NewbVetteGuy

Modernizing the suspension / handling components of our C3s can get just insanely expensive. I finally STARTED attempting to begin trying to understand handling/ suspension but I'm sure there's years more worth of knowledge to acquire in the meantime I'm trying to understand some of the important and good bang-for-the-buck improvements that can be made to our C3s.


#1. Modern High-Performance Tires
#2. Modern High-Performance Shocks

After #1 and #2 things get murky; particularly prioritization.
I understand there are a number of price points that can result in a well-balanced total package that you need so I'll throw out there that personally, I'm looking in the VB&P Street & Slalom package price category.


Other important suspension/ handling items to address on C3s (in no particular order because I don't understand enough to have this list prioritized):

• Stiffen the frame- there's lots of places this happens in the list below and a great many more not mentioned (spreader bars, sway bars, solid motor mounts, etc..)
• Spreader bars- help to stiffen the frame but also reinforce it and get the front-end camber back closer to where it should be
  
• Rear camber- the C3 rear end also suffers from difficulty getting proper modern camber specs, especially when lowered; the stock rear end "cams" also can easily lose their already compromised camber settings in spirited driving. Adjustable strut rods and getting rid of the stock alignment "cam" is the order of business here. -Rear camber being off will also cause excess tire wear and reduced traction- rear camber being off will reduce straight line and cornering performance.
  
• Rubber bushing steering deflection- I'm not sure exactly what bushings are the most important here but deflection of forces from rubber bushings can make cornering response less responsive and unpredictable; poly bushings (graphite or teflon impregnated to prevent binding and squeaking) can help as can moving to solid connections such as heim joints.
• Appropriate (For driving style) and matched spring rates, sway bars, and shocks: Spring rates (Front and rear), sway bars and shocks should be thought of as parts of a SYSTEM and should not be mixed and matched ***** nilly. Sway bars increase the effective spring rate of the front-end or rear-end springs. Straight-line performance / drag performance and cornering performance / autocross suspension setups are very different and if you optimize for one application too much the other application will suffer.
• Counter-acting from-the-factory understeer- Our cars, even with the Gymkhana suspension package are setup with understeer; a balanced and matched suspension system (springs, sway bars, & shocks) is still required but moving the balance to neutral or a slight oversteer is preferred

What did I get right? What did I screw up?
Are there other important parts that should be upgraded/ addressed even with a fairly minimal budget?


Adam

MelWff

You probably realize your number 1 requires going to 17" or larger wheels.
I think you first have to decide on your bullet point marked, "Appropriate (For driving style) and matched spring rates, sway bars, and shocks"
Are you going to autocross or go to a local road course?
What are the conditions of your local roads during the seasons you intend to drive, lots of potholes are going to make you regret overdoing suspension stiffness.
I went with 17" wheels and modern summer only tires. I installed Konis along with a composite spring years ago, but today would probably go with Biltstein HD. I installed a front spreader bar and larger front sway bar and added a rear sway bar. I'm in the North East and due to the roads do not regret sticking with rubber bushings.

NewbVetteGuy

Specific application time:

I've got a 1979 L82 Gymkhana with a from-the-factory curb weight of 3,650 lbs (every option except for CB and rear window defroster); I already put 245R 18" wheels on it (yes, I regret the 245 width; should've gone wider) and have a 360lb 1/2" shortened on each end VB&P Composite rear spring with a set of 8" and 10" bolts to install. I've also got the SpeedDirect spreader bar I hope to get installed today.

I've looked closely at the VB&P Street and Slalom kit and I think that's roughly where I want to go with things; I also looked @ jb78l-82's setup which also seems inspired by the Street & Slalom kit.



I'm thinking that I'm going to want to get Bilstein Sport shocks as soon as I install the VB&P 3360lb rear spring.

Then my car comes with a 1 1/8" Gymkhana front sway bar so it seems good to keep it and then just replace the stock whimpy 7/16" rear sway bar with a 3/4" one-- I see some people referring to "OEM-style" rear sway bars but I don't really know what that means, nor what the alternative is.

