geerookie

My intent is to start an open discussion about what is the best way to setup/design a suspension based on some preliminary fixed parameters. I'm using a C5 but I would assume most of this would apply to the standard C6?

1) Stock C5 control arm components and geometry
2) Either spherical/monoball or Delrin bushings on upper/lower and front/rear mounts (low/no stiction)
3) 3225# C5 with driver, fluids and 1/2 tank of gas
4) 51.5% front - 48.5% rear weight distribution
5) Tires are Slicks or R-compound
6) 300/660-18 front and rear
7) Coilover Springs and Dampers
8) Torsion Bar(s) (anti-roll bar) if needed using bearing/Delrin mounts
9) Car is used for road race type track use only. Not always racing and on many different track surfaces. Smooth, rough, slow corners, fast corners.

Through my research I have found that there are 2 basic schools of thought when it comes to suspension design.

BIG springs and soft/no torsion bars (anti-roll bar)

soft springs BIG torsion bars (anti-roll bar)

In the past I have leaned towards the soft spring BIG torsion bar camp. As I have been digging into this more I think I'm leaning the other way!

I'm getting ready to spend between $6k - $8k for a new suspension setup. The plan is Penske 8700 series 3-way adjustable dampers. I need to figure out dual or single rate springs, spring rates, torsion bars or not and if so what rates.

I have been running single adjustable coil-overs with T-1 rate bars and polyurethane bushings for 2 - 3 years now. It was much better than stock and served its purpose for those years.
I have been running 1:00.5 sec @ LimeRock, 59 sec @ Pocono North, 2:14.00ish @ Watkins Glen, I would like to improve those times by 2 - 3 seconds. I have a STOCK LS1 with 111k miles and I do not want to touch it. If and when it goes I will replace it with a stock LS6. I want to improve my times by improving the handling and the driver, not by adding horsepower.

A few things I learned....
1) Polyurethane bushings are a pain in the A%%, you have to relube them basically before every other track event if you want consistent performance and when you do 30 - 40 a year that is a lot of taking bushings in and out! Never again!

2) Coil-Overs make a HUGE difference in how a C5 handles/drives and feels, all for the positive

3) Single adjustable dampers are not enough once you move to the track and are serious about running quick times with consistency. Great for novice, intermediate and street.

So, my questions:

What is the best combination of springs and torsion bars (anti-roll bar) for the track? AND Why? Obviously, consider we don't get to run at the perfect track in the perfect world!

What are the differences on dampening curves and is there something considered the ideal curve? Is there an ideal Dampening to spring rate ratio?

What is the ideal ride height for the C5 considering, suspension geometry, aero downforce, and CG?

What is the BEST way to measure Ride Height?
Using the difference from the lower ball joint to the lower control arm pivot point like the factory says to do?
Or from the ground to the lower control arm pivot points or the frame rails.

JimbeauZ06

I know where the torsion bars are located on older generation P cars but not sure I've ever seen any on a Corvette.

geerookie

Not really where I wanted this thread to go but.......

What does a Corvette use?

waktasz

That's what I was thinking too. You mean swaybars right?

tjZ06

I also assume you meant sway bars. In some suspension designs (older P-cars, a lot of pickup trucks, etc) a torsion bar provides the spring-force in the suspension. In a C5 (or 6) Corvette a "transverse" leaf spring (running side to side, as opposed to front to back in a truck) provides the spring-force. It is clamped in the middle to the subframe, largely isolating any input from one wheel across to the other. Some "cross talk" is transmitted though via the spring material itself, since the center-clamp prevents any direct motion.

-TJ

John Shiels

anti-sway bars

geerookie

Not to start a pissing match, as this isn't really the point of this thread but an anti-(more correctly) roll bar is a torsion bar! It is a torsional helper spring that works when you are in a corner or when there are bumps in the road only on one side of the car and this could be a big reason not to use a torsion/ anti-Roll Bar on a very rough track!
I would call the torsion bars that are used on a trailer to help keep it steady anti-sway bars.

