Adjustable Suspension Geometry

Ive been considering methods of incorporating adjustability into my suspension design on the custom chassis ive been working on and am wondering if anyone can shed some light on the methods i've though of, and tell me if they are good ideas, or shouldnt be tried.

My Goal is to have adjustable, caster, control arm angle front to back for anti-dive.

As most of you know, you can tune out anti-dive in the front by angling the control arms. If you look at a side view of the chassis with control arms drawn, if you tilted the control arms so that lines extended on their planes intersected at the center of gravity, you would have 100% anti-dive at the front, and if you did this at the rear, you would have 100% anti-squat.

Now, this is going to be difficult trying to describe without pictures but ill do my best. this example is assuming you are using spherical rod ends to link the control arms to the chassis. If you tilted the rod ends horizonal, you could put larger or smaller spacers on top or underneath the sperical joint at the front and rear joint of one control arm. Using different sized spacers at the front and bottom would make one end higher than the other, This would tilt the control arm right? And the spherical joints would still be perfectly horizontal. Would this still be effective way of introducing anti-dive technology? or would the spherical joints have to be tilted with the control arm to get the proper arc travel?

My next adjustment goal is caster, in this example you are using spherical joints to attach the control arm to the chassis. The sperical joints are oriented vertically in this example, with spacers in front of and behind the joint. Using larger spacers in front of both sides of the top control arm, and bigger spacers behind both sides of the bottom control arm would place the bottom control arm further forward than the top control arm tuning in some degree of caster right? So could you just use different spacer sizes to adjust the angle of caster you want?

if there is an easier way to go about doing these, please let me know, im just trying to cover my ass so i dont have to be stuck with my original suspension geometry design forever if it turns out to be less than perfect.
 
Clay
In theory what you are thinking is a good idea, but with respect to the upper front arm having spacers on the top and bottom of the spherical joints this would introduce a binding condition unless you elevated one arm and dropped the other (example would be lifting the front upper mount and lowering the rear upper). Always try to have the centerline of the pivots turning around the same pivot point. With respect to your second goal (caster), this is a good idea, and is used on many suspensions (the original GT40 being one), the problem is the time involved in making adjustments, but once done they should never change unless a component becomes bent etc.
I would think that it would be best if you were to use this method to move the front lower forward and the front upper rearward to get the caster you need. Keep in mind that to introduce anti-dive your angle on the upper front wishbone will also angle the outer ball joint with respect to the front upright, and this -depending on your overall suspension travel-may bind the ball joint. Try some cheapo mockups--no need to be pretty here, the real world setup will show immediately if you have any conflicts, and you can take some rough measurements to see the effect any changes to mounts etc. have caused.
Have Fun
Phil
 
What you are saying about rasing the top front, and lowering the top rear is exactly what i was talking about. Using identical sized spacers so that they are each moved the same distance but in opposite directions. So you are essentially rotating the arm.

Since I can only use one of these methods, (spherical joints vertical or spherical joints horizontal), Im going to have to decide if i want adjustable caster or adjustable anti-dive. I would assume caster will be fairly easy to get right the first time. From what i've read, i will want about 5 degrees of caster. The anti-dive seems like it would be more of a pain to dial in, since i dont know what % Anti-dive the car will like, or dislike. But im not sure if i could have enough range of motion for rotation with just using spacers. Is there another way people accomodate for adjustable anti-dive?
 
a friend from another board just pointed this out to me, if i was using the method if putting spacers above and below the rod ends to rotate the axis for anti-dive, the rod ends would be moving closer together as the arm rotated, there for needing the bolts that hold them to move closer too. This seems to be a problem, maybe i will just forget about adjustable anti-dive all together.
 