Eventually my plan is to replace my gymkhana 550lb OEM front springs with the 1" lower VB&P 550 lbs spring, but with quite a bit of weight reduction going on in the front, I wonder if the 550lb will be too much particularly as I cut it down a bit lower still to get the front end down...

I'm pretty sold on graphite or teflon impregnated poly bushings almost everywhere.

I've been thinking of getting the VB&P smart struts, but I have no idea whether to go all Poly, 1/2 Poly & 1/2 "HD" ends (whatever HD ends are...), or HD ends only -or go with an alternative with Heim joints...


One of the Guldstrand-inspired cross member reinforcing kits seems like a good idea at some point, too.


Adam

jb78L-82

I am in the northeast as well and my 78 with poly everything including upper and lower control arm bushings, 550/360 springs, spreader bar, competition adjustable struts with heim joints etc rides BETTER by far than the gymkhana or base suspension GM components. I have to say that a MUCH softly sprung C3 would absorb bumps/rough roads better than my suspension, but really is not practical for a c3 since the car would wallow and float all over the road so the trade off is just not worth that type of suspension. What you get with a solid suspension baseline is a firm feel that does not feel like the chassis is connected to a rubber band, firm but not harsh. A base suspension C3 with OEM components rides much harsher than my 78 and very truck like...

With all that said, modern cars with stiff, solid chassis's are able to make the suspension much stiffer with moderate loss in ride quality...another words any thing that you can do to tighten the suspension on a C3 (poly control arm bushngs, spreader bar, heim joint struts etc) will allow stiffer springs and shocks with minimal loss in ride quality...

The above is the reason that my 10 C6Z06 with stock suspension except DRM Bilsteins, my 12 Lexus IS350 F Sport, and Chrysler 300 V6 with Bilsteins all around, front Mopar strut brace and Eibach front/rear Hemi V8 sway bars are stiff but not harsh riding. Same for the 2001 Grand Prix with Police Struts, front and rear strut tower braces, GM performance front and rear sway bars, GM performance trailing arms and the car rides REALLY nice...firm again but not harsh.

Just another viewpoint.........

NewbVetteGuy

jb78L-82,

The one thing I can't understand from your setup is why Bilstein HD's on the front and Sport on the rear. I understand that the composite rear spring requires a shock that can keep up with it (Sport, not HDs).

I saw a thread where you went into how you setup ended up the way it is and my understanding is that you bought HD's initially and found that the rear composite spring required Bilstein Sports so you swapped the rear HDs for the Sport- is this about right?


(I'm wondering about whether to use Bilstein Sports all the way around or do the same HDs in front, Sport in rear thing that you did.)


Adam

jb78L-82

Adam,

You are spot on...had HD's all around initially but needed Sports for the 360 composite. The front 550's are very stiff to begin with and I felt that the HD's on the front already were more than adequate with the 550's...since the springs are very stiff to begin with, you do not need a shock with as much damping as the Sports....Worked out great for my setup...To be honest, I don't think that Sports all around is going to be that different than my suspension with 550 front springs with Sports versus HD's

Metalhead140

I started at the same spot as you, '79 with factory gymkhana suspension. I wanted to dramatically improve the handling without spending too many $. I rebuilt everything last year and I'm very happy with how it turned out. I intend to do some hillclimbs and track days (have done lots in the past, but not yet in the Vette). My background is mostly with modified light, good handling, unassisted rack and pinion British sports cars, so perhaps my tolerance for ride is higher than most? Regardless, I think my Vette, though fairly stiff, rides very well.
- Energy Suspension poly bushes throughout
- Moog ball joints, idler arm, tie rods etc
- Bilstein Sport shocks front and rear
- Global West tubular upper arms (for improved caster, and camber curve)
- 1 coil removed from front factory gymkhana springs
- Borgeson steering
- Shortened factory gymkhana rear leaf (for clearance for my 17"x9.5" wheels) with 8" bolts to lower ride height
- Relocated handbrake cable on top of trailing arms (for clearance for my 17"x9.5" wheels)
- Rebent rear sway bar arms (for clearance for my 17"x9.5" wheels)
- 1/2" Spacer (and longer bolts) fitted between diff centre and strut to bracket to improve rear camber curve.
- SpeedDirect spreader bar
- Ridetech steering box brace
- Solid engine mounts
- Aggressive suspension and steering alignment
- 17x9.5 wheels, 255/50r17 Nitto Invos

