C3 Over Camber

Ralphy

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Question: Has it ever been written or personally diagnosed. That a C3's rear suspension over cambers while cornering? I have seen kits that lowers the camber rod on a C4. However I have never run across anyone discussing or complaining about the C3. The first reason I have for asking this is that I have a narrowed setup, 1" per side. My thinking is that this alone would increase camber. So because of this I was wanting to lower my inner CR's slightly, app. 1/2".:bullshit:?


Ralphy
 
smart struts (adjustable strut rods) and a lowered centeer bracket are available from VBP :thumbs:
 
The real issue is toe control and as a result, toe steer from the toe going to out when the suspension moves. This because the camber rods are at theur longest horizontal length when horizontal of course, any deviation from that makes their effective length shorter and this pulls the rear of the trailing arm inboard, causing toe out.
 
The real issue is toe control and as a result, toe steer from the toe going to out when the suspension moves. This because the camber rods are at theur longest horizontal length when horizontal of course, any deviation from that makes their effective length shorter and this pulls the rear of the trailing arm inboard, causing toe out.

And I blame that toe for almost causing me to tow, but I got lucky, don't you know.....:lol::lol::sos:
 
TT, with some quick measuring I did some weeks ago. The distance between the half shaft and camber rod is 2" greater at the wheel vs. at the diff. So static the camber rod is not at it's longest point. However the half shaft is and being even shorter, it's arc is faster inward then the camber rod. So it's mainly the half shaft that causes the toe out I think. If you lowered the camber rod as with the Smart Strut it would be flat out!

Anyhow are you suggesting if I corrected the toe issues. I can disregard and not be concerned about camber?
 
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This brings back memories, Marck might remember we've had this very same discussion back in 2004/2005.... took me a while but I understood... regardless of camber the toe still changes because the wheel moves in/out during suspension travel. the further the susp travels the more toe out you get.

This very same travel or rotation is what's killing the poly trailing arm bushings, the stock rubber allows this rotation of the trailing arm with almost no wear on the bushings, poly can't handle it over a long time....
 
One other negative is that it shortens the wheelbase. Through some searching I saw a guy selling a kit to fix the early 2000 Mustang IRS. Claiming it toed the wrong way, and that was in. He said toe out is better for performance. His web store was shut down. He had some numbers charted as to how much toe the Mustang had. It was app. .3 degrees for 2" of travel. Before and after were exactly opposite he went to .3 out at 2" travel. I'll try to find it.

Well I found it under my favorites, however it's dead now. Though the chart was interesting because I have never seen actual numbers on toe. Wish Pierre could chart his setup.
 
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TT, with some quick measuring I did some weeks ago. The distance between the half shaft and camber rod is 2" greater at the wheel vs. at the diff. So static the camber rod is not at it's longest point. However the half shaft is and being even shorter, it's arc is faster inward then the camber rod. So it's mainly the half shaft that causes the toe out I think. If you lowered the camber rod as with the Smart Strut it would be flat out!

Anyhow are you suggesting if I corrected the toe issues. I can disregard and not be concerned about camber?

With regard to what Marck said, I think you're confusing a few things. He was specifically addressing the weird toe change our suspension goes through during its travel. While not exclusive, this has less to do with halfshaft vs. strut rod length. Our suspensions effectively make two A-arms with a single common point, that being the front pivot point at the front of the trailing arm. For the upper, the other two points are the inner and outer half shaft yokes. For the lower, the two strut rod points. Since there is no other means of controlling toe, it is solely dependent on what the trailing arm does. Now the toe, in theory, is set at 0 static, but any movement of the suspension in either direction results in an immediate and proportional increase in toe change off center. This induces a bunch of wonky handling issues. The fix came with the c4. A major improvement was the use of dual links to replace the single trailing arm, giving the car a much longer effective center point for the front pick up. While the actual pick up points were relatively unchanged from the c3, the effective pick up point of the new configuration moved the point at which the two a-arms intersect much closer to the front wheel. That does a lot for minimizing the changes in suspension through its arc of travel. Secondly, the hub was isolated from those links and instead relied on a toe rod connected to the rear of the differential carrier in parallel with the halfshafts to maintain the toe settings throughout the arc of travel. This cured a bunch of the inherent "rear wheel steering" inputs designed into the c2/c3 platform.
Now as far as camber is concerned, the c4 design is still very similar to the c2/c3 design. Building in a little controlled camber change in cornering can be a very desirable thing. I'm not sure what you mean by "overcambering". I know the drag racers like the Smart Struts because they remove the camber induced during suspension compression (squat) at launch. That squat rolls both tires in at the top, reducing the amount of tread in contact with the pavement at the worst possible time.
However, that "problem" is actually far more desirable in high speed cornering. The outboard tire will camber negative (in) as the suspension compresses and the inboard tire will camber positive (out) as the car rolls toward the outside of the turn. When dialed in, this can be a very good thing by maximizing the amount of tire that maintains contact with the pavement throughout the arc of the turn.
Hope I don't sound like I'm talking down to you (or others) I just don't know how much you understand about the suspension dynamics. For the record, most of what I know I've learned here and reading suspension books, and half of that is probably wrong.
 
