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  #11  
Old 01-05-2015, 09:36 PM
Bfit Bfit is offline
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Looking at the PDF attached above
I think you will find the base c3 weights about 2000 lb on the front and 1400 lb on the rear . Roughly
Bfit

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But I think you have just put up an example to show how you can work this out

I do like the idea of using a suspension analyser to work out how the geometry will function . A lot less guess work and you will get an idea of camber gain etc to get some performance out of your suspension

Last edited by Bfit; 01-05-2015 at 09:40 PM..
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Old 01-05-2015, 10:51 PM
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vette427sbc vette427sbc is offline
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Originally Posted by Bfit View Post
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I do like the idea of using a suspension analyser to work out how the geometry will function . A lot less guess work and you will get an idea of camber gain etc to get some performance out of your suspension
Having never done this or any other major suspension design before, Im excited to try it out. Messing around with the stock C5 pick-up points the analyzer shows that just narrowing it ~3", the geometry turns to sh!t. Im hoping to get both the front and rear optimized to work with the vehicle as best as I can
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  #13  
Old 01-06-2015, 01:19 AM
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mrvette mrvette is offline
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WAY in hell over my head guys, I stick to my 'tronics', 'lectrics'.......

you know, something DOO able.....
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  #14  
Old 01-07-2015, 05:18 PM
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mfain mfain is offline
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Originally Posted by Bfit View Post
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I do like the idea of using a suspension analyser to work out how the geometry will function . A lot less guess work and you will get an idea of camber gain etc to get some performance out of your suspension
Having never done this or any other major suspension design before, Im excited to try it out. Messing around with the stock C5 pick-up points the analyzer shows that just narrowing it ~3", the geometry turns to sh!t. Im hoping to get both the front and rear optimized to work with the vehicle as best as I can
Having been down the path you are now on, I highly recommend you check out the following link: [Only registered and activated users can see links. Click Here To Register...] Ron Sutton is a genius when it comes to suspension design and he puts the concepts into very simple explanations. A couple things you should note about the C5 suspension is that, unlike old school thinking, the upper and lower control arms angle up (the UCA only slightly) toward the center of the car, producing a very long lateral instant center (swing arm) that actually limits excessive camber gain with travel. The second is that the lower control arm inner pick-up points are angled up toward the rear of the car. This helps produce caster gain with travel, which then translates into "good" camber gain when the wheels are turned. You are correct in noting that, as you narrow the suspension, the geometry changes. I ran into the same thing as I built longer control arms, and the geometry correction involved re-computing the heights of the pick-up points of the control arms to re-establish an acceptable instant center and roll center. I found it useful to do full-scale drawings starting with the roll center height I wanted to achieve at full suspension travel (the suspension height you anticipate during braking and cornering - mine is a high travel set-up limited by shock bump stops), then putting the data into Performance Trends to verify. Good luck with your project.

The following is in the "for what its worth" category and is how I approach defining the suspension pick-up points in a generic sense. It sounds complicated, but following your suspension program, it's not that bad. First, you have a few "hard" points already defined based on the spindle and tire width/backspacing you have chosen. Those are the wheel mounting flange height and depth, the lower ball joint center, and (subject to minor variation for camber adjustment), the upper ball joint center. Remember that the C5 suspension is designed for a deep backspace wheel to reduce scrub radius, so you will have to factor in things like wheel-well and fender lip clearance (especially at full compression) when you select your wheel. You need to be able to turn the wheel 27-30 degrees at full compression and roll. Do what you can to minimize scrub radius, but in the end, dynamic caster becomes more important. You know the C5 kingpin inclination angle (KPI), and your dynamic (at compressed height) caster should be 1.5 to 2 degrees greater than KPI for optimum cornering. The caster angle, the vertical location of the wheel centerline with respect to the centers of the upper and lower ball joints, and the fore-aft wheel centerline define the actual locations of the ball joints (the outer pivot points of the control arms). I enter the ball joint centers into the suspension program assuming compressed suspension height (i.e., with total caster at 1.5-2 degrees greater than KPI and initial camber at what I desire for pre-turn-in conditions. Remember, you will gain camber as the wheels are turned due to the caster. Then I would set my roll center at the height I want for a compressed suspension (1-2 inches -- less for road race, more for autocross). Roll center at ride height really doesn't mean much, it is the dynamic roll center that affects how the car handles. Draw a line from the center of the tire contact patch, through the roll center, inboard to a distance, let's say the same as the C5 (which is very long - 250 to 300 inches, or so). The inboard end of this line defines the lateral instant center point. Then draw a line from the upper ball joint center to the same instant center point. The control arm centerline inner pivot points fall on the two lines that run from the ball joints to the instant center at the appropriate control arm length. Realizing that you have defined the control arm pivots at their centerline, you still need to define the vertical location of each end of each control arm (front and rear). For these, I would start with the C5 relationships - upper control arm angled slightly down in the rear, lower control arm angled up in the rear. These angles define your anti-dive and the rate of caster gain during suspension travel. Raise the figure to ride height, and you can then see the control arm pick-up locations for fabrication. I actually build mock-up control arms out of scrap tubing and cheap ball joints so I can run the suspension through its travel and verify caster gain and the effects on camber at various turn angles. I also make all of my pick-up points adjustable so I can make minor tweaks later on if necessary. Hope this wasn't too confusing.

