Ball joint- above or below a-arm?
02-01-2017, 12:13 PM
#46
Nordschleife Master
I have to disagree with Bill and others that say that changing the ball joint configuration changes the ride height.
The ride height is set by the strut assembly and the location of the axle in the wheel carrier assembly. The control arm plays no part in ride height.
Ground clearance for the arm, yes. Moving the ball joint up will create less ground clearance for the arm (and increase the effectiveness of factory brake cooling deflectors since it'll protrude further from undercarriage) but not affect the car's ride height.
The ride height is set by the strut assembly and the location of the axle in the wheel carrier assembly. The control arm plays no part in ride height.
Ground clearance for the arm, yes. Moving the ball joint up will create less ground clearance for the arm (and increase the effectiveness of factory brake cooling deflectors since it'll protrude further from undercarriage) but not affect the car's ride height.
02-01-2017, 12:53 PM
#47
OK, so I've been playing at some origami. After folding my sheet of paper and making a arm and then plotting on a set square how much effective length is lost for a given amount of movement it is exactly the same as the a arm I made with a offset ball joint. One voice is correct about the ball joint being flipped on the a arm does nothing more than add clearance under full compression. On my home made graph it didn't affect camber curves or anything else for that matter so I apologise if I have added to the confusion on this issue. I emailed the shop that fitted my suspension and corner weighted the car and he confirmed he had only done it to guarantee clearance to the body. As for moving the ball joint changing rude height this is also (afaik) not true. The best way to think about this is that you are moving the a arm to the other side of the ball joint. The ball joint stays where it is so in reality nothing has changed.
02-01-2017, 03:45 PM
#48
How does moving the ball joint to the top not change where the ball is? There are 2 points that determine the locus for the lower instant center line
point 1 is the ball
point 2 is on the A-arm pivot axis
JMO but all else being equal raising the ball raises the ride height so you are back to where you would have been before lowering the car
the only difference is the virtual arm(which is the arm used to determine the IC's) is now further above the actual arm.
The height of the axle center line is fixed wrt the ball. So once again, How does this not raise the ride height up? The old ditty about connections comes to mind
to paraphrase, the A-arm is connected to the ball, the ball is connected to the wheel carrier, the wheel carrier is connected to the bottom of the shock, the bottom of the shock is connected to the top of the shock thru the spring, the top of the shock is connected to the chassis....
point 1 is the ball
point 2 is on the A-arm pivot axis
JMO but all else being equal raising the ball raises the ride height so you are back to where you would have been before lowering the car
the only difference is the virtual arm(which is the arm used to determine the IC's) is now further above the actual arm.
The height of the axle center line is fixed wrt the ball. So once again, How does this not raise the ride height up? The old ditty about connections comes to mind
to paraphrase, the A-arm is connected to the ball, the ball is connected to the wheel carrier, the wheel carrier is connected to the bottom of the shock, the bottom of the shock is connected to the top of the shock thru the spring, the top of the shock is connected to the chassis....
02-01-2017, 03:49 PM
#49
Ok, as i said from the start I wasn't sure, after further consideration in the light of day, I think that the ball probably stays in the same place and the arm is pushed further down.
But that brings me back to my original problem w/ this.
If the ball is in exactly the same place how has the geometry changed?
The IC line starts at the center of the ball(which is in exactly the same place for under or over) then goes through the A-arm axis(which is also unchanged)
The other line that defines the IC starts it the center of the shock top mount and runs perpendicular to the shock axis.
But that brings me back to my original problem w/ this.
If the ball is in exactly the same place how has the geometry changed?
The IC line starts at the center of the ball(which is in exactly the same place for under or over) then goes through the A-arm axis(which is also unchanged)
The other line that defines the IC starts it the center of the shock top mount and runs perpendicular to the shock axis.
02-01-2017, 03:50 PM
#50
Right, so you're being assumptive in this and haven't measured the curves and geometry.
I'm not going to share info more broadly as to the why, but you can look up my setup there is a reason the engineer set it up that way. He used to support factory 964 and 993 race cars. So a bit more experience than the Internet peanut gallery.
I'm not going to share info more broadly as to the why, but you can look up my setup there is a reason the engineer set it up that way. He used to support factory 964 and 993 race cars. So a bit more experience than the Internet peanut gallery.
If you have an ENGINEER that set up your car believing it made a difference in the geometry, he should turn his degree back in, because he doesn't understand concepts taught in freshmen classes.
02-01-2017, 03:56 PM
#51
Ok, as i said from the start I wasn't sure, after further consideration in the light of day, I think that the ball probably stays in the same place and the arm is pushed further down.
But that brings me back to my original problem w/ this.
If the ball is in exactly the same place how has the geometry changed?
.
But that brings me back to my original problem w/ this.
If the ball is in exactly the same place how has the geometry changed?
.
I can only assume the reason is for clearance, probably done sometime on a severely lowered race car, possibly because there was some other space conflict going on, like brake ducts maybe.
Afterwards, it was copied because someone thought it helped the geometry. Wouldn't be the first time something was copied off a race car for the wrong reason.
Last edited by onevoice; 02-01-2017 at 10:03 PM.
02-02-2017, 05:33 PM
#52
Rennlist Member
I assume gravity is still in effect every day without measuring also, without questioning whether laws of physics have been repealed overnight.
If you have an ENGINEER that set up your car believing it made a difference in the geometry, he should turn his degree back in, because he doesn't understand concepts taught in freshmen classes.
If you have an ENGINEER that set up your car believing it made a difference in the geometry, he should turn his degree back in, because he doesn't understand concepts taught in freshmen classes.
How many race cars have you setup and won Le Mans in?
02-02-2017, 06:54 PM
#53
As someone way too old to know everything---My comment earlier was wrong and onevoice
and others are most certainly correct. The relationship between ball joint and the control arm
and tie rod does not change. And certainly has nothing to do with ride height.
My apologies for commenting without adequate caffine
and others are most certainly correct. The relationship between ball joint and the control arm
and tie rod does not change. And certainly has nothing to do with ride height.
My apologies for commenting without adequate caffine
02-02-2017, 08:11 PM
#54
I wish I was young, i don't know it all, I have set up race cars, (and won) but no, I've never been to LeMans.
02-24-2017, 11:28 AM
#55
Three Wheelin'
Thread Starter
I'm going to poke this horse again for more fun. Let's say you have the new FVD inner tie rods, and you can change the inner pivot closer or further from the wheel carrier. Anyone hazard a guess as to the effect on the toe vs height curve?
I'm assuming that there is enough toe adjustment available on the fvd inners after moving the inner pivot in/out with the steering rack stop. Of course, there is some room to accomplish this with the stock inners too. The spec is a 5mm gap between the steering stop and the fork. I imagine that is only related to changing the inner pivot location.
I'm assuming that there is enough toe adjustment available on the fvd inners after moving the inner pivot in/out with the steering rack stop. Of course, there is some room to accomplish this with the stock inners too. The spec is a 5mm gap between the steering stop and the fork. I imagine that is only related to changing the inner pivot location.
