Pete79L82,
Your points are well taken. What I meant was that changing the geometry on the Camaro will produce the same geometric changes as on the Corvette. Now, what affect that will have on the car is obviously going to be different. However, with any of these suspension programs, you could use the Camaro dimensions and the Vette COG height and overall dimensions to get an IDEA of how changes will affect the car. This would be a way to experiment if you didn't have the Vette geometry. Mainly, I think it's a good idea for someone to see what the changes do to all the other suspension characteristics.

Ken

 

Well gentlemen, it appears that I haven't stayed updated on the CarSIM website. You can only download the animation viewer now. Here is the link for the CarSIM overview.
http://www.trucksim.com/carsim/

I am still willing to make CD's and send them, but if someone had an idea for posting these programs, let me know. For those of you who have already requested them, I made some last night, and the will be hitting the mail very soon.

Also, here is a link to the sSNAP site. This is a consulting firm based here in Michigan. It looks like they have updated the program significantly. The student version I have is not as refined with as many windows, but it does have the 3D viewer.
http://www.suspensionsim.com/suspensionsim/index.htm

Ken

 

Pete. Last summer I spent alot of time trying to get my bump steer under control. I ended up making a pitman arm 1 inch lower then the stock unit and I ended up welding an extension on my drag link to also lower it. My inner tie rods were too high.
I checked bump steer at least 2 inches down and 4 inches up and the change up was inches and almost no change down.
I hope to work on this more this summer. Along with the stronger springs I hope not to move through 4 inches rise on launch.
Thank you for the offer on the pump steer but the shipping would get rediculous and Roger would loan me his.
I too wonder about the Steeroid mounting. If everything is not in alignment toe out is a good possibility. If a line drawn through the out tie rods ends does not pass through the center of the rack toe out happens whenever this becomes a straight line.
Thanks Pete.

 

Norval,
I quickly ran three versions of the Camaro setup so I could see the change to roll center hieght. The results are below in mm.

Stock Camaro is 31.77
Camaro with Gulstrand mod (redrilling a-arm mounting holes) is 81.9
Raising upper ball joint one inch is 86.68

This gives you an idea of what the adjustable ball joint will do. Until we get the Vette geometry, you can use this as a rough estimate.

Ken

 

OK, right now, my tie rods are about 1.25 inches lower in the middle at the rack tie in point, than at the knuckles....now the steeroids takes care of that by raising the attach point above where I have it....
I did not pay any attention to the stock configuration so I can't comment on it...
my measurement of the lower a arm seems to be ~17 inches from BJ center to pivot point center in rear of arm...and my tie rods are 20 and 22 nches long...due to my moving rack toward driver's side in a vain attempt to clear the headers i HAD on the car....wound up changing them anyway....

but thing is here....I think having the tie rods flat level across the car, would make the wheels tow out on the upswing and the downswing....I thought of that, and sort of split the differance.....Jim Shea thought a longer tie rod was a good thing, as the swing arc is reduced, I sorta agree with him...
so my suspension on the downswing, less loading, jounce, will then make the tie rods effective longer, and if going far enough, make them shorter again...
on the bounce, compression upswing...they only get shorter making more tow out....
I would think raising the tie rod centers would help my situation a LOT....
I sorta wonder if I"m not getting way too much tire wear on account of that being too low....
but then again,....Norval, you commented on lowering your stock tie rods/drag link....

so what gives guys????

GENE

 

My center link was too high up in the car. My inner tie rod ends started off higher then the outers so when the car rose on acceleration the inner fixed link rose also and pulled in on the outer tie rods causing the car to toe out worse.By 4 inches of rise the toe had change to a couple of inches.
When I pulled the car down towards the floor and I have the ability to totally collapse the suspension the high inner tie rods moved down and very little change to the toe.
So I reasoned that my inner and outer tie rods should be about the same height. Since my inners were high I had to lower both of them. I did this with a lower pitman arm and extended drag link.
As for mounting the rack I was talking about mounting it in line with the outer tie rods front and back, not up and down.
Mounting the rack behind the center line between the 2 outer tie rods will result in unwanted toe out at a certain degreee of turning.
Mounting the rack 2 inches behind this centerline results in about .500 inches of toe out at a certain turn radius and yet when pointed straight ahead toe is back to normal.
Mounting the rack up and down from this line is another problem.
Some one said a little knowledge is dangerous. I am Dangerous. I have little knowledge. Just enought to get me into trouble.
I am just reading this suspension book and there was a warning about mounting the rack and I am just repeating my interpretation of what they said. Someone else reading it might interpretate something else.

 

Well, the way I look at it, the center of my car being lo, when the car dives at braking, the tires are fored into a toe in...unless it dives over center which is about 1.25 inches....then the go back to normal and then will start to toe out....

so when accelarating, the tires tend to go to a further toe out situation...

but if the tie rods were flat at rest...the tires would allways be forced into a toe out situation regardless of braking OR accelerating....
I looked at that and thought about it a bit....and decided to go with this set up....not entirely sure i'ts correct/best as possible...just that it SEEMED ok compromise to me....

anybody??? Pete???