I was responding to TT's statement, "This because the camber rods are at theur longest horizontal length when horizontal of course, any deviation from that makes their effective length shorter and this pulls the rear of the trailing arm inboard"

My point being the camber rod is app. 2" below center at the hub. So during the squat motion it is actually still moving away elongating. However the half shaft sits pretty much horizontal. So during squat it's the motion inward that gives the toe out. I think you may have briefed over the posts a little fast.

Then there is the hammering of the rubber control arm bushings that cause the TA's to yaw all over during acceleration and deceleration.

Another point you have missed in your explanation of the C4 is the ability to toe the rear wheels in during jounce and out at rebound giving toe/steer. Since the rear link is longer then the half shaft. Then there are the two forward links positioned as to allow the rear wheel some deceleration going over bumps. Plus the two forward links increase wheel base under jounce unlike the C3 that shortens wheelbase......................But if you.............
 
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Alrighty then. No offense intended. I'll kindly butt out.

yea, what could someone who has actually extensively tracked one of these things possibly have to offer? As you say we decided a long time ago the smart struts are junk for cornering. You want to gain as much negative camber as possible under compression. The bracket is a piece of shit too. The bolts keep loosening up.

I did an experiment at Calabogie and cranked in about 5 degrees of negative camber on the rear wheels only. The thing never felt so stable ever. It needs lots of rear camber. The tendency for rear toe steer is not a big deal with me as long as the rear stays planted. You have to learn the quirks and drive through them. It just takes more skill than driving a c4,5,6.
 
Alrighty then. No offense intended. I'll kindly butt out.

yea, what could someone who has actually extensively tracked one of these things possibly have to offer? As you say we decided a long time ago the smart struts are junk for cornering. You want to gain as much negative camber as possible under compression. The bracket is a piece of shit too. The bolts keep loosening up.

I did an experiment at Calabogie and cranked in about 5 degrees of negative camber on the rear wheels only. The thing never felt so stable ever. It needs lots of rear camber. The tendency for rear toe steer is not a big deal with me as long as the rear stays planted. You have to learn the quirks and drive through them. It just takes more skill than driving a c4,5,6.

You're absolutely correct!
I was amazed at the superhuman driving skills of the "rich" guys when the C4s first came out. I was working like a dog to do quick laps in my '69, and the C4s were still beating me. It wasn't until I bought my (used) Z51 '84 (to tide me over while I had the '69 torn apart) and ran my first autocross with it that I found out the "secret". You could put a trained chimp behind the wheel of a C4 and go fast (I haven't track driven a C5 or C6, but I'm betting the chimp could go quick in one of those too). The C4 suspension is just a giant leap better than the C3 configuration.
 
Alrighty then. No offense intended. I'll kindly butt out.

yea, what could someone who has actually extensively tracked one of these things possibly have to offer? As you say we decided a long time ago the smart struts are junk for cornering. You want to gain as much negative camber as possible under compression. The bracket is a piece of shit too. The bolts keep loosening up.

