I was wondering whether someone, with input from our huge compliment of engineers (and I would love to see a sensible discussion that I can understand and follow with the odd pic included) would venture to discuss the forces at play in the C3 rear and how different systems would interpret and counteract those forces.

It would be nice to learn the pros and cons of each system, so that I (and others interested) could make future decisions as to how to impliment and modify our C3's for the ultimate in driving experience.

I don't want to buy an Evo or a Ferrari! I want to drive my C3 with the smile it gives me every day, but just with the added twinkle in my eye for what it represents as one of the ultimate car-guy car's due to the added technology that our modern era has gifted upon us.

Sure, I can buy a complete bolt on suspension upgrade or make coil overs etc. with the help of our gifted friends on the forum.....

BUT..... I still don't know what either does but allow me to go around turns faster and lose the rear less often under the influence of that stab of the gas pedal.

.......That was way toooo long.

OK, please explain suspension forces under load to me

 

The main reason why I like coilovers is that it always you to do counterweighting, balancing weight on each corner. The other benefit is the reduction in weight, especially unsprung.

 

About 95% of the 'suspension' threads' on the forums are 'what suspension goo-gah shall I bolt to my car?' and 'is this suspension gizmo something I can throw money at?' and lots of quotes from catalogs or advertisements about how great this and that is with no real discussion of what the 'problem' is that is trying to be corrected.. I don't even waste my time reading most of these threads. But your inquiry caught my attention and struck a cord.

My take is radically different from the bolt-on/polyurethane crowd. Undoubtedly you're going to get a SLEW of comments about this and that to install and a few may even be from folks that know how to drive fast and can appreciate some of the mods that will be discussed. It is simple, cheap, methodical but requires patience.

1) Put GOOD tires on a STOCK C3. I don't mean the hard rubber crap tires that 90% of the C3s run and I dont' mean DOT legal racing tires - I simply mean good all around all-season performance tires w/ an H or better yet V rating. Hands down a C3 so equipped will run circles and circles around 5X the so-called suspension upgrades on a C3 w/ crappy tires. There is not a single upgrade, investment or modification that can trump the value of good tires. These are THE BEST BANG/BUCK PERFORMANCE UPGRADE period - bar none. And it's a safety improvement to boot.

2) Ensure the car is in good correct stock condition - the balljoints are good, the rubber bushings aren't shot, steering is to spec, the shocks are good. Etc. Essentialy a new or like-new condition suspension/steering/brakes in stock trim. None of the so-called 'trick' stuff like sway bars or colorful gizmos or whatever - just a good tight stock C3 base suspension beit restored, rebuilt or whatever.

3) LEARN how to drive a car, ANY car in a performance scenario. Try some autoXs. Or track sessions. Or school. Or SCCA. A stock C3 is capable of far more than the vast majority of bolt-on dudes' capabilities.

4) Develop a feeling for YOUR C3s characteristics and capabilities and YOUR ACTUAL USAGE and decide if it really needs any 'improvement' or correction. Do you want more oversteer? Is there a problem w/ bumpsteer? E.g. figure out what the specific problem(s) is FIRST THEN carefully select the mod(s) (if any) that may address it. (Mostl simply start here and start chucking money at radical suspension upgrades w/ no clue as to what they are doing or if any are truly necessary) Have you REALLY found the cars limits and need to modify it to go faster (Takes a LOT of practice to get there in most cases). I've seen guys swear they need to bolt a bunch of crap to their cars. Instructor gets in same car and takes owner for 'spin'. Cranks out time w/ no practice in specific car that might be 15% faster than the owners best. Obviously there was room for improvement but not where the owner thought...

 

