is angled downward, so there's always going to be some forward/backward movement of the LCA during suspension travel, but yeah, it's so minor that you'll never notice it. Theheim joint setups are nice, but they're primarily to allow for more positive location of the LCA and allow for free movement. The entire job of the strut rod is simply to locate the LCA front/back relative to the chassis, and the LCA pivot pointand the strut rods are bushed to allow for movement. With soft bushings that can be a problem, since they allow so much movement that LCA deflection occurs because the strut rod is not able to positively locate the LCA, with harder bushings, such as poly you get much more positive location of the LCA, but there's less ability to deflect, which can lead to a stiffer ride. The advantage of the heim joints is that they have no play like a bushing so you get positive control arm locating, yet they havea very wide range of motion, so full suspension articulation can occur.
Basically, don't wast you're time making a whole new bracket yadda yadda. If you could measure it on an alignment rack, I doubt the difference in caster change from LCA movement rearward on suspension compression would be more than a couple tenths of a degree between mouting the strut rod at the factory point, or where the aftermarket kits mount. Besides, that's why you adjust caster anyway, so that on corning with suspension compression you have the proper amount of camber in the tire(if you're running positive caster, which you should if you want good steering control and cornering).
Remember, that strut rod is also angled downwards as well, and as the suspension travels through it's range the change in angle of the strut rod relative to the ground/chassis will have a minor effect on caster, moving the LCA forwards or backwards, but not enough for you to feel. Making up a whole new bracket isn't going to change that, and the effect of a slightly different mounting location will be definately not worth the time involved.
Even if the strut rod is in line with the LCA pivot point, you have to account for the fact that the strut rod isn't in the same horizontal plane as the mointing points parallel to the ground. The strut rod is angled downward, so there's always going to be some forward/backward movement of the LCA during suspension travel, but yeah, it's so minor that you'll never notice it. Theheim joint setups are nice, but they're primarily to allow for more positive location of the LCA and allow for free movement. The entire job of the strut rod is simply to locate the LCA front/back relative to the chassis, and the LCA pivot pointand the strut rods are bushed to allow for movement. With soft bushings that can be a problem, since they allow so much movement that LCA deflection occurs because the strut rod is not able to positively locate the LCA, with harder bushings, such as poly you get much more positive location of the LCA, but there's less ability to deflect, which can lead to a stiffer ride. The advantage of the heim joints is that they have no play like a bushing so you get positive control arm locating, yet they havea very wide range of motion, so full suspension articulation can occur.
Basically, don't wast you're time making a whole new bracket yadda yadda. If you could measure it on an alignment rack, I doubt the difference in caster change from LCA movement rearward on suspension compression would be more than a couple tenths of a degree between mouting the strut rod at the factory point, or where the aftermarket kits mount. Besides, that's why you adjust caster anyway, so that on corning with suspension compression you have the proper amount of camber in the tire(if you're running positive caster, which you should if you want good steering control and cornering).
Remember, that strut rod is also angled downwards as well, and as the suspension travels through it's range the change in angle of the strut rod relative to the ground/chassis will have a minor effect on caster, moving the LCA forwards or backwards, but not enough for you to feel. Making up a whole new bracket isn't going to change that, and the effect of a slightly different mounting location will be definately not worth the time involved.
Dude, you didn't listen to me.THE STRUT ROD IS ALSO ANGLED DOWNWARDS!!! Look under the car, the strut rod is not in the same plane as the strut rod and LCA mounting locations are. You're visualizing a 2D configuration, when it's a 3D configuration. As the strut rod moves with the LCA, it's mounting point at the LCA stays constant, but the rod is pivoting from the point at the chassis, which means that the strut rod is traveling in an arc as the suspension articulates up and down. As the suspension is compressed and the LCA moves upwards towards the chassis, the strut rod does as well, but it swinging in an arc, causing the strut rod's mounting location on the LCA to move upwards with the LCAAND towards the rear of the car. That means that the LCA is moving back and forth as it moves up and down. It's similar to how a 4 link operates, using the angle of the link to change how the axle housing moves forwards and backwards relative to the car.
If anything, shortening the strut rod will result in more forward/rearward deflection of the LCA relative to the chassis.
12-10-2007, 10:16 PM
#12
3rd Gear Member
Thread Starter
Join Date: Jul 2005
Location: El Paso, TX
Posts: 630
RE: Strut Rod Discussion
I heard you the first time. I know the rod is mounted at a downward angle in comparison to the strut mount/LCA mount horizontal plane. And believe me I am not looking at this in 2-D. You are right in saying that the strut rod travels in an arc, but in fact it travels in more than just one arc. IT travels up and down on a z-axis, AND it also travels left and right on the xy-plane. IF xyz isn't 3-D then I don't know what it. So then you must take every intersection between each arc and what you will end up with is the path of the strut rod/lca meeting point. You have to keep in mind the lca does not travels in a straight up and down line but rather in a circle around the lca mounting location.
this is why a protractor will always draw a circle when rotated around an axis perpendicular to the paper.
this is why a protractor will always draw a circle when rotated around an axis perpendicular to the paper.
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