Ah Christ, another engineering project, another edjemakation, jeez, you young punks gotta take it easy on an old hotrodder.... :D

Well so here we go again....Norval...those ball joints look like the way to go, so the question is....does the taper work...will it fit exactly on the vette spindle....there are differant tapers, you know....
second off...the construction looks..well...confusing...hate that term...but I see a long snout, fine..but the flex part of the joint looks sorta like a heim arrangement, more than anything enclosed with booted/captured grease...
ok for race cars...but like my thoughts on steeroids use of them for tie rod ends.....in a daily driven STREET car, out there in the mud and slop....is that a good arrangement.....can/would it last for say years without worry???

also, the fixed extenders are for camaro....any idea what our vettes would need???

GENE

 

I don't know 70 LS1 if adding both would be too much. A line drawn along both upper and lower control arms should fall within the opposite tire , this is th instanteous center. If it is too high the roll center will end up too high. By raising the lower A arm you are raising th roll center.
It is a way of lowering a car though without cutting the springs.

 

First off, Gene Coleman makes some excellent products for race cars. But just because they are made for race cars doesn't mean they are good for street cars. I have used those ball joints on my race car many times but I have also bent and broke them. Unlike a street car the suspension on a race car is dropped out of the car and inspected on a weekly basis to check for damaged parts. An open bearing design like that requires a lot of maintainance. Before I would use them on a street car I would call Gene and ask him his opinion.

What about the Moog Joint I looked at from Speedway? It was an enclosed joint from Moog
http://www.speedwaymotors.com/eCCSto...m/91720032.jpg

Raised pivot joint for raising roll center. Fits most popular racing and passenger car spindles.

#91720032
BALL JOINT UPPER, RAISED PIVOT
(moog ref - K5208 MOOG)
EA $34.95
http://www.speedwaymotors.com

 

A roll center is the imaginary point about which our cars turn

Pete79L82. I knew this wasn't exactly true but I didn't want to get into a long explanation. There is one in the book but I either had to type it out or scan it. Didn't feel like going into it.
You bring up a good point about the open joint. They are open. I am not worried about longevity since I never never drive in the rain, my car is not driven in bad weather and I can always keep an eye that too much junk is not getting in the bearing.
I want to do something in improve my roll center and this seems to be the easiest way to jack it around. Rogers was builds maintains and races 4 cars told me to try it. A 1/2 inch change can make all the difference in the world. He doesn't seem to worry about breaking them on a street machine.
My suspension book is very plain on the fact that sway bars are to come off at 90 degrees. They compared comming off at a angle like pushing a car with a stick at 45 %. Too much side loading.
You obviously know alot more then the rest of us.
Help use try to fix the front end. Teach us about moving this roll center more in line with what we need.
Thank You Pete79L82

 

Norval, Pete, the latest note here by Norval says just 1/2 inch can make a big differance...., well just flipping mounting sided on that controll arm is about 3/8 inch differance, easy...add a 3/8 spacer with BJ on bottom side of controll arm...I would think it should be fine then....might have to angle the spacer to allow for geometry changes presented to the BJ, so as not bind and break them....NO??? I am thinking I can make spacers....

GENE

 

Is anyone using Performance Trends' Suspension Analyzer software program? I just ordered it and should receive it next week. If it is as good as advertised, it might give us some definitive answers as to what dimensions we can modify to achieve the desired improvements in suspension geometry. If we can quantify the geometry changes that need to be made, it would be much easier to fabricate the spindles and control arms necessary to achieve the desired results. Obviously this assumes the software is good and accurate.

Contrary to current claims by vendors and car owners, I am skeptical that the currently available bolt-on suspension components offer the ultimate in suspension and handling performance. I've already got all the bolt on suspension components available, plus alot of custom stuff I have made, but Norval, Chris, and I still feel there's still room for improvement.

 

Prosouth: The K5208 ball joint is the standard joint for 78-86 GM intermidiate (metric frame) cars.(Rear wheel drive Monte Carlo, Grand Prix, Regal, Cutlass) Steal the ones off of your El Camino :rofl: They are longer than the 73-77 Intermidiate and full size ball joint but I dont know how they compare to a Corvette joint. Possibly try a parts house that has Moog and look in the catalog for dimensions. I am about 90% sure that the taper is different from the Corvette joint but Speedway, Coleman, SCP sell ball joint tapered reams so that can be corrected to match.


