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View Full Version : Thinking about using the C6 rear suspension front and rear.



keithq69
01-25-2012, 01:15 PM
I'm starting on a 69 Camaro in the spring.
I have a C6 rear suspension for the car. I'm going to build a rear subframe to install the suspension in the back with a Dutchman 9" center section.
I was starting to think about how it will work with the front suspension for this season. I am planning on doing the rear this spring, drive the car for the summer and then do the front in the fall.

While I was thinking about the packaging of the front suspension I started to wonder if I could use the C6 rear upper and lower control arms up front as well. I know that up front the pivots would have to be modified for anit dive, the lower should be close to level and the upper should point down towards the rear.
Because of the design of the rear control arms the way the front mount starts at the same distance back as the ball joint I just thought it may make the rack and pinion mounting less of a problem.
The other thing I considered was to swap the control arms from side to side so that the rear mount on the control arm was right at about the center of the wheel. That means there would be no crossmember past that point and the oilpan and exhaust would have lots more room.

I haven't even started to check dimensions yet to see if there would be a benefit I wanted to check here first to see if anyone saw any inherent problems.

Thanks

Keith Quinn.

srh3trinity
01-25-2012, 02:34 PM
I would look at Scott Mock's c6 subframe. He is well known here on the board, and has a great looking subframe for a good price, especially if you have the C6 front component a laying around. I think it uses a fox Mustang rack too. Unless you are a whiz at fabrication and suspension design, it would be hard to beat what he has available.

keithq69
01-25-2012, 05:39 PM
Thanks for the reply.
I wouldn't consider myself a whiz at fabrication but I have built my own subframe in the past.
I have a 3 dimensional suspension rendering program to adjust the geometry.
Just wondering how using the same front and rear would affect the handling.

Keith.

MrQuick
01-25-2012, 11:33 PM
you'll most likely encounter packaging and funky camber gain issues but im curious to see what you come up with.

keithq69
01-26-2012, 04:48 AM
If packaging becomes an issue I won't bother. The only reason I'm considering it is to help packaging.
I don't think camber gain will be an issue. The ratio of control arm lengths and spindle height works well together, the rear suspension has a good camber curve.
My main question I guess is how should the front relate to the rear?
Should the instant centre, camber gain and all the other specs be different?
I know caster, Ackerman and anti dive are front end only issues but what about the rest?

astroracer
01-26-2012, 09:17 AM
I don't understand why you feel re-engineering the rear to work in the front will be better, packaging or otherwise, than what chevy did with their design initially???? I know the offset rear control arm will present steering issues, it was designed for a "no steer" rear suspension... The front suspension is designed around a rack and pinion so what is to be gained? I'm just curious, don't want to raise any hackles. I just find it interesting to hear what other people think about suspension design.
As far as relationships go the "front" should relate to the rear just as it was designed... Changing anything changes everything.
Mark

silver69camaro
01-26-2012, 10:58 AM
Keith,
It took me a couple times reading your post to understand what you are wanting. Doing what you've said would place the control arms in a position to where they couldn't handle lateral loads very well.

In other words, don't do it.

keithq69
01-26-2012, 12:01 PM
You don't know why I would re-engineer something that chevy has designed to work a certain way? Really? Did I just read that?
Isn't this what this entire board and hobby for that matter is all about?
Does any real enthusiast every buy a new Corvette and leave it as built by GM?
Why are you doing what you're doing with your Astro? didn't GM already make all the best choices for you?

You say that you know the offset control arm will present steering issues, how do you know that?
What issues will it present? How will it affect the steering that was designed as a "no steer" suspension as you put it?

Just to be clear, I have a complete rear setup. I've taken some preliminary measurements of the control arms and put the info into my suspension program.
With the uppers and lowers placed with proper pivot points for a front suspension the camber gain is very good, just like it is in the rear.
The front and rear upright is the same from front to rear on the C6, only the hub is different.

I'm not saying that it will work, I'm just trying to figure out if there are reasons up front that it should be dismissed, but I'm looking for the reason it shouldn't be used not just that you know.

Many things have been discovered by trying out something that seemed like it wouldn't work.