I think the car drives great. I wouldn't suggest going to a larger bar on the rear straight away, especially given your planned hp increases, you may find it unnecessary. I haven't had it on the track yet to see if I want a bit more stiffness in the rear on a fast sweeping corner, but it certainly doesn't feel understeery on the street. My next upgrades would be a glass rear spring (as much for weight as anything) and I will fit heim jointed strut rods when the bushes wear out (budget was getting thin at that point and I had the complete car Energy Suspension bush kit), and I also want to do the solid diff mount and relocation. But I really don't see any need to upgrade at this point, I'm very happy with it. I may fit a lower pressure valve to the steering pump to reduce assistance as I'm used to driving vehicles with unassisted steering, but it's certainly not necessary.

Edit: I strongly suggest reading the Vette Improvement Program articles. You can find them here: http://corvette.wikia.com/wiki/Suspension

TheSkunkWorks

I should hope that use of the term "neutral balance" is accepted as being somewhat a misnomer for what we really want a car to do in the real world. How a car transitions into and out of any steady-state cornering is at least as, if not often more important than its balance while the suspension has taken a full set. One end or the other is most likely to let go first, rather than both ends at once - which one highly dependent on what phase of cornering is in question as well as how the driver is dealing with and/or reacting to it. Also, based on having done many a road racing mile, IMHO final oversteer is highly overrated, particularly when enough excess power is on tap to readily induce oversteer with throttle application. In any event, I urge to never assume how a car is going to react at 10/10ths of its true limits based on characteristics shown when operated under tamer conditions.

As for additional tweaks and recommendations, I'd begin by reading up on the Chevy Power Book's [C3] Corvette Section. Then, whatever you ultimately decide to do with that info, dropping the rear inner camber links to 1/2" lower than their stock relationship with the diff is a sound baseline setting for reducing rear camber gain (level the struts with the half-shafts for the strip). Further, tho it's not that a simple task, I'd give strong consideration to setting rear static ride height to locate the inner u-joints 1/2" above the outer u-joints in order to limit the ill effects of rear toe-steer inherent to the C2/C3 IRS. Note that depending on what ride heights you ultimately land, this may require raising the diff in the chassis, but getting this geometry right is worth doing if you tend to press hard very often. I'd definitely address front bumpsteer as well.

Finally, and despite those who always seem to be peeved by my saying so, better IMCO to increase spring rates (in as much as doing so is practical for the roads on which you most often drive) in order to achieve a desired balance, rather than to rely on increasing bar rates. This is particularly so at the rear, where it is entirely possible (even preferable) to eliminate bar altogether. I'll go into the whys and wherefores upon request, but if you think of bars as more of a crutch than a primary tool, and you've got the idea.

In any event, I'd advise viewing any pre-packaged kit as only a starting point from which to work towards you goals instead of believing you're likely to hit the bull's eye right out of the box. My $.02, and good luck.


TSW

NewbVetteGuy

Hmmm.. I don't even totally know what upper A arms actually do right now; I didn't know that aftermarket upper arms were required for improved caster, but most of what little time I've spent looking at suspension was focused on packages and the rear of the car.

I'll need to look into this more.

I've considered this, too but I don't want a 550lb front spring to get even heavier especially with the coming wave of weight reduction up front and for $40 each I can get the 1" shorter VB&P springs so I've been thinking of starting there. -If I could find 460lb front springs that were the same height at the VB&P 550s; I'd probably go that route.