Pappy
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Last edited by mfain; 01-07-2015 at 07:54 PM.. Reason: Additional thoughts
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  #15  
Old 01-08-2015, 04:10 AM
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vette427sbc vette427sbc is offline
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Hey Pappy- Were on the same page, just different forums
Ive been submerging myself in Ron's posts over on pro-touring for the past few weeks. I was actually hoping for your input on the C4 rear geometry as I see you run a similar setup.
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Old 01-08-2015, 06:52 AM
Bfit Bfit is offline
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Pappy hello
Read your post. And just making things clear .
Bottom are in C5 IRS pivots upwards to the rear how ever the connection point angle upwards to the front.
I believe that is what you are saying in your post.

The bottom are at the connection points is a 9.5 degrees up from rear to front the
Top arm is 0.5 degrees down from rear to front and
0.3 degrees a side angle inwards from rear to front ( I'll have to check that as working of memory that may be overall angle )

My measurements are off one car only and there will be variations do to production tolerances
And these numbers are for standard width track.

I am interested to see where this thread goes
As I have a C4 IRS that I'm playing with at the moment as well as researching C5 suspension

The more players the more info we all get

It is posible to fit the c4 or C5 IRS. To a c3 at its standard width for the respective C4/5 IRS if you go to flares and use the c4/5 ofset rims

A C3 looks quite nice with 2" custom image flares and 12" rims under the rear
Hence I'm working on fitting standard width C4 to this C3 and C4 front suspension.
Bfit

Last edited by Bfit; 01-08-2015 at 07:17 AM..
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  #17  
Old 01-08-2015, 05:08 PM
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mfain mfain is offline
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Quote:
Originally Posted by vette427sbc View Post
Hey Pappy- Were on the same page, just different forums
Ive been submerging myself in Ron's posts over on pro-touring for the past few weeks. I was actually hoping for your input on the C4 rear geometry as I see you run a similar setup.
I spent some time with Ron at the Goodguy's finals in Scottsdale, and we discussed rear suspensions in detail. He is and has always been a "straight axle" advocate and his race cars are based on a disassociated, offset three-link, but after watching Mary Pozzi's Camaro with the Art Morrison IRS at the Goodguys, he conceded the obvious benefits. Here are my thoughts on the C-4 IRS. You can generate the same suspension geometry (roll center, camber gain, degree of roll steer, etc.) with the C-4 set-up as you can with the C5 control arm set-up. The difference is that you have to deal with the axle shaft that is a loaded suspension member, but not really a big deal unless you break it. Four areas that can and should be adjusted to suit your particular application are: 1) length of the forward links. Longer is better as it slows down suspension geometry changes, but room is limited with a C-3 frame. 2) angles of the forward links to establish the instant center and anti-squat. I make the forward pick-up points adjustable much like a standard drag-race four link. 3) The length of the toe control rod. The C-4 uses a long link here which introduces some roll steer that "tightens" the car with roll to keep some bozo from backing it into the outside wall on an on ramp. Notice that the C5 and later shortened the rod to eliminate some of the roll steer. You can treat the toe control rod the same as you would the front tie rod when you establish the mounting points which allows you to control or eliminate "bump steer". and 4) the inboard end of lower strut rod needs to be adjustable vertically so you can adjust the roll center. This adjustment also changes camber gain, but in a high travel, low roll set-up the rear suspension does not travel much (a couple of inches), so roll center is more important than camber gain.