Astroracer: I'm not trying to start a flame here with you but I don't think your post offered anything positive.
How about explaining some of your statements with reasons why.
You say "As far as relationships go the "front" should relate to the rear just as it was designed... Changing anything changes everything."
I think we all understand that they need to have a relationship with each other. Many guys here are running modified front suspensions that have no relationship at all to the original front or the current rear suspension in their car.
I realize that the relationship will be changed but what I'm wondering is how should they relate, SVSA, roll center, camber gain. Real data not just that it will change.

Just taking the Stock C6 suspension and throwing it in the car doesn't keep the relationship either, the pivot points need to be modified to allow for the fact that the C6 has a wheelbase of 105.7" and the firts gen F body has a 108" wheelbase. The outside dimensions of a C6 with a 12" rear wheel is 76" to the outside of the tire, the first gen is limited to a touch over 70" so the pivot points need to be moved in to make it fit, this affects the roll center and many other things.

Many things need to be changed in order to make it work properly.

I'm looking for whatever is designed into the pieces that make them poor of good candidates for this not just that you "know" it presents a problem.

Keith.

keithq69
01-26-2012, 12:10 PM
Thanks Matt.

That's the info I was looking for.

Sorry for making my post more complicated than it needed to be.

Just curious, how does moving them to the front change the lateral capability? Is it the fact that they would be swapped from side to side and be seeing load from the opposite side of the control arm that presents the problem?
In other words, its intended to have the front of the arm face the front of the car and facing the back towards the front presents loads on the opposite side to what it was designed?

I hadn't made any decisions to do this was just working with the rear setup and it came to me that it may work up front as well.



Thanks

silver69camaro
01-26-2012, 01:11 PM
Typically a control arm is designed so the "angled" leg (in a plan view) is towards the rear to deal with road forces better. Now if this was the only issue to deal with, you could use the left rear at the left front - however, the ball joint boss angle is at the opposite angle that it needs to be (caster angle is opposite for the rear suspension). Also, the sway bar attachment would be at the rear, which would be a pain.

keithq69
01-26-2012, 02:25 PM
Moving them straight forward would solve the strength problem.
The C6 rear actually doesn't run any caster at all at proper ride height as far as I can tell but does gain negative caster as the suspension compresses.
Where the ball joint taper is in the upper control arm is, there is no angle in relation to the pivot points. With the upper control arm leaning down towards the back of the car and the spindle caster it may have worked.
The lower control arm ball joint boss angle is good if I swap them from side to side and it puts the sway bar mount in the right place.

Okay. looks like it's not worth investigating, that's what I was trying to figure out.

Is there anything to be gained by running the front and rear suspension with the same geometry as far as camber gain and roll centers go?
I know they need to work together but what does that entail?

Thanks

Keith.

Bryce
01-26-2012, 03:41 PM
Keith,

Its always good to think outside the box and start solving problems in a different way.

Here are my opinions. You can read through my thread and understand my background.

Rear suspension needs less camber gain than the front.
The roll centers will affect your roll couple and roll stiffness. There is a balance that needs to be understood.
If you have less roll in the back of the car compared to the front then the added camber gain in the back did not accomplish much.
Ackermann is something rarely discussed here but I think has an impact on the cars performance when pushed to the limits of the tires.
Ackermann is dependent on: lower ball joint position relative to the outer tie rod end, wheelbase and rack placement to front axle line.
Negative Caster will add negative camber to the outside wheel when turning and positive camber to the inside wheel under the same conditions. So how much caster do you need.

I think you understand how things change dynamically so its a balance in compromising all of those things. A stable roll center may give a better handling car than a lot of camber gain.

But I think the most important question will be what is your car used for? AutoX, road race, show, cruising, cool factor?

I think most people on this board are not pushing the car to its ultimate limit, talent and tires are the biggest limitations.

Good luck with your build!

silver69camaro
01-26-2012, 03:59 PM
Keith, you are right on the caster - I goofed. The ball joint pad on the LCA is angle is determined by the SVSA designed into the system. My mistake!

astroracer
01-26-2012, 04:49 PM
If you would have been civil in your response I might not have taken offense. You asked a question why, I outlined some issues and you go off on me for no reason... All you had to do was ask me why. You don't have to belittle me, you don't have to flame my project. I was attempting to start a conversation. That's all.

My responses to your questions are in blue.
Good luck with your project.


