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[C2] Front Coil Over Suspension & Rear Sway Bar

 
Old 01-24-2018, 08:55 AM
  #21  
woodsdesign
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Guys,
There is a lot of good information for me in this post. I appreciate all the feedback.
However, I want to be clear that my critical maneuver was not a disaster. I just expected better.
All my bushings are relatively new but I will check them over because you never know.
I really like working on my car and improving it's characteristics. If adding components that will do this then I am for it.
As for "catalog engineering" I have to believe that a lot of engineering time was put into developing these items.
Talking with several of these suppliers is impressive. However, it is always good to get input from people who have already been down that road.
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Old 01-24-2018, 09:26 AM
  #22  
SW Vette
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A little bit of oversteer is good (just ask any drifter ) but most mass produced vehicles are designed with inherent understeer to keep the less skilled driver out of trouble. That said, I wouldn't recommend re-engineering your suspension based upon the car's handling characteristics in an emergency situation. Much of that is determined by the driver's input, which is mostly reflexive anyway.

When it comes to a car's handling, any racer worth his salt will tell you the single biggest factor is tires. Even a small change in tire pressure can have a major effect on handling. Starting with the C2, Corvettes have been engineered to handle fairly neutrally. The best thing for any street driven Vette is to make sure the original shocks and bushings aren't worn out and replace them with OEM equivalent if they are, get some good tires on the car (like those Avons Duke recommended) and play around with tire pressures - experiment with higher, lower, changing front to rear balance - until you find the setup you like. It's simple to make a big change in how your car handles, and much cheaper than re-engineering the whole suspension.
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Old 02-05-2018, 12:52 PM
  #23  
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Originally Posted by SWCDuke View Post
The C2 base suspension is very "neutral", but can be twitchy at the limit and suddenly transition to oversteer on trailing throttle or with very quick steering inputs.

Tire construction and front camber have a big input on steering response. Going negative on camber will improve it, but increase oversteer bias. This can be mitigated by replacing the front rubber anti-roll bar link bushings with hard urethane bushings.

If the car still has too much transient oversteer bias, replace the OE 3/4" anti-roll bar with the 13/16" bar that was used on C3 base suspensions beginning circa mid seventies. A larger front anti-roll bar will increase front roll stiffness and understeer bias, and the increase in roll stiffness is a function of the fourth power of bar diameter, so even a 1/16" difference in bar size will have a noticeable effect on transient and steady state dynamic response.

Also, having about 1/16" rear toe (with radial tires) EQUALLY DISTRIBUTED SIDE TO SIDE IS CRITICAL TO STABLE HANDLING! So when was the last time you had the car's alignment checked?

Case in point. I was helping the owner of a 15,000 original miles '67 L-71 prepare for a PV. I tested steering response with short, but quick steering inputs to test stability. Right was fine, but left resulted in definite rear instability in the form or oversteer.

So I said the alignment, particularly rear toe, needed to be checked. The LR toe-in was about 1/16", but the right was 1/8" TOE OUT! No wonder the rear wanted to step out with a quick left flick of the wheel.

Given the low miles I figured that the shims were as installed by St. Louis. So how did the RR toe end up so far out of spec? I could only guess, but my best WAG is that the operator installed the RH trailing arms shims "backwards" i.e. he installed what should have been the inside stack on the outside and vice versa.

Case number 2: My 1976 Cosworth Vega. In OE form it had excellent steering response (even with the junky OE Goodyear radials that had a habit of disintegrating without warning) and was dead neutral up to the limit when it would transition to oversteer. With a little help from Fred Puhn's "How to Make Your Car Handle" I figured out the problem and an easy solution. The front bar like most GM cars had compressible rubber bushings on the bar to control arm links, but the rear bar was solidly bolted to the trailing arms. So what was happening is that increasing lateral g caused increasing roll, which further compressed the link bushings, reducing front roll stiffness. This reduced front/rear roll stiffness distribution to the point where it caused the car to transition to oversteer just below the ultimate adhesion limit.

The solution was to replace the OE rubber anti-roll bar link bushings with the hard urethane bushings that were OE on Pontiac Trans-Ams.

From the early eighties to late nineties I ran this car in track events at Riverside and Willow Springs (on better tires). People who rode with me were amazed at how neutral and forgiving this car was. I could keep it at the ragged edge of adhesion in a slight four-wheel drift in the big sweepers with just minor steering and throttle adjustments.

I did add 1/16" larger front and rear bars along with Spax adjustable shocks. This took about two years at four events per year making one change at a time before it was fully dialed in, and in the early nineties I installed a set of real DOT legal racing tires - 205/60VR-13 Toyo Proxes RA-1s to replace the Phoenix Stahlflex 3011s I had used previously, which were the hot setup in showroom stock racing going back the the late seventies.

I never lost control of it on road or track, but in the process embarrassed a lot of name brand sports car (like beginning with F and P) drivers. A lot of them were way faster down the big straights, but could not out-brake or out-corner me to such an effect that my "Vega" turned better lap times.

So before you spend 2500 bucks on a suspension" upgrade", get the alignment checked and corrected as necessary and apply the tuning tricks I recommended above if you want to experiment further at little cost.

Over the years I've talked to many aftermarket suspension outfits, and when I stated asking some basic vehicle dynamics questions like ride rates and roll stiffness distribution, they all went catatonic. Clearly, none of them had even a basic understanding of vehicle dynamics. Like many aftermarket cam manufactures it was all about "bigger is better" - duration and overlap or spring rates and anti-roll bar sizes.

I don't know if Puhn's book is still in print, but I'm sure you can find serviceable used copies on the Web. Unless you have a sound background in vehicle dynamics I strongly suggest obtaining a copy before you spend one thin dime on "suspension upgrades". It's written for the average amateur car enthusiast/racer, so you don't have to have an engineering and math background to understand the basic principles.

Basic principle: if you want to increase understeer bias/decrease oversteer bias, increase front roll stiffness with stiffer springs and/or a bigger bar and vice versa if you want to reduce understeer/increase oversteer, and fine tuning an be done with camber adjustments. If you can grasp this principal, you will understand that increasing rear roll stiffness on a small block C2 by adding a rear bar will create an oversteering beast unless you compensate by installing an appropriately bigger bar on the front.

Throwing money at a problem will never solve it unless you understand, at least at a high level, the underlying physics. Example #1: federal, state, and local government!

Duke
FYI, Just bought Freds book on Amazon. Thank you for enlightening me as I move forward with my rebuild.
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Old 02-05-2018, 05:09 PM
  #24  
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Before finalizing any thoughts on especially a rear sway bar, do drive the car first and test the tire adhesion in a high speed radius turn, have someone watch you take a tight turn at speed to see body roll at the back. Drive the car to see if it is understeering or oversteering in general. Then go forward from there. Then put one on and repeat the tests.

Last edited by TCracingCA; 02-05-2018 at 05:10 PM.
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Old 02-05-2018, 05:14 PM
  #25  
woodsdesign
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Originally Posted by caskiguy View Post
FYI, Just bought Freds book on Amazon. Thank you for enlightening me as I move forward with my rebuild.
I also bought the book. It has a lot of good info. I plan to read it before doing anything to my car.
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