Norval: Before you should make any changes you have to know where you are at now. Here is some good software to calculate where you are starting from. http://www.performancetrends.com/rc.htm Expect to spend a good day just taking measurments to input in there. Also not every Corvette will be the same as different rate/height springs will change everything.

Gene: Just changing the angle of the a-frame is not what you want. By moving the ball joint from the top to the bottom of the a-frame still leaves the pivot point the same distance from the top ball joint to the bottom ball joint so that will not change roll center at all.


Pete


[Modified by Pete79L82, 9:02 PM 3/7/2003]

 

Anyone have the part #s for the lower ball joints? I really like the idea of adjusting the roll center and lowering the car at the same time.

thanks

 

Pete, of course, you are correct, I just reacted to what I thougt I saw in my mind, and of course it's rong.....yeh, it's the center of the ball stud that needs raising....OK....hummm....wonder what other spindle GM used with taller height that may work without an act of GOD???

I did something similar with my old '70 Lemans/GTO....flipped all sorts of stuff around added disc brakes, and caddy spindles...those old caddy spindles may be an interesting place to start....

GENE

 

Pete79L82. Thank you for the RC calculator. I added it to my favorites for future. The hard part for me will be to measure what I have. The car is off the ground on jack stands and I intend to change the soft front spring I presently have to a set of #460s. This will change the ride height. I took the ball joint out today and will not replace them with the stock ones. My car will come out the end of April with the modified front end.
To do it right I should wait, take all the measurements when it comes out them make the change but I want to work on something now and once it comes out I only want to make changes for testing.
I think I ordered the wrong ball joints but I will start a new post about that.
Thanks for the input.
Have a nice day :)

 

What I haven't heard stated correctly is how the roll center really affects the car. What you are really changing is the distance between the roll center and the center of gravity. The roll center is the point at which lateral loads are transferred to the sprung mass. If the roll center height and the center of gravity height are the same, the car will not roll. Increasing the distance between the two points will increase the lever arm, and increase roll.

About software for suspension, I have two program I will be glad to make copies of and send out. (Don't worry, they are student versions of the commercial versions, and you can download them as well.) One has the ability to do 3D modeling of a complete vehicle for handling, 2D ride analysis, and 3D suspension modeling. The other program will calculate all the suspension information you want based on the geometry you enter. You could use this program to see how the suspension as a whole changes when the roll center is moved, and then re-enter into the 3D model to see how it affects the vehicle. If someone wants these, please email me, and I will burn a CD and mail it to you. The 3D program is very large, and I don't have the bandwidth to email it. If you want to read about these programs, do a search on CarSIM and sSNAP.

Finally, about sway bars; in my previous job I designed sway bars for the OEM's. It is true that a straight bar with 90 deg ends, is easy to calculate, but that doesn't mean they are the only way to go. The bushing and the end links have a huge impact on how responsive the bar is. I would worry about this first. One big problem, is that it's harder to calculate the rate of a curved bar, but it can be done.

Hope some of this helps. Suspension is a very complex subject, and I'm not the expert. I am just trying to pose some questions about and, hopefully ways to investigate, changes to geometry before you spend a lot of time and money. I think it's great that you are doing this. I am doing the same work on my Camaro now, because it needs a lot more help than the Vette.

 

The use of mid-70's Camaro/Firebird spindles is a well known modification to 64-72 A-bodies. The taller spindle does everything you are trying to do on your cars. The drawback is it requires use of shorter aftermarket upper a-arms, or using a ton of shims for alignment. Joe


[Modified by joe73vette, 12:17 PM 3/10/2003]

 

bb69 That is generous of you to offer us the CD.
Pete79L82 steared use to this web site http://www.performancetrends.com/rc.htm
I looked at it and the first thing I thought is I can't take all those dimensions and feed it in.
I just want to try something. I will just replace the spring, the sway bar and add the extended ball joints and see if I like the results better this summer while driving.
I am also worried about too much shimming on the upper ball joint but until I install them and align the car I won't know.