GENE

 

Gene, you are correct on most of your assumptions as far as where the tires will go. But you are assuming both wheels are doing the same thing so each cancels out the effects of the other. What happens when one wheel hits a rut in the road. Or when you enter a corner hard. On a hard left turn first the nose will drop down, causing a toe in situation, then weight in transfered to the right front tire causing it to drop farther, making the tire start to toe out, all while the left front tire is having weight transfered off of it causing it to rise and go to a toe out situation. This has to make the steering unpredictable as the wheels are not going in the direction the steering is tell them to go, causing a constant correction at the steering wheel.

I see you have larger wheels. Do you have enough room to move the steering arm on the spindle down to get the tie rods closer to the same plane as the lower a-frame? I know there is not much room to move them with 15" wheels but with larger wheels this may be an option.


By using a center take off rack on a car with unequal length a-frame you will never get the bump streer correct. You have to use a end take off rack to do that. But I do think with some work you can get it to an acceptable level.


Pete

 

Ken, I agree. I would rather see the changes made on a computer simulator first and then on a car. Making changes with out knowing exactly what it is doing and what else it can effect can cause some unexpected results. Steering geomerty in not an area to be taken lightly.

I am sure Norval has taken these things into consideration to arrive at the mods he whats to do.


Pete

 

Pete, methinks we need to go offline with this...and second off, methinks real strongly I needs go under the car with some real specific observations written down...IE...NUMBERS.....tmrw I will hopefully have time to drive the car up on ramps, and get under it enough to take actual measurements.....
I tried with a friend down the road, but he is slammed with work....

please send me a email...


mrvette72@interstateweb.net


my largest concern is about anyting being radically rong with what I have done....I don't think so...BUT....a further understanding is allways helpful....

thanks muchly everyone....

GENE

 

mrvette. I am lucky to have a drive on hoist. I spent alot of time lieing on my back on a comfortable rug with the car a few feet in the air and with the aid of a small jack to slowly raise the car and a special hook to slowly pull the car down I could watch what effect the up and down motion was having on the center link, tie rods and spindles and you could just watch the toe change. I just kept looking, jacking the car and finally thought if I moved the center link down it would put everything in a better arc.
I wish I had talked to Pete earlier. He has given me more to think about and of coarse lay under the car and try to visualize what he is telling us. Obviously he knows far more then us.
I can't do any of this now with the car on jack stands but this summer I will get back into looking to eliminate bump steer. It has bugged me for years.

 

Don't go offline now! I'm just starting to get more confused! :lurk:

 

:iagree: If it's not too much of an inconvenience, I would say please don't go offline with this just yet. This conversation is a great way for the rest of us to gain understanding... much better than someone posting some numbers and measurements and saying "this is correct".
The ultimate goal for my vette is to have it as close to a modern car in terms of performance and engineering as possible. The drivetrain is easy to take care of. The brakes are slightly more difficult but still not too hard. The suspension, however, is the most difficult item to remedy. Swapping the suspension from a C4 is much more of a task than dropping in an engine or building brackets for calipers. Naturally there were some engineering compromises made at the beginning that aren't as useful now with the improved tires and larger wheel sizes. Knowing what to change and WHY is an important thing to know for all of us that aren't satisfied with 30-50 year old technology in our cars.
-Jason

 

Gene:

I don't think you have done anything wrong as far as being unsafe. I think we just need to tweak it a little to make it better and get a better feed back to the steering wheel.

Bump steer is the last thing you want to adjust in front end geometry because changeing bump steer will not affect anything else but every thing else you do to the front suspension affects bump steer.

Once you get some measurements let me know.


Pete

 

Pete, I got all 4 about 5 inches off the ground now...and the front wheels are sitting on greased pads and wheels moved around suspension settled in just nicely....really easy to turn the wheel manually, or tires for that matter...

so the looks of it with a string going from tie rod knuckle ends to opposite side is....and this IS strange...shows what trying to site something from not being under the car and definitive get me......

the ceter linkage...rack output is just about an inch low, and two inches to the rear compared to the knuckle position.....the ride height from the bottom of the upper A arm to the frame...there is no rubber snubber...is damn close to two inches...maybe 2.25 inches....

GENE

 

Gene;

Try to get me the following measurements amd be as accurate as you can, to the 1/64" if possible.


The distance from:

The ground to the inner tie rod pivot.
The ground to the outer tie rod pivot
The ground to the inner lower a-frame pivot
The ground to the lowwer ball joint pivot
The length of the lower a-frame from inner pivot to ball joint pivot
The length of the tie rod from inner pivot to outer pivot


I know that some of the demension will be difficult to get accurately but try to get as close as you can.

With those dimensions I can plot the suspension movement out on a CAD program and tell us what you bump steer is with fairly close accuracy.


Pete

 

ttt :lurk:

 

 

Gene: Am I not following this correct? Does this mean that the outer tie rod is lower than the lower ball joint?

Pete


[Modified by Pete79L82, 4:28 PM 3/14/2003]