hmmm, something tells me pgtr hasn't spent alot of time reading many of the detailed threads from the knowledgable people on this forum. maybe i'm wrong and if so, i appologize in advance.
having said that, i actually do agree with just about everything said above, i just figure those issues have been done to death. the reason i say that is in all the threads i've participated in regarding the c3 and handling, the number 1 improvement is always modern rubber. the other thing that differs is the common lament that there isn't bolt-on stuff to fix the c3 suspension.
aside from the modern tire connundrum, the most perplexing flaw in the front suspension is insufficient negative camber gain on compression. there are a number of lesser problems that exist on the front but let's return to your original question.
you want the brutal truth? the fact is the single weekest point in the c3 suspension is the damn frame. the frame should not act like a suspension member but, sadly, it does.
that being said, there are some things we can do (and many of us have done) to address the car's inherent weaknesses. first, gusset the frame as best you can. the chevy power manual you can find on-line offers places where the car can be strengthened. i realize this is a bit involved for those of us who don't desire to do a complete frame off resto or turn the car into a dedicated racer. however, you can spend some quality time underneath your mechanical mistress with a good MIG welder and some steel stock. straight weld every stitch weld you can get to and cover and weld as many holes in the frame as you can reach. i, for one, found one part of my frame that you could literally look straight through because of the factory holes.
that may be a bit more involved than what your looking for but that's the start.
sure you can install a fiberglass spring and better shocks and i'm sure that will help but any truely meaningful changes are simply not going to be bolt-on (except for the aforementioned modern tires).
back to your initial question regarding the rear suspension. probably the biggest design flaw with the rear is the toe change through suspension travel. the way the trailing arm is located, the rear tires go toe out under either compression or extention. anybody see a problem with this? surprise, you get both with heavy cornering loads. so your trying to turn in a sporting fashion and both rear tires are pointing outward. to compound this, one might think that you would want to design in total toe out (both wheels toe to the ouside of the corner being negotiated) but this is not the case. actually, for high speed stability and tractability, you would want both wheels to toe into the corner. this requires a bit of re-engineering to overcome. greenwood has apparently built a very nice 5 point rear suspension to alleviate this condition but it's rather pricy and requires some significant changes to the car. what you want to do to fix this problem depends on how much of a problem you view it as and how involved you really want to get.
one modification that appears to deliver alot of bang for the buck is a 6-link set up. this is really very simple by design and only modifies the stock suspension. the idea is to relieve the half shaft from its duty as a load bearing suspension member. an added benefit is increased u-joint and bearing life. the new upper link also relocates the upper a-arm angle to minimize some of that toe gain.
i've never been a huge proponent of the 'smart struts' bracket because i'm not sure it does much at all for toe change. the one thing it does do is reduce the amount of negative camber gain on compression, when you want it most. the problem with the ads in the VBP catalogs is that they always reference a '63 and the camber swing in that suspension. they fail to mention that that suspension was revised to reduce that camber variation by about 2*. in the typical c3 configuration, a rear suspension set at 0* camber will gain around 2-2.5* negative under compression (based on my measurements in my '81). too bad we can't get that up front, it would be damn near perfect.
o.k. so how's that for a long winded explaination?
short version: in the rear, eliminate toe changes under compression/extention. in the front, increase camber gain under comrpession.
those are the two biggest flaws in the suspension design of the c3. there are several others as i'm sure members will make you aware of, but those are the two that are the root of most suspension complaints with the c3. then, of course, like i said, we have a frame that is about as stiff as dry spaghetti. and that really doesn't help matters much.

 

Are you talking about the Greenwood or Guldstrand? I know both had one, but didnt think greenwood sold theirs anymore.
Guldstrand:
http://www.guldstrand.com/5bar.htm
Greenwood:
It appears that there are 2 different greenwood styles
http://greenwoodcorvettes.com/Street...nTurboAarm.jpg
http://greenwoodcorvettes.com/Street...a/FiveLink.jpg
http://greenwoodcorvettes.com/Street...on5%20link.jpg

 

The a arm suspension would be hands down the best solution but there's 1 problem, you need to seriously notch the frame and the storage boxes need to be cut out.

 

One thing I've not seen discussed either, from an engineering point of view, is the angle of the trailing arm in relation to the frame/direction of travel.

For optimum efficiency, I would expect you would want the center of the trailing arm bolt lined up with the center of the rear hub, so that when you accelerate, the force is transmitted straight through.

Let's say you lower the suspension so that it "looks good" or "has a nice stance". Isn't it likely that the arms are sloping down towards the trailing arm bolt? When you hit the gas, some force/energy/hp is wasted because it is not applied in the direction of motion. In this case, the rear end would want to move up a bit. (Put your index finger tips together and push)

I've not had a good look at it, because my car has been on jackstands, but isn't the goal to have the trailing arm horizontal at ride height? Both the rear and front springs, size of the tires, and the weight distribution would determine this. Or is no no way this can be achieved with the current geometry?