You don't know why I would re-engineer something that chevy has designed to work a certain way? Really? Did I just read that?
Yes Sir, you read that right.... A front suspension is a front suspension, a rear suspension is a rear suspension. They were designed to work together. Cobbling up a rear suspension in the front will never work right.
Isn't this what this entire board and hobby for that matter is all about?
What? Cobbling?
Does any real enthusiast every buy a new Corvette and leave it as built by GM?
I don't know and I don't care... I can't afford a new Corvette
Why are you doing what you're doing with your Astro? didn't GM already make all the best choices for you?
If you don't want to "flame me" why are you even going here? I am building the vehicle as I see fit, is there a problem?
You say that you know the offset control arm will present steering issues, how do you know that?
Look at the arms. From the top. Put the suspension in reboumd and try to turn the tire. How far will it go?
What issues will it present?
I guess not being able to steer the car is not an issue...
How will it affect the steering that was designed as a "no steer" suspension as you put it?
The rear suspension is designed around a tire/wheel that does not turn left or right... It goes straight. That is "no steer" as far as I know...

Just to be clear, I have a complete rear setup. I've taken some preliminary measurements of the control arms and put the info into my suspension program.
With the uppers and lowers placed with proper pivot points for a front suspension the camber gain is very good, just like it is in the rear.
The front and rear upright is the same from front to rear on the C6, only the hub is different.

I'm not saying that it will work, I'm just trying to figure out if there are reasons up front that it should be dismissed, but I'm looking for the reason it shouldn't be used not just that you know.

Many things have been discovered by trying out something that seemed like it wouldn't work.

Astroracer: I'm not trying to start a flame here with you but I don't think your post offered anything positive.
How about explaining some of your statements with reasons why.
You say "As far as relationships go the "front" should relate to the rear just as it was designed... Changing anything changes everything."
I think we all understand that they need to have a relationship with each other. Many guys here are running modified front suspensions that have no relationship at all to the original front or the current rear suspension in their car.
I realize that the relationship will be changed but what I'm wondering is how should they relate, SVSA, roll center, camber gain. Real data not just that it will change.

Just taking the Stock C6 suspension and throwing it in the car doesn't keep the relationship either, the pivot points need to be modified to allow for the fact that the C6 has a wheelbase of 105.7" and the firts gen F body has a 108" wheelbase. The outside dimensions of a C6 with a 12" rear wheel is 76" to the outside of the tire, the first gen is limited to a touch over 70" so the pivot points need to be moved in to make it fit, this affects the roll center and many other things.

Many things need to be changed in order to make it work properly.

I'm looking for whatever is designed into the pieces that make them poor of good candidates for this not just that you "know" it presents a problem.

Keith.

keithq69
01-26-2012, 07:18 PM
First of all Astroracer, lets call a truce here.
I'm not trying to start issues I'm trying to resolve them. The reason I answered the way I did was because when I read your reply it seamed like all you were doing was shoot down instead of trying to explain.
Your first question is followed by four question marks, to me that's belittling.
I wasn't flaming your truck, I think your build is great actually and I think the quality of your work is great.
It just seams odd to me that someone who goes so far outside the box with a build as far as vehicle choice and fabrication would question someone for using a part in a way that it's not intended.

As far as the design of the rear suspension arms goes, they are basically a reverse version of what cam on the front of the first gen F body.
The stock control arms start towards the front of the car and lean back towards the balljoint. the balljoint is almost level with the pivot of the rear of the upper arm.
That would be the same configuration as putting the rear arms on the front and swapping them from one side to the other.
For the top view control arm clearance I know what you mean. The one thing that you are not taking into consideration is the fact that the C6 uses a balljoint that is in the upright not the control arm.
that means that during full rebound the control arm is pointing down quite a bit more than it would in a conventional balljoint in control arm setup.
I installed the front wheel on the suspension and raised the upper control arm up over four inches with the wheel at a 35 degree angle and still no contact with the wheel.
At this point the tire would most likely be contacting the frame rail.
So, to answer you. No, not steering the car would not be an issue.