 

Norval,
I would be glad to give you the program, and the Camaro dimensions. This way, you can play with the numbers and see what will happen. Someone else was kind enough to provide the Camaro numbers on another forum. I think you will find it interesting just to play and learn at the same time. The Camaro suspension is basically identical to the Vette in design. They are both unequal length double A-arm setups. Changing the numbers on the Camaro setup will have the same affects as if you were doing the Vette. Many of the guys on the Camaro site use the Performance Trends package, but it's more money than I want to spend. The two programs I mentioned are student versions of very high end commercial programs. Both of these programs have been used at the OEM level. Also, because I got them free in school, I wanted people to know there is an alternative to buying software. It's amazing how many simulation programs are available on the net. Anyway, I applaud you for trying this. That's a lot more than many people will do. Good luck. :cheers:

 

bb69: You are correct in that statement. If the roll center and the center of gravity are at the same height then the car will not roll. The only time this is desireable is on a high banked corner where the car settles "into" the banking instead of rolling over. You want some weight transfer to the outside tire (right tire on a left turn corner, left tire on a right turn corner). The question always is "how much"? On a car with a high center of gravity, soft spring, soft jounce shock on the front corner, soft rebound shock on the rear corner, soft sway bar, hard compound tire, soft side wall tire, or positive offset wheels you will want to raise the roll center. If you have the oppisite of any of the items mentioned you will want to lower the roll center. Plus take into account that the roll center is constantly moving as the suspension cycles and we are again back to the question of "how much"?


Two good example on oppisite ends of the spectrum are Indy cars and Nascar Wisnton Cup cars. Indy Cars have a very low center of gravity, very sticky tires and negative offset wheels and use a much much lower roll center than a Winston Cup car which has just the oppisite. Lokking at an Indy car and you will see that the upper a-frame is almost flat.


If you get the roll center too close to the center of gravity, therefore resisting too much roll the car will enter the corner fine but will get an instant push to it with almost no driver warnimg. This is why the factory will error on having too low of a roll center. This may not be as fast through the corner but will give the driver better feel and feedback in a wider array of situations.


There is a lot of mention of the roll center on a Camaro which will have a much higher center of gravity compared to a Corvette so it will need a much higher roll center. What is right on a Camaro will not be right on a Corvette.


Pete

 

bb69, I sent you a e mail about the cutting a CD with the suspension program. I would like to change the spindle length and see what it does to the roll center.
I also need to try to find my instanteous center because my tie rods should also point to it to prevent bump steer.
Thank you Ken

 

Interesting topic. :lurk:

 

To set bump steer the tie rod assy has to be the samt length (outer tie rod end pivot to inner tie rod end pivot) as the lower a-frame (c/l of inner bushing pivot to c/l of ball joint). Then it also has to be parellel to the line drawn through the lower a-frame pivot points.
On a drag link type steering you then have to move the pittman arm and the idler arm around to get the drag link to stay parallel to the frame as the steering is moved side to side. Generally the drag link will try to move up or down as the steering is moved side to side. Adjustment can be made by either heating and bending the pittman arm or slotting the mounting holes on the idler arm.
Once that is acomplished then you have to get the tie rods to run parallel to the lower a-frame pivots. This can be done by either moving the pittman arm/idler arms evenly or heating and bending the arm that the outer tie rod hooks to.

After all that is done there is a fixture that bolts to hub and is measured with dial indicators as the suspension is moved from 1" below ride height to 1" above ride height. Your freind with the race car may have one of these fixtures you can use. If not I would let you use mine. It is quite large so shipping might be an issue. Let me know.


If you lengthen the spindle and change the demension from the lower ball joint to the arm the tie rod hooks to it will change the bump steer alot. If you lengthen the spindle above the tie rod arm it will only affect the bump steer slightly.

Basically you want the tie rods to be the same length and on the same plane as the lower a-frame so they both run through the same arc.


Pete


[Modified by Pete79L82, 6:38 PM 3/14/2003]

 

Pete, how bad is it considered to be if the tie rods are say 3 inches longer than that lower a arm....centers to centers....?? mine are, and they are lower in the middle than at the ends by about 2 inches....but are very nearly straight across from side view...front/back...everything in line with knuckles...

GENE

 

Gene: That definitley is not the optimum set-up. You have 2 wrongs that may cancel out some of the effects of the other. The longer tie rod assy will give you a larger radius arc but the upward angle will put you higher into the arc.

Without running it through motion my suspision would by that it may be ok on upward suspension movement (above ride height) but would be very bad on downward suspension movement (below ride height).

When checking bump streer on a car you try to obtain less than .010 movement in 2" of suspension travel so it is not something that can be measured with a tape measure. You need to try and find a checking fixture. I think they are too big to ship UPS/Fed-ex but I would have to measure mine up to be sure. Otherwise freight to send it to FL might get pricey. If you know anyone into circle track racing, most good shops have them as all circle track cars have to to checked regularly.

I wonder if anyone that has installed a Steeroid set-up has checked the bump steer on there cars?

Pete