Tranverse leaf springs aren't even an issue as I have been and will be using coilovers.

sperkins

Lots of good reading here:

http://www.longacreracing.com/articles/art.asp?ARTID=30

geerookie

Thanks. That is one of many articles I have read.
Hence the reason for starting this thread. I want to see if anyone has better theory or advice before I invest the money.

worldsaway

http://farnorthracing.com/autocross_secrets.html
This is a good site for a complete discussion on set-up, and the guy had an '04 Z06

geerookie

Agreed, that is another great site which I have read through many times. Here's another one that has great info.
http://www.lemd.com/motorsport/class.cfm

I'm hoping to get people's personal insight or the reasoning behind the setup they run. I would also like some numbers for ride heights which are optimized for the C5. I know what the factory says and I know lowering the CG helps but I also know there is a point that the C5 will be the best it can be and a point where it turns to crap!

gkmccready

I don't think you're going to find a magic answer here. The spring rate you need front:rear can be different from the rate you need left:right. Anti-swaybars are a way of adding more rate for those lateral movements. You can typically generate more G loads cornering than accelerating or braking, and those loads need to rotate about the Cg of the car and the track is much less than the wheel base... seems like to control the lateral loads you need more spring rate than to control the longitudinal loads...

How you choose to achieve the total spring rate can differ. Big/Small, Med/Med, Small/Big. Throw in some aero where you need the springs to act since the bars can't and the game changes again.

When I was messing with coil springs I had recommendations from 425# front to 1000# spring, and rears from about 525# to 750#. Everybody seemed to assume T1/Hotchkis/Pfadt sized front bar (38mm?). And as you noted, the shocks need to be valved for the spring they're controlling.

In the end I learned that for the C5 or C6 asking this question turned out to be an opinion question. All the available set ups obviously work with the right driver in the seat, so really it's finding the set up that matches you as the driver...

geerookie

I hear you BUT.......

It seems to my feeble brain that there has to be a theoretical near perfect starting point for a "balanced" car. Then if enough adjustment is built in you can adjust for the various conditions on the track for that day.
I'm sure there are people out there MUCH smarter than me when it comes to the physics of a race car so my hope is they will pitch in.
I work in acoustics and when I design a system, the laws of acoustics define my perfect starting point and then from there I apply "technology/stuff" to adjust for the differences that I can't engineer out in the beginning.
So in my understanding of car dynamics I think we should be able to take a given suspension geometry, given weight, given CG, given tire and calculate the proper springs (in this case coilovers and maybe anti-roll bars) and dampers to work within the laws of physics.
From this we should get consistent ideal performance.
One of my assumptions is that you can calculate the "ideal" setup for a given vehicle taking all of these things into account. This doesn't mean it will "feel" good to the driver but it will use the laws of physics to maintain the maximum limits of adhesion. The limits are dynamic (due to track conditions) so that is where the adjustability comes into play.

Once you have a setup that is calculated to work at the limits then it is up to the driver to learn to drive it there
My hope is to learn from this thread what the right equipment and calculations are so I can have more money left to work on the driver If I don't have to buy things twice I save money even if it costs more up front.

Coil springs and anti-roll bars work together as a system. It seems to me that the anti-roll bar is a "patch" for a street car. If this is true then proper springs and dampers should eliminate the need for anti-roll bars on a track car or at least make the bars very small.

Any comments or enlightenment on the above is very welcome!

gkmccready

How many variables are in that equation, and how do you solve for them when the biggest variable is the nut behind the wheel and his/her interaction with the rest of the system?

I hear ya. I went through this. Spent a whole bunch of money. Got frustrated. Spent more. Got more frustrated. And got lucky in the end to find somebody that appears to like a car to behave the same way I do. Sometimes you'll get lucky and find that person (ie. setup) first, sometimes you won't. As I said in another thread -- if *I* could drive pristine configurations of all the vendors offerings back to back at the track then I could pick an appropriate one for me. Until then you have to be satisfied describing what you want and trying to find somebody that agrees and has it...

Again, if you want to control your body roll with spring rates you're going to have some pretty big spring rates. People just won't tolerate those rates, and on the track you may find that the rates to control the lateral motion are way too high to allow for proper longitudinal motion. So you need to use swaybars along with the springs to get your total spring rate right for both situations.