I just cannot deal with sloppy, granny car steering so I went nuclear and got the Steeroids rack and pinion- it's odd at low RPM; I think either my power steering pump is getting close to dying or it's 900-950 lbs of pressure just isn't enough for the Steeroids kit which wants 1050-1100 psi .


I got lucky here; my Bowtie Overdrives 4l60e cross member includes a relocated handbrake bracket (it's still pretty close to the drive shaft, but has JUST enough clearance).


This I've also never heard of; I've now heard of people both raising and lowering the diff so I'm not really clear on this at all. Do you have a link to a picture / the part(s) that you used to accomplish this?


I never thought that HP / torque level would impact the decision to go with a particular rear bar diameter; I'll put this item to the bottom of my suspension list, then until I get all the motor stuff done.

Obviously you have the Borgeson conversion and I've got a rack and pinion, but we're on opposite ends here right now; I'm considering replacing my power steering pump with a higher pressure model or doing the pressure mod to increase the pressure on mine. (even an overdrive pulley to improve flow at low rpms). -I'm definitely not happy with mine at low RPMs; it feels like the power steering cuts in and out- I thought it would be u-joint binding but I checked this out over the New Year's holiday and although a bolt comes close to hitting the headers, there's plenty of clearance and no binding whatsoever.


[/QUOTE]

I read it before but need to go back to it again now that I understand what a few more pieces of the suspension do and what some of the limitations of the OEM equipment are.



Thanks again!

Adam

NewbVetteGuy

Awesome distilled wisdom; I probably understood half of it, but I'll keep coming back to it!

Great to understand that I should focus on spring rates primarily and bar size secondarily to "tweak" the spring rates. -I think I'll leave the stock swaybars in place until I get all the engine work done and then evaluate whether I need a bigger rear bar and if so, how much.


Adam

MelWff

Originally Posted by Metalhead140 View Post
- Relocated handbrake cable on top of trailing arms (for clearance for my 17"x9.5" wheels)

I got lucky here; my Bowtie Overdrives 4l60e cross member includes a relocated handbrake bracket (it's still pretty close to the drive shaft, but has JUST enough clearance).

You are misunderstanding what Metalhead is telling you. It's not the handbrake bracket, its the rear suspension trailing arms which have the cable on the outside of the arm causing interference with wider wheels/tires.

NewbVetteGuy

Ahh; thanks for the clarification; get it now.


Adam

Metalhead140

The tubular upper arms have better geometry allowing increased caster (they set the upper joint further to the rear) and an improved camber curve (increased distance to upper joint).

I personally think shocks and tyres are a bigger contributor to ride than spring rate. My car rides better than it did when I bought it. Most modern sporty cars are pretty stiff (spring rate) but still ride ok. Keep in mind that the actual wheel rate (effective spring rate at the tyre) is about half the spring rate on the front of our corvettes. This should be apparent looking at the suspension - the spring seat, located approximately half way along the lower arm, sees roughly half the movement that the wheel does. This means much higher spring rates for the same effective wheel rate as a car with Macpherson strut suspension for example, which have a near 1:1 relationship between spring rate and wheel rate. Heck, I run 450lb front springs in my MG Midget which has a similar front suspension design to the Corvette, and weighs less than half as much (~1450lb, yes, it's a very small car!).

I agree, and my plan was for rack and pinion too initially, until I read several people who had converted from rack and pinion to Borgeson and felt there was no detriment in feel. This combined with reduced steering lock from the rack and pinion and the odd report of broken mounts, along with the closer to factory look and reduced price, swayed me to the Borgeson.