Hi Clay, i'm having the same problem with my project, i gave up on adjustable antidive.
With the caster i have a top arm that comes from the top outer balljoint at 90 deg to the wheel back to the chassis,just inside the top balljoint attached to the arm the front arm goes forward to form the front part of the a arm, i have used a front top arm from a Renault 25/fuego the joint at the front on the chassis has a nice angle on it and has the arm threaded into it with a very fine thread, if the arm is not long enough i just cut it in two and added a length of tube between.
I have also read that attaching the front upper or lower arm on the centre line of the upper and lowerarm inner mount point horizontally, usually about 1 inch inside each changes the antidive ???? can anyone confirm.

Regards
GraemeS
 
Use something like this, with the inner rod ends turned 90 degrees. (Also aim the front and rear tube axis' at the ball joint center...)

[image]http://www.clubcobra.com/forums/attachment.php?s=&postid=586330[/image]
 
Bob, please forgive me for not understanding at first glance. how would making each side of the control arm indivdually adjustable make it able to tune in anti-dive?
 
The front and rear inner rod ends are turned 90 degrees and vertically spaced as you(?) have described before. The individual links to the ball joint allow caster and camber adjustment by varying their length. Note that the plane of the upper ball joint mounting plate is determined by the front link outer clevis. But - I repeat: The front and rear link axis should point toward the BJ center. This picture shows a flawed design that unnecessarily puts the rear link in bending mode.

uca.jpg
 
so lets say you turned the joints 90 degrees from how they are oriented in that picture, then placed spacers on top of and under the joints, the larger the spacers, the more the arm would rotate, and the closer the joints would get to eachother in the side to side measurement right? So the bolts used to hold the joints would have to get closer together as you rotate right?

imagine a circle, with no angle the rod ends would be at 0degrees and 180 degrees, lets say you put the spacers in, and now the arm is at 5degrees and 185 degrees, the two points will be closer together on the x-axis if the origin is the center of the circle. right?
 
Clay,

You are correct. If you look at the above design, the rear link is welded to the ball joint plate but the front link can pivot at both ends - so the center-to-center distance of the inner rod ends is quite "flexible".
 

Trevor Booth

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Clay
There is no need to have a pivot on the outboard end of the front link (as picture above) if you have rod ends on the inner of both links you shorten one and lengthen the other to adjust caster and shorten or lengthen both an equal amount to adjust camber. To adjust anti dive there is no easy method, you would need to provide a series of holes for pickup points or have the pickup point bracket adjustable in itself. The vertical differential between front and rear pickup points could be in the order of 25-30mm dependant on lots of variables. The suspension design above is not one that I would use, the top pickup points are very close together.
 
Why would the pick-up points for the control arms have to be adjustable. You would just have the spherical joints shown in the picture rotated 90 degrees, and have their mounting area somewhat tall. Then use spacers to move one of the joints up, and the other down. Then having either spherical joints or a hinge at the ball joint would make up for the difference in the x-direction, therefore making it unneccessary to have to move the pick up points, right?

Am i thinking about this incorrectly?
 
Usually the joint may not have enough bump travel as the upper arm typically has ~10 deg slope on it at static ride height. Then you add another 10 degrees in bump and you exceed the maximum of 18 degrees. I guess you could slope up the bolts ~10 degrees to center the joint at the static point.
 
Depending on your wheel travel, angle constraints might be a problem. You should use this type of joint or small-diameter spacers on either side of the joint. This joint allows a total of 76 degrees motion (1/2" - 5/8" size).
3064.JPG
 
Clay, just a short comment. But do we really have use of antidive? In dragracing we use whats called "rise" which is refered to as the same as antisquat. In this case we can plant the tires at the starting line but pay the price later up the strip. Spreading the grip out over a time using the shock absorbers. When talking antidive, this phenomenon is more in use to prevent the car from diving.
As it also affect the braking traction must therfore be taken under concideration.

We could as well be talking "antiroll" as a factor that need to be able to adjust. But here we all know of the drawback in the form of jacking, henche the name "rise" for antisquat.

Goran Malmberg
 
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