Also, remember, dampers control the rate of motion, not the total motion. You shouldn't be using shocks to control "total" body roll.

69427

The real world doesn't work that way. Race team engineers way smarter than you (or me) change the chassis setups at every different track. One suspension setup isn't ideal for all situations (fast or slow tracks, fast or slow corners, long or short straights, rough or smooth pavement, etc).
Unless you've got quite the personal automotive budget, most guys just find the best compromise combination of parts that works for them.

geerookie

There are a few components but they all should have fixed values.
Remember, I took the variable of the nut behind the wheel out!
That variable needs to learn how to drive the car after all else is calculated according to the laws of physics.
I'm trying to leave the "feel" part out of the equation. If the car is engineered to have max grip on a given course then it is up to me to learn how to drive it in order to extract that potential!

Kind of like a motor with 3000hp......at 850hp I might lose my nerve and lift off the throttle. Yes I went slower than I could have gone but the car was still capable of going faster. It was my seat of the pants "feel" that kept me from utilizing the full engineered potential of the motor. Now I could re-engineer the motor to have a different torque curve which reduced power to 2000hp and therefore it would "feel" better and then result in me holding my foot down longer and therefore go somewhat faster. But, if I just grew a set and learned to drive the 3000hp motor at it's engineered limit I would go faster yet.

My point is, I want to engineer an "as close to perfect" suspension within the parameters of the Corvette I own, in order to get the maximum grip and then, with practice I will learn to drive it.

geerookie

I agree that the design process is about compromise. Race engineers have a set of parameters "the rules" and the laws of physics to work within. They work in the "lab" to design the ideal setup for the given parameters then they go to the track and make tweaks to get the last 1/10 of a second out of it.
I want to design a package that extracts the calculated maximum traction on average track conditions and then with a range of adjustments I will be able to adapt to the changing conditions.
I think the engineering will get the car 90% of the way there, the tweaks may get another 5%. Then in order to take advantage of all that potential the driver needs to learn to drive it.

geerookie

To this point, Weight transfer will happen no matter what. Dampers, as you said, control the RATE at which it happens. You are right, if you try to stop it you will have massive springs and that will cause all kinds of bigger issues!

My understanding at this point is, you can't stop weight transfer and that is what people are trying to do with anti-roll bars! That is why when you see a car with anti-roll bars really cranking through a corner the inside wheel is usually off the ground! This looks really cool but there is no way that one front tire on the ground has more traction than 2 front tires on the ground. Therefore they are losing potential cornering speed.

Yes I realize, when this happens you have more weight transfer to the 1 tire left on the ground but I don't care how you do the math there is still WAY LESS traction possible! One tire getting 150% traction is still less than 2 equal size tires getting 95% traction each!

So as I understand it, the idea is to control the rate of transfer, so that it is complete at the exact time or just slightly after you start your next transition.
For example, when you turn into a corner the sprung weight starts to transfer/roll to the outside of the radius, the dampers should control the rate of transfer so that when you get to the apex of the corner you are near the limits of suspension travel but still have all 4 tires on the ground and are getting as much lateral traction as possible. Then as you unwind the wheel from the apex out, the weight transfers back to what is the inside of the radius, again at a controlled rate which ends when you are going straight.

If you want to control the amount of body roll you have to lower the over all sprung weight of the car.

Just whack me over the hear if I'm getting to far off course

69427

Only the uninformed are trying to stop weight transfer using bars. Weight transfer is just a fact of life.

You have to divide up the weight transfer/roll stiffness front to rear, and the bars are a useful and convenient way of doing that.

geerookie

I'm kind of confused on this statement??????
Weight transfer happens front/rear and side/side depending on whether you are brake/accel or turn left or right regardless. My understanding is the springs have nothing to do with this at all. The weight transfer will happen whether you have a spring or not.
The springs and dampers control the "roll" of the sprung weight. The anti roll bar is just a torsion spring that generally adds to the coil spring rate when the roll is side to side.
Did you mean something else?

How does the bar make it more convenient. Seems like it would make it harder to figure out the proper valving for the dampers as the rate will always bedifferent depending on how much body roll you have.