You don't know why I would re-engineer something that chevy has designed to work a certain way? Really? Did I just read that?
Yes Sir, you read that right.... A front suspension is a front suspension, a rear suspension is a rear suspension. They were designed to work together. Cobbling up a rear suspension in the front will never work right.
That's where you're wrong. They are parts and in this case, the strength of the items restricts them from other uses but if they had been strong enough there is no reason why they couldn't be mounted in the front with proper geometry.
With the proper calculations they could be positioned to work very well I'm sure.
The reason I wrote that line is because you have changed everything mechanical about the vehicle you're working with. Saying I'm cobbling it together is insulting to say the least.
What is what you're doing with your vehicle? Is that not cobbling in your use of the word?

I wasn't just going to throw parts at the front of the car, I have a suspension design program. Then I would do what I have done in the past, build a fixture to simulate the pivot points and put the suspension through complete travel and measure the changes. I hardly call that cobbling.

Does any real enthusiast every buy a new Corvette and leave it as built by GM?
I don't know and I don't care... I can't afford a new Corvette
I only brought this up because we were talking about C6 suspension and you questioned why I would change the way GM designed it.

If you had just said to me, the rear control arms won't work because they may hit the wheel under rebound at full lock that would have been productive.

Keith.

keithq69
01-26-2012, 10:27 PM
Hey Bryce.

I read through a bunch of your post, too many pages to get through in one night.
I love the car, you've done a great job on it. Have you had it out to the track at all?
If so, how did it perform?

This will be the first car I have built in a while.
I joined this board the first time when there was only a hand full of members and the post just rolled down the screen, there were no forum headings or anything.
It must be more than 12 years ago. I still see quite a few of the guys that I saw posting back then.
One thing that Larry has back then was a page that had all the members names who submitted pics of their cars, you would click on the name and you could go through all the pics, made it easy to keep track.
There are probably too many members here now to do that.

I would love some advice on what I'm building, when I get some more detailed dimensions and plans I will shoot you a message.

The last car I built before this one was a 69 Camaro also. I did a ZR1 Dana 44 IRS with custom length chromoly dogbones that Katz helped me design for better geometry. The forward link had three holes for each bar to allow for adjustment.
I built my own front subframe using a mix of early and late C4 front control arms and spindles. The geometry worked out really well. Had a good camber curve and basically no bump steer.
I used a right hand drive Saturn rear steer rack that I flipped over and then mounted it in front, the pivot points were perfect and since it was Saturn it worked well with the GM pump.
Kyle at DSE helped me out with that, he had just started Detroit Speed at that time. I started that car in 1998 so it was pretty cool for the time.
The car had an LS1 and T56 and a full chromoly cage. I never finished the car because I ended up getting divorced and had to sell all of the toys.
So now it's time to start something again. I have two young boys, Noah is 13 and Adam is 10. They both love cars and I can't wait to work on the project with them.

As for the use of the car, it will see street use 90% of the time but I do plan on doing some lapping days with the car. I would love to do some autocross if I could find somewhere local to do it.

I need to take better dimensions of the components that I have. My program has a file with a 2001 C5 but I have been told the numbers are not that accurate.
When I get the numbers together I'll send you over the specs for the rear, I'd love to hear your opinion.

Thanks

Keith.

astroracer
01-27-2012, 04:18 AM
Hey, forget it. I am very easy to get along with. The problem with this internet stuff is the lack of tonal inflection in the posts. I meant nothing of harm in my first post and I stated that in the post. I can't control how you "read" it. If you took offense, I'm sorry and we need to get past that and move forward.

The reason I used the term "cobbling" is because the use of the rear suspension in the front is not the intended design use. The rear arms are not designed to carry all of the loads induced into a steerable suspension. The toe link carries a huge amount of lateral load that the upper arm doesn't see when that is in place.
"Cobbling" is not "optimizing", it is getting by with less then desirable parts or materials.
Optimizing is what we try to do with our cars. Not everyone understands the relationships inherent between the front and rear suspensions, you seem to have a good grasp of them which was not mentioned in your first post. A lot of the disconnect here is the lack of MY knowledge of YOUR knowledge. How much do you really know about suspension design? You only have a few posts here so your knowledge,however vast it may be, is unknown to me and the rest of the people on this board.
And, just so you know, Bad Ast is not cobbled. I designed and built both suspensions to optimize the handling characteristics of the those suspension designs and they were built accordingly from the correct materials. No cobbling involved. And Katz helped me also, so we have a common ground here.
I run Performance Trends too so there is more common ground.
Mark