 

The angle of the trailing arm can affect the cars launch. It will push the car into the ground or raise it up.
I set my trailing arm/ half shaft with a small level and get the 1/2 shafts parallel to the ground.
For anything including sway bars to be most effective everything has to be is straight lines and 90 degree angles.
Try paddling a canoe. You need to paddle on one side then the other or twist the paddle before making the next stroke to correct for side loading. Same with the car , it needs a staight push to be most effective.

 

Guys this is what I did to my car to hopefully make it handle alot better. I believe it is the most tricked out suspension on the forum with Twin Turbo right behind and soon to pass.
For the front I used 1 1/2 inch longer spindles to raise the roll center for flatter cornering with light springs. It also makes the camber gain curve alot better.
I totally eliminated bump steer and I feel that is very important for rough roads. I welded all front seams and gusseted the proper places including filling in the hole for the ram in the frame, this is a very weak spot.
Bump steer involved alot of testing with different length tie rods and different center links. I ended up with 3 inch longer tie rods, so a 6 inch shorter center link and adding about 2 plus inches to the outer tie rod to move it down.
Lastly I went to coilovers for weight and easy spring change. It also lets me remove the springs/shock units for testing the front end.
Of coarse all bushings were replaced with poly and all joints replaced. A new free moving sway bar link was also added. The stock donut spacers will not work without binding.
I also bought about 6 pairs of springs for testing and tried every combination.
For the rear I went with the 6 link and coil overs with the front springs for testing also.
I am installing 10 x 18 rear wheels and 8 x 18 fronts along with 14 inch rotors, no proportioning valve and hydroboost.
To stiffen the frame I am actually working on right now a 8 or possibley 10 point cage
With 15 inch tires and no cage the car was absolutely stable at 130 mph where common sense made me quit. I ran this speed regularly but never exceeded it.
The only thing missing is the spreader bar which is on my list of things to do but that 3 inch blower belt is really a pain to run the bar.
Most of these mods Twin Turbo is already working on and his rearend setup will beat my 6 link.
So with the combination of blown 460 and good suspension I don't feel intimidated by anything out there up until my self impsed limit.

 

norvalwilhelm:
Just out of curiosity how well do you think your C3 handles compared to a stock C5 or Z06 now?

 

Since I never drove a C5 or Z06 I don't have a clue. When I started about 14 years ago my car even with all new suspension bushings, ball joints, tires and springs was still a dog and at 100 mph I almost lost it. Now 14 years later and many changes that same 100 mph over the worst conditions feels absolutely stable.
I also have nothing more to compare it to them my wifes supercharged Bonneville. It was a $43,000 car with performance suspension and her car's handling in hair pin corners, on the open road and brakes are far far inferior to my vet. My vet stays flatter in the corners, rides better on the open road and stops alot faster and stronger then hers. She even admits to the ride quality. She has 17 inch wheels and huge sway bar and that is all I can compare to.
I do know my car at 130 in no way feels like it is running out of control and gives you the desire to just push it faster and faster but fear of a massive ticket, jail and impounding of the car keeps me down.
I will not be outmuscled by anything on the road, my brakes pull me down from any speed without effort and hazzing the tires is effortless, locking up too can be a problem if I panic.
I don't know how it compared to anything else.

 

Point taken, and excellent post. No appology necessary - it is I that should appologize for aparently missing some potentially good discussions as I've been jaded by viewing more than a few superficial threads as well. If 'those' issues have been done to death - it seems a lot of people didn't get it. Sorry for any harshness on my part.

 

pgtr, excellent response and to you. i've been around this forum for a while now and have stopped replying to alot of threads because they are so repetative so i certainly understand what you mean. i'm not even sure why i hit this thread, except maybe that it rang close to home lately since half my rear suspension is out because of a diff failure.
still, i agree completely with what you said. i often advise people with c3's to take them to driving events. at the limit the c3 can be very unforgiving, at least compared to modern cars. even a *rustang* can be more easily driven at the limit than a vintage corvette. learn to drive one of these fast, and you can drive just about anything fast.
i have done a number of track events, primarily in the c3. i often find myself on track with c5's and porsches. i won't even pretend to tell you my car is as fast as theirs is but when i catch them in the turns, i'm either doing something right or they're doing something very wrong. these new cars really make some people feel like superman and they have no idea how often the car saves them from themselves. concrete barriers are a little humbling though.