An extended spindle in effect shortens the upper A arm creating more negative camber. To picture this pretend the spindle is say 1 foot longer then stock. In order for the ball joint to fit in the upper tapper the A arm would have to be stood staight up and for this to happen the top of the spindle would be really pulled in at the top creating more negative camber.
The extended spindle moves the IC to inside the opposite wheel.
My main concern is creating too much negative camber when the front end rises.
Caster can easily be corrected by milling 1/4 inch slots in the upper cross shafts. 5 minutes per side on a mill is all it takes. I priced replacement cross shafts with the holes moved back and they were $65 CDN per side or $130 for both. My milled cross shafts give 5 degrees positive caster without shims.
My gool too is to remove all or nearly all of the shims.

 

Thanks TT!! That helped alot!!! I had the right points, just the wrong perspective!!

Now, to the problem: Just out of curiosity, if the difference at the ground were slight (under ~ 1" or so) wouldn't slight offset wheels accomplish the same thing? Moving the centerline of the tire inwards with a slight positive offset at the wheel?

I realize this would be no help to someone that wanted to keep the stock wheels, but a custom wheel/custom offset on original?

Thanks again for your help! Between you and Norval, I'm really learning a lot!

Paul

 

I did a little studying last night about anit-dive and the recommendations that somebody made to me are counter to the notion of anti dive. Anti-dive comes when you raise the front of the upper A-arm (or lower the rear of the bottom). I asked the guy again about what he was trying to achieve and all he would say is that it is the hot setup. Not sure how much credibility to give him, but my instincts say it is bad advice.

Chris

 

Here is one solution. The adjustable a-arms are from Pole Position. I relocated the a-arm mounting points to match the cross shaft or you could have the cross shaft made with wider spacing to fit the stock a-arm studs. This enabled me to lower the front mounting point slightly to increase anti-dive.

Also note that I replaced the upper ball-joint with a mono-ball. It uses a much longer stud, with spacers which effectively increases spindle height. All the circle track race car suppliers have mono-***** or if you want to keep a ball joint you can upgrade to a heavier duty Chrysler style screw-in ball joint. Both of these options require the spindle be reamed to match.




(If the photo doesn't show, I've exceeded my bandwith again - be patient, I'll figure it out)

[Modified by 68427, 3:30 PM 1/17/2004]


[Modified by 68427, 3:58 PM 1/17/2004]

 

Also note that I replaced the upper ball-joint with a mono-ball. It uses a much longer stud, with spacers which effectively increases spindle height. All the circle track race car suppliers have mono-*****

68427 I went that route last year and loved the idea but after extensive testing i found they are not suitable for the street. They are made for cars with almost no front end movement. Their range of motion will not permit your car to move through it's full range of travel. Remove the spring and then try the same setup that you have now. 2 things happen, the sway bar linkage goes into total bind if you travel through more then a few inches of travel and secondly and very important is that your mono ball totally bottoms out. The stud hits really hard on one side or the other long before full travel is reached.
At first I thought they were the best and was going to use them with my coilovers but quickly found out they really limit travel and when they bind the stud loading goes way up causing a very potential accident.
I am back to the stock ball joints with their long travel slot.
Trust me 68427 to have really looked into this problem. Mine are sitting on the shelf never to be used again.


[Modified by norvalwilhelm, 3:39 PM 1/17/2004]

 

Anti-dive comes when you raise the front of the upper A-arm (or lower the rear of the bottom).

71roadster isn't this just opposite to anti dive. Our setup places the rear upper a arm stud lower then the front stud so we have kick up?
By raising the rear stud we are introducing more Anti dive? Isn't this what the guy is trying to do by raising the rear stud up 1 inch?

 

Regards those mono-*****: Travel is limited, but I have the 18 degree angled mounting plates which helps. I just checked, it's at full droop right now with shock fully extended and the mono-***** have clearance and it hits the bump stops before binding in compression, so I think I am okay. I am running stiff front coils cut down from a Ford F250 and my car is low, so I don't have room for much travel anyway.

One thing I didn't address is that they will live a short life on a street car. They are not protected from dirt and grit and if you drove it all winter, by spring they would be trash.

Coleman racing products has several upper mono-ball joints that offer adjustable roll center, but none of thier regular ball joints do that.

 

Norval - I am not sure I understand about the sway bar linkage. Mine is nearly stock but I havn't had any binding issues that you mention.

 

Norval - I am not sure I understand about the sway bar linkage. Mine is nearly stock but I havn't had any binding issues that you mention.


The only reason that I went for front coil overs that I could in under 5 minutes pull the spring to check anything in the front end and it can only be done without a spring. If you remove one spring but leave everything else hooked up on that side and go to the other side and remove the sway bar link, come back to the side without a spring and push up on the hub and pull down you will find the linkage goes into very severe bind. My front has 7 inches of total travel and the stock linkage had alot less. The only way I could get full suspension travel is by almost bending the sway bar linkage, Mrvette ran into this too. Most/all people do not check these little things. I do and I find the stock linkage is junk and will run into severe bind long before full travel it reached.
The only cure is heim joint linkage.
I am getting a digital camera tomorrow so I will start to post pictures on these things.
68427 I am forever laying under the car in my shop check/just looking/ trying to understand all movement and relationship between the parts/ checking for free motion/ any play/ anything.
I know my front end/ how it works and I have 7 inches of total free travel.