Track width is easy to adjust by changing axle shaft and lower strut rod length. Stock C-4 axle shafts can be shortened fairly inexpensively. I used custom built shafts from the Driveshaft Shop to handle some fairly heavy torque loads. You can run a fairly deep backspace wheel (7 inches +) with the C-4 upright without interfering with the forward links. I use a 13 inch wide wheel with 7 inches of backspace, and I widened my rear fenders to accept a 345 rear tire. One other note - if you shorten the half shafts too much, you get some fairly undesirable geometry changes with travel. In this case, it would be better to go with the C5 set-up where you can keep the suspension links (control arms) a little longer and accept a short axle (on CV joints) that is not acting as a suspension link. We did this on my brother's Jag 120 with C-6 suspension. The rear suspension was narrowed 13 inches!

Hope this helps. I've attached one photo of the Jag's narrowed suspension, and I'll put together some other photos to show some of what we have discusses.

[Only registered and activated users can see links. Click Here To Register...]

Pappy
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  #18  
Old 01-08-2015, 05:15 PM
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SuperBuickGuy SuperBuickGuy is offline
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The criticism I've heard - and I could blame for an issue I have/had with my car is this:

Since the driveshaft is a loaded member, on hard corners the force spreads the carrier thus reducing the ability of the clutches to keep both tires spinning.

true? false? but given what you've said - would you achieve the same benefit as a C4 suspension by simply putting an upper bar and removing the c-clip?

please excuse the sentence construction, it's probably as stuffed up as my head...
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Old 01-08-2015, 05:38 PM
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mfain mfain is offline
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Originally Posted by SuperBuickGuy View Post
The criticism I've heard - and I could blame for an issue I have/had with my car is this:

Since the driveshaft is a loaded member, on hard corners the force spreads the carrier thus reducing the ability of the clutches to keep both tires spinning.

true? false? but given what you've said - would you achieve the same benefit as a C4 suspension by simply putting an upper bar and removing the c-clip?

please excuse the sentence construction, it's probably as stuffed up as my head...
I have not personally seen the posi clutch issue you describe. Several folks on this forum have tried various modifications to add an upper link - some better than others. I personally don't like sliding yolks in the axle shaft due to friction in the splines that sometimes causes unpredictable geometry changes. With big horsepower and big tires you put a lot of twisting forces on the splines. I prefer stout CV joints on the axle to absorb the minor in-out movement. An issue with an upper link using a C-3 frame and a C-4 upright is the lack of room for the link because of the position of the frame rail. Also, it is fairly difficult to adapt an upper link to the C-4 upright, although several guys have built custom uprights or modified C-3 stuff to accept the link. The same thing applies to using C5 control arms without moving the frame rails inboard (see the Jag/C6 picture above)
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Old 01-08-2015, 06:25 PM
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SuperBuickGuy SuperBuickGuy is offline
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Quote:
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Quote:
Originally Posted by SuperBuickGuy View Post
The criticism I've heard - and I could blame for an issue I have/had with my car is this:

Since the driveshaft is a loaded member, on hard corners the force spreads the carrier thus reducing the ability of the clutches to keep both tires spinning.

true? false? but given what you've said - would you achieve the same benefit as a C4 suspension by simply putting an upper bar and removing the c-clip?

please excuse the sentence construction, it's probably as stuffed up as my head...
I have not personally seen the posi clutch issue you describe. Several folks on this forum have tried various modifications to add an upper link - some better than others. I personally don't like sliding yolks in the axle shaft due to friction in the splines that sometimes causes unpredictable geometry changes. With big horsepower and big tires you put a lot of twisting forces on the splines. I prefer stout CV joints on the axle to absorb the minor in-out movement. An issue with an upper link using a C-3 frame and a C-4 upright is the lack of room for the link because of the position of the frame rail. Also, it is fairly difficult to adapt an upper link to the C-4 upright, although several guys have built custom uprights or modified C-3 stuff to accept the link. The same thing applies to using C5 control arms without moving the frame rails inboard (see the Jag/C6 picture above)
I have a rear differential from an 06 GTO that 1320gforce built with all the good stuff (and it howls like a banshee) - so this questions comes from "I have this on the shelf" and is probably one of those "you could, but it would still cost more than other options".... despite that I'll plow on -

why not maintain the C3 arms, and replace the differential with GTO, Viper, or even new CTS/Camaro center then adapt the CV joints?
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