I did an experiment at Calabogie and cranked in about 5 degrees of negative camber on the rear wheels only. The thing never felt so stable ever. It needs lots of rear camber. The tendency for rear toe steer is not a big deal with me as long as the rear stays planted. You have to learn the quirks and drive through them. It just takes more skill than driving a c4,5,6.

You're absolutely correct!
I was amazed at the superhuman driving skills of the "rich" guys when the C4s first came out. I was working like a dog to do quick laps in my '69, and the C4s were still beating me. It wasn't until I bought my (used) Z51 '84 (to tide me over while I had the '69 torn apart) and ran my first autocross with it that I found out the "secret". You could put a trained chimp behind the wheel of a C4 and go fast (I haven't track driven a C5 or C6, but I'm betting the chimp could go quick in one of those too). The C4 suspension is just a giant leap better than the C3 configuration.

OK, I think I can understand that with the REAR suspension....

much different for the front?? or are the differences relatively minor??

tempted to do a C4 rear suspension IF it brings that much more to the table...

as the typical 'smart strut' or later shark with adjustable strut rods goes through it's swing, how much toe is changed?? the way it sounds like 15 degrees or something....but what IS it? 3 degrees?? that don't sound like much to me, and makes me question that if the C4 rear suspension can really make improvement to my hotrod '72....
 
It's not just a question of how much of a a change. But how much in the wrong direction. My rough calculations come up with a need of about 1/3 degree at 2" travel or .300 degree. If someone with a C4 could remove their spring and shoot a laser at a wall. Then measure and trig it out we could find out. This is a well kept unknown. Have you ever driven a fork lift and noticed how the ass end whips around? That's what a C3 does in a narrower scale. Also the toe is not produced from the strut, it's produced from the half shaft.
 
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Outer toe link.JPG

81260021.jpgOkay, I'll jump in here since I have some experience with this issue -- been there, done that, and have the pictures to prove it. I put a C-3 rear suspension under an early Vette a number of years ago. More recently, I removed all of the C-3 components except for the differential and added modified C-4 components. At one point I had the C-3 suspension on one side and the C-4 derived components on the other. I spent a lot of time with the laser and a bump steer gage comparing the two. The C-3 suspension gives toe out roll steer with either jounce or rebound. Basically, the wheel hub moves inboard toward the centerline of the car as the the half shaft swings through it's arc (up or down), but the forward end of the trailing arm remains at a fixed distance from the centerline. Since the wheel hub is rigidly aligned with the trailing arm, the result is toe out with roll (or suspension compression on acceleration or deceleration). Toe out with roll makes the car loose and causes oversteer which can be compounded by a heavy throttle foot. When GM built the C-4, they "untied" the wheel hub from rigid alignment with a control arm by adding two forward links with bushings at each end. This meant you needed a toe link to control toe in/out, much like the tie rods in the front suspension. And like the front suspension, the rear is subject to bump steer based on the length and up-down angle of the toe link. Note that GM made the C-4 rear toe link longer that the half shaft which means it swings in a larger arc, and, consequently, causes toe in of the rear tire with roll -- the opposite of the C-3. This was really a consumer safety issue in that it kept the car from getting loose (oversteer) on an on-ramp so the idiot driver would push into the wall and hit it with the front of the car while scuffing off speed instead of swapping ends and backing into the wall or oncoming traffic. You can control the amount of toe in by raising or lowering either end or changing the length of the toe link, just like you adjust bump steer on the front suspension. As far as the discussion of the smart struts goes, I will add my 2 cents. Lowering the inboard end of the strut rods does minimize camber gain, but more importantly it lowers the roll center of the rear suspension. This means you need more spring rate to acheive the same roll resistance. Note that C5 and C6 Corvettes have very low rear roll centers and big springs and huge rear sway bars. They also have very little camber gain for two reasons -- they don't roll much because of the roll center/springs/sway bars, and as you have camber gain with 14 inch wide tires with short, stiff sidewalls, the inside edge of the tire acts like a fulcrum and picks the outside half of the tire tread up off of the track -- not good. Tires have an optimum camber angle under maximum cornering performance (generally around 1.5 degree for high performance radials), so the supension should be designed to add just enough camber to keep that optimum angle as the car rolls.
 
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