 

One thing I didn't address is that they will live a short life on a street car. They are not protected from dirt and grit and if you drove it all winter, by spring they would be trash.


This never bothered me. I almost weekly go through the car, it never sees rain or winter driving and those parts are consumable.
If you have stiff front springs most of the things I talk/post about don't apply. I believe in soft springs and long travel suspension/ able to follow the contour of the road so binding is extremely important.
Bump steer is a major problem and must be address.
Putting in cut down F250 basically ties the front end down and makes adjustment useless, nothing moves so how can you have problems with bump steer, binding or anything else??
You just don't have a working suspension. Just one tied down.
I am not trying to start an arguement but I know the problems and if you want the suspension to actually follow the road/ do it's job tying it down with harsh springs is not the answer.

 

Norval, that's precisely the argument that Herb Adams (in the Pontiac Firebird camp) had versus the Camaro suspension guys. That is, IF I recall it correctly! He DID design the original WS6 suspension, so he probably knows what he's talking about!

His argument was to have (slightly)softer springs for better ride, and suspension that would respond to the road faster and better, combined with (slightly) larger sway bars to control the car above the suspension. The Camaro guys went the opposite, stronger springs and smaller swaybars, resulting in a harsher ride. The car had less roll because the springs did the job, but the difference is astounding.

My 2 pennies for the pot!
Paul

 

I have actually increased my front spring rate to 350 pounds from 280 which I really liked. My sway bar is the same as before but with much improved linkage for faster response.
I also raised my roll center with longer spindles to decrease the roll in the corners. The tires will scrub quicker but at the same time the car should respond faster.
Hi roll centers put more input into the tires but respond quicker. Lower roll centers require the car to roll around the roll center before putting input into the tires thus slowing the respons down. Easier on the tire though.

 

anti dive or pro dive (kick up) is only influenced by the virtual wing arm that runs front the hub to the instantanious torque center found when extending the cross shafts.

At that point the brake torque acts on the hub and stries to rotate it. The hub can't rotate but when the suspension bump and rebounces the hub actually makes a rotation and this is what happens due to brake torque. Because the hub wants to rotate the suspension is pushed up or pulled down because of this.

Also the tire load under braking is transmitted into the suspension. Look at the horizontal mvoement of the axis with bump as a ramp. If the ramp is so that it points up (axis moves forward with bump) then it will give anti dive, if the tire moves back (more comfortable) then you have pro dive. The ramp will point down.

If the instantaneous torque center is behind the wheel if will give anti dive when the point is above ground level and pro dive when below, when the IC is in front of the wheels it will give anti dive when under the ground level and pro dive when above it. Just see it as a system of x and y axis with the corresponding 4 quadrants.

So if + = pro dive and - = anti dive:

<- | ->
&nbsp;+&nbsp;&nbsp;&nbsp;&nbsp;-
&nbsp;-&nbsp;&nbsp;&nbsp;&nbsp;+





[Modified by Twin_Turbo, 4:18 PM 1/18/2004]

 

I found some more tho brief description of anti dive and a hint as to why we might want to decrease it (which IS what raising the rear upper A-arm mounting point would do). Herb Adams says you only want 5% - 7 % anti dive in a race car while some production cars have up to 30 percent. One of the reasons he used was that more anti dive increases caster upon compression making it that much harder to turn the wheel. Not sure how much our cars have, but I know how to check.

Also, I have a very good description of anti-dive. The brakes impart a force vector on the front suspension exactly perpendicular to the spindle caster angle. So in my case about 5 degrees above horizontal. This Brake Force vector has two components and can be viewed as the hypoteneus (sp) of a triangle with the base described by the angle of the upper A-arm and the third side described by a force vector perpendicular to the base. The size of the vectors can be determined by the Pythagoreum (sp) H(squared)=A(squared)+b(squared). Where H is the main braking force and A is the main vector and B is the antidive vector.

In our cars, since the caster is less than the angle of the upper A-arm mounting, the smallest force vector points downward and forward and this is the force vector that causes the nose to dip. The main component of the braking force vector points in the angle of the upper A-arm mounts and this is forward and upward which is the force vector which contributes to antidive. None of these force vectors containg any component of the shifting center of gravity which again imparts a downward force on the front end under braking contributing to the downward vector imparted by braking, which combined is more then enough to beat out the antidive force vector and ultimately cause the nose to dip.

I hope that is clear.

And...I checked the angle of the spindle in relation to a line drawn between the center of the ball joints and it is 10 degrees. Which means the king pin angle is 10 degrees. I started reading from the march 2003 issue of RaceCar Engineering and there is an in depth article discussing offset and trail of the steering center. I will try to post more after I decipher it. I would like to get the April 2003 issue as they discuss caster and kingpin angle in that issue.