As someone else posted, this is not what I am referring to, but where the handbrake cable travels over the trailing arm. The handbrake cable normally sits between the trailing arm and the wheel/tyre, in this space here (not there as already relocated, this shows the increased clearance):



Here's a photo I took during the process of relocation. You can see the shiny lines on the side facing the camera where I cut off the handbrake cable bracket, and where I am relocating it on the top of the arm:



This is not about lowering the diff, it's about lowering the strut rod bracket relative to the diff. I believe that most of the aftermarket 'competition' strut rod assemblies have this geometry change built into the strut rod bracket. I still want to raise the diff (in conjunction with this mod) at some point when I get to it. I just made a 1/2" thick plate to go between diff and strut rod bracket and then used longer bolts to secure it.:



A lot of serious racers forgo the rear bar altogether. Better in my mind to increase front grip rather than decrease rear grip (which is what a larger rear sway bar does), and with increased horsepower you have the ability to oversteer at will with the right foot, so having a slight understeer tendancy allows you to balance the car on the throttle in a corner.

No worries, hope it helps!

jb78L-82

This link is really very good at explaining the pros and cons of sway bars, good reading for all:

http://www.turnology.com/features/la...yre-important/

hugie82

Everyone gave great advice but it depends on what you want to spend. Besides the obvious wheel choice, sway bar or bars would be second and shocks third. I wanted to throw my $.02 at shocks. I found the Koni Adjustable shocks cost about the same as other good shocks but you can dial them in for your set up. I was very impressed with the increased rebound setting. Whipping the car from side to side was much more controlled and it didn't give it a harsh ride at all.

NewbVetteGuy

This doesn't make any sense to me; I thought the purpose of a sway bar was to INCREASE grip in corners by allowing more of the tires to be in contact with the pavement and to have more of the weight distributed across more of the tires...

I thought the purpose of a sway bar is to INCREASE grip; how would it decrease grip?


Adam

Shark Racer

It's an impact of too much sway bar. The factory bars (7/16" diameter)are close to the limits of what you'd want on the rear suspension with a street car. The whole world changes when you're building a race car.

Honestly, your gymkhana, good tires and shocks, and an improved steering setup should feel very very good for a street car.

69427

Metalhead is correct.

You have to look at the force/grip curve of tires. If you increase the down force on a set of tires (say 20% for this discussion), you only get perhaps 18% more grip. Not a 1:1 relationship. During cornering (lets say it's a left hand turn, and we're discussing the rear sway bar) the body/frame obviously tries to lean towards the outside. This lean causes the outside/righthand framerail to drop, while the inside of the curve/lefthand framerail rises. This lean causes the right rear tire to rise up in the wheel well, effectively also causing the rear sway bar arm on the right side to rise, and rotating the sway bay. This rotation of the sway bar tries to cause the left rear tire to be lifted up by the sway bar left side arm, reducing the traction contribution of that left rear tire. The result is less traction on the rear, but more traction on the front because the front now has to do less of the work controlling body lean (and geometry changes).

Take a look at the old 911 racing Porsches. Unlike a front heavy Corvette, a 911 is rear heavy. They frequently had to run a damn stiff front bar to take some work off the rear suspension. The result was that at the cornering limit (maximum tendency for chassis lean) the big front bar was lifting the inside tire off the pavement. One tire doesn't have as much traction as two tires, so the Porsche would have fast corner understeer, a safe way to play it. If you put too big of a rear bar on a Corvette you get cornering limit oversteer. An underwear ruiner at best, extreme vehicle (and perhaps driver) damage at worst.

Real world example: Several years ago an acquaintance of mine had a bigass rear sway bar on his musclecar. His teenage kid took the car out for amusement one night. While driving like a typical teenager he got some snap oversteer while making a lane change passing another car. The car slid sideways/backwards into a tree, killing him.

If you're bumping up the rear bar size, do it slowly, and find a safe place to find out what the car does at maximum grip cornering.

NewbVetteGuy

I never had any doubt that he was right; I was only trying to express that I didn't understand it so that someone would give me the great explanations (and pictures) that have now been posted.

Thanks folks! -That picture really drives home the point, too.

Adam

fede

Yup, very good info. I also couldn't understand how a bigger sway bar would reduce grip!