Thank's to Mr. Charlie @ TheSkunkWorks for getting me out of trouble several years ago with this same problem. His Two Cents worth was just the needed Fix. Happy New Year Mr. Charlie. Thank-you again. Gene

 

You're very welcome, sir.


IMHO a good deal of well intended tuning advice fails to account for how easily to over-prescribe rear anti-roll stiffness when one's own backside hasn't sat in the car in question while it is being seriously pressed. Besides, there's nothing inherently "wrong" with mild understeer on the street.


Anyway, glad to have helped before you departed us.

 

When I replaced my rear spring, I removed the bar that was back there and never put it back on. I believe I measured it once and it was the same size as the front. I don't see much change in the handling. '72 350 auto all stock 'cept rear spring.

 

A rear sway that's as large as the front sway would make for pretty scary limit handling.

FE7 has a 1 1/8" front sway w/ a 7/16" rear sway - tinier than the tiniest stuff I've seen come out of the aftermarket.

A lot of modern stuff runs bigger rear sway bars - they also tend to run staggered fitment tires so there's even more understeer built in than what our square fitment cars have.

At the end of it all, I agree 100% with what TSW said in his last post. The only point I really wanted to make to the OP is that the $$ put into a sway bar likely will not be worth it if the car isn't really driven aggressively.

If it is driven aggressively, you'll probably put more cash into a few different sway bars or an adjustable set up so that you can try to tune it to your driving preference.

 

A few more comments after reading some of the responses above:

Most cars made today do not run staggered tire setups to offset the bigger sway bars used on all cars today…only some high end sports cars..almost every mass market car on the road today runs pretty massive sway bars both front and rear relative to what GM was using in the 60/70/80's. Why? Because the best way to balance the chassis is through a combination of sway bars (FRONT AND REAR), shocks, Springs, and tires-All of them.

On the racing front…neutral to trailing throttle oversteer and light oversteer on the track is the preferred tack for the quickest way around the track…generally speaking-you help steer the rear with the throttle. Understeer is generally not a desired feature on the track. Most high HP cars regardless of origin will exhibit oversteer when the throttle is applied hard coming out of turns on the track.. 7/16 or 9/16 rear bar is not going to change that much.. The rear bar will effect to a greater extend the car's behavior under light to moderate throttle under light to high cornering forces.

Which brings me to the last point. Let's totally forget the effect of the rear sway bar under road racing or 10/10th street racing (which is generally not a good idea). The sway bar combo on any car including our C3's has the most dramatic effect on the feel of the car's handling and steering response 99.9% of the time just driving the car on the street-you do not need to be racing the car. The reason that my 2001 Pontiac Grand Prix FWD W body car has a massive 1.25 front GM factory bar and a 9/16 inch rear bar is NOT to go racing. It is because the car in everyday driving feels MUCH more stable in cornering than one without bars…It will understeer like most street cars at the limit. Think about this..why wouldn't GM just use a 1 inch front bar or smaller with no rear bar on this car? The same understeer trait could be achieved BUT the car would feel MUCH more under stable. Same with the C3…The 7/16 GM rear bar makes the gymkhana cars feel MUCH more stable on the street in everyday driving…nothing to do with racing just with how the car will feel 99.9% of the time.

Something that seems to get lost in these discussions…it is not just about racing and 10/10th driving when using the GM rear sway bar. Again…the factory GM setup on my 78 1 1/8 front bar and 7/16 inch rear bar will UNDERSTEER at the limit like ALL GM cars were designed to do in the late 60/70/80's-that is a fact. Removing the rear GM sway bar on a factory suspended gymkhana C3 will make the car understeer even more than with the bar.

 

Don't forget that the Grand Prix has a significant weight on the nose compared to our C3s. Modern Corvettes (going into 90's/2000's and newer) also have a tendency to understeer built into the suspension.

I agree 100% on throttle oversteer - asking more of the tires than they can currently do, while suspension does play a part - enough power can overcome any well designed suspension. I can do that in my 6000 lb truck if I try hard enough.

If you take the car out into the canyons and whip it back and forth - I agree that having better roll control is going to be great.

If you pull it out of the driveway, drive it to out of the burbs, onto the freeway, off the freeway, through down town, get to the car show and park it, I still say you won't be getting the money out of your investment.

BTW, if you want to know something really confusing, a lot of the C6Z guys who autocross disconnect their rear sway bars because it causes the car to have a tendency to understeer in "parking lot speed" events. Go figure.

 

Lest viewers forget, bear in mind that bars (front and/or rear) don't operate in a bubble, rather springs and bars combine to generate anti-roll stiffness. And, not every C3 is going to require the same total amount or F/R distribution of anti-roll stiffness to best suit its driver's needs, not to mention other variables. So it is that a given combination of bars won't always result in the same understeer/oversteer characteristics or satisfy every driver's preferences. This is why I typically refrain from making specific bar/spring package recommendations in favor of trying to help others better understand their workings and interrelationships within the bigger picture.