Have a nice weekend

Chris

 

There's 2 things to anti dive, the brake torque and the movement of the tire contact patch, both related to the mounting of the arms. If the instantaneous torque center is on ground level the result = 0, the higher the more anti dive, the more below ground the more pro dive (this is for a setup with the IC behind the wheels like we have, in front Ã*t's the other way around) so raising the rear arm mount will put the point higher above ground level and INCREASE anti dive. It's really hard for me to explain it in english, gotta find a good desription somehwer. Maybe ther's one on the internet somewhere.

The only thing I can think of is looking at it as a force arm, like a pole vaulter. If you stick your pole in the ground (tire contact patch) then the higher you hold the end of the pole (the end you are grasping) the more leverage you get, if you could (virtually) hold the end below ground you'd be forced down instead of up.. The forward movement of the car and then braking is the same as the speed of a car and then decelerating, the pole vaulters pole decelerates to 0 when he puts it in that little hole. Then the kinetic energy of movement is translated into a forward and up motion.


[Modified by Twin_Turbo, 7:42 AM 1/19/2004]

 

Well, it looks like I missed a little bit of the discussion this weekend. Twin_Turbo, you have said a lot of good things and brought up some good points that I mostly agree with. I wholeheartedly agree that the suspension geometry needs to be completely overhauled. Getting the front roll center in a better location throughout the suspension travel is very important, as is negative camber gain.

I think you covered the potential solutions pretty well. I feel that a combination of relocating the lower ball joint, perhaps a taller spindle and shorter upper a-arms will solve most of the problems. Flipping the upper ball joint will accomplish several things at once. It will make the effective length of the spindle about two inches taller, the angle of the lower a-arm will be more favorable for a lower IC and the angle of the upper a-arm will be changed via the increased height of the spindle. In fact, there may not need to be any more changes to the geometry to fix the IC and RC positions. Of course, if you are going with a clean sheet design then a combination of changing all three is probably better.

I would say that while caster does help with steering stability, it has less effect at small steering angles. However, the camber gain effects of castor angles are beneficial to the suspension. So you want to have a fair amount of caster in the design.

Honestly I don't see the front steer/rear steer argument as a valid one. If there is a bushing compliance steering issue then the bushings need to be switched to something that doesn't deflect. I also think that for a street car, this isn't much of a concern.

The kingpin angle may need to be changed but it is important not to got too far as the steering kickback can get out of hand. The proper way to gain stability is buy designing trail into the suspension. You actually get trail from a greater caster angle. Keep in mind the effects of trail are different from the caster effects although most people combine them when they are talking about caster.

As for anti-dive/kick-up, I don't think we need to get too carried away with this because we are dealing with a fairly high C.G., compliant springs and rough roads. You can't counteract those forces easily with just geometry. I would just advise caution when trying to use this as a panacea type solution. The proper shock valving can do wonders for load transfer in both braking and cornering situations.

 

I see where you are coming from, this is steeroids ;) related. Everyone has their own view on this, I feel that this is a problem. It's not for no reason that most double a arm equipped suspensions nowadays come with front steering end take off racks. Bushings do deflect under load, the only ones that don't are solid bushings and I bet that the people here running solids can be counted on one hand (I have solids w/ teflon liners lying around)

As for changing the kingpin angle, when you change it too much and the scrub radius decreases you will loose steering feell/feedback, not a good thing at all.

Another thing, in my search for spindles I may have found something for myself (brake issues related) but I need the spindle snout profile. Does anyone have the measurements on this and how different is a camaro snout for instance, does it accept our hub (I don't have a 2nd gen camaro spindle so I can't check it)


[Modified by Twin_Turbo, 10:58 AM 1/19/2004]

 

I am bothered by the shorter upper A arm. Our arms are already short enough and when combined with a spindle just 1 1/2 inches longer then stock it quickly goes into negative camber and can quickly jump to negative 3 degrees and that is getting a little much.
I have the time and ability to quickly make a set of tubular upper A arms but it bothers me that I would be doing away with the stop. When jacking the car the wheels would really hang down, when until the shock bottomed out at least. I don't know if this bothers a shock or not but it bothers me.


With too much time on my hands I am thinking about making a brake rotor balancer. Those rotors weigh enough and I would like to balance my 4.
Got a digital camera this weekend and after a little practice I can start posting new pictures. :) :)

 

Mr. NorvalWilhelm, please let us know (maybe in a separate post?) what you find when attempting to balance the rotors. Do you anticipate that they'll be out-of-balance enough to impact the balance of the wheel-tire-rotor-hub assembly?

 

OK - I'm already distracted enough, so my brake rotors will wait to be balanced.

I'm very pleased that you now have a camera. I was getting ready to do a forum
fund raiser to get you one.

Look for my posts coming up on the frame gussets/repairs. I'm getting close to painting (I hope).