As for how near one must approach the limits for a car's true balance characteristics to matter, I respectfully submit that it is dangerous (if not irresponsible) to assume that one needn't worry about how their car will handle at 10/10ths just because they don't intend on going there. Doesn't matter where or how you drive, you never know when you might be put into a situation in which you find yourself hanging grimly onto the edge for dear life. One simply cannot presume how their car is going to handle at its limits based on what it does up to the point before it gets there. Many a car that will ultimately oversteer will seem as if on rails right up to the point of departure. Thus, I'd urge those who aren't dead sure of what they're doing and/or don't have a way to safely test their car's final balance characteristics should err towards a setup that would more likely understeer. You do NOT want to risk learning otherwise by surprise.


Also, IMCO "neutral balance" is somewhat a misnomer and largely unobtainable. No car will always loose traction at both ends simultaneously and to the same degree if/when its limits are reached during any and all phases of any and all types of turns. Weight transfer causes our corner weights to change during transitions into and out of each phase of cornering, which dynamically changes the traction limits at each tire at any one time. Braking forces, which use up a percentage of that traction, vary due to bias, how one engages and releases the pedal, and whether or to what extent one trail brakes. Same goes for varying engine braking and acceleration thrust. Then there are those bar things, which can significantly increase weight transfer while resisting roll (FWIW, springs don't carry that penalty while resisting roll). The role shocks play only multiplies these complexities. And, we haven't even mentioned steering inputs. Obviously, there are plenty of underlying nuances worthy of their own debate here, but I do hope my general point is easy enough to follow.

 

TSW - don't get me wrong, I agree w/ everything you have said in your post.

I would also like to posit that unless one has regularly driven their car at(or approaching) 10/10ths, odds are whatever condition demands they drive at that level will be dangerous anyhow.

And thank you for politely disagreeing with me.

 

FWIW, my intentions haven't necessarily been meant to disagree. IMHO we're on the same page more often than not, and not too awfully far off of it a good deal of the rest of the time.

 

Good discussion…

I think that many folks misinterpret throttle oversteer when evaluating a C3's handling characteristics….and the effect that the GM type rear sway bars (NOT the Aftermarket rear sway bars with non OEM GM end links which I feel are not appropriate to use with the C3 rear IRS). I really think that there is so much misinformation desseminated on this topic since many folks just don't understand vehicle dynamics at the adhesion limit of the rear suspension. Expecting a SBC C3 with a weight distribution of 48%F:52%R with an IRS (which is ideal for handling and racing) to handle like a 60/70/80's GM sedan or just about any other american made car of the time is totally unrealistic and NOT what GM wanted from the C3-they pretty much all plowed/understeered like pigs at the limit of adhesion. For 99.9% of drivers, understeer is the holy grail safety net of handling but believe me on the track and street, understeer can be very scary as well…think of a FWD car "plowing" heavily in the snow as you make a turn…Same on the race course, high speed turning and the car will NOT turn..Scary. Do not underestimate understeer..it is NOT to be take lightly either over oversteer..either one can be VERY dangerous.

Again, generally speaking, trailing throttle oversteer and mild oversteer is the fastest way around a road course…you do NOT want understeer. Understeer is easier to manage for the novice driver but let's keep that fact in perspective-it is easier to manage (safety) but not necessarily better (faster).

Then we have the occasional commentary from a C3 owner who have/had etc a rear sway bar and states the car was on an exit ramp and the rear "just" came around unexpectedly..generally for that to happen in a C3 or any car for that matter, the driver was going too fast, used drastic steering wheel correction movements, applied moderate to heavy throttle during the high g load turn breaking the rear tires loose, was using the wrong type rear sway bar,etc. Then often I read, well, I had this rear sway bar and immediately removed the rear bar and all was good..Hmmm. Well it became all good because now the car will understeer heavily and breaking the rear loose is more difficult--the safety net again but not necessarily a desired characteristic for a good handling sport car …..If folks are looking for a 70's GM cars that heavily understeer, buy a 72 Chevrolet Caprice and it will plow like a pig through turns.

Lastly, The C6Z06 is a slight to moderate oversteerer at the limit and VERY FAST on the track. The autocross guys disconnect the rear bar in slow speed autocross events to minimize mostly the throttle over steer that comes with 505 NET HP-it will help somewhat in that instance but will NOT eliminate throttle oversteer. I would not drive my 10C6Z06 at high speed road course events without the rear bar….

The bottom line of all of this discussion is that the C2/C3 corvettes were excellent handling sport cars for their time and even today are still very good handlers but like any great car require finesse, knowledgeable drivers of vehicle dynamics, and proper modifications made cautiously and judiciously….

 

When I'm autocrossing, push makes me very, very sad.

However - an unexpected push draws less adrenaline than unexpected looseness. Expected looseness though - that's all smiles.