Thanks, Bill.

 

I own three Corvettes, but that doesn't exclude me from recognizing the achievements of other brands, and how they are engineered.

I wonder why(maybe you can explain it, since you are a Corvette expert because you own one Corvette) why C5 and C6 owners, go with coil overs when they want to turn up the wick?

Maybe instead of you visiting Planet 9, Renlist and such forums, you should talk with LGMotorsports(who actually offers coilovers for the Corvette and actually RACES and builds Corvettes for racing).

 

I don't have the weight figures on the C7 but here are the numbers for a C6 Z06.

Stock OEM shocks(4) and springs(2) weigh 35.5 pounds.

LGMotorsports coilover shocks(including the included steel coil springs) weigh 30.5pounds.

The coil overs save 5 pounds(1.25 pounds per corner).

When GM designed the Sky and the Solstice, they went with coilovers to save weight and money vs composite leaf springs. Yes Shirley, GM has used coilovers on a production sports car.










Please explain how the coil over shock takes up more space around the wheel. Study the photos and you will see it doesn't.

 

Good article..

 

Thanks Joe.....Not sure how this relates to your Porsche luvin post but I appreciate your feedback. Adding coil overs to a Corvette doesn't change the type of suspension it has does it?

 

I was thinking the leaf spring arrangement is more linear and takes away the chance of coil spring bind and deflection? Am I barking up the right tree?

 

The spring doesn't change how the suspension works. The spring could be a transverse leaf spring, a coil over shock setup similar to the aftermarket ones available from LG and others, a coil over shock arrangement like GM used on almost every car they built from some time before the 1950s through the mid 1980s or it could be a torsion bar attached near the pivot point of the lower control arm like seen on GM trucks. The C2 and C3 Corvettes had coil over shock setups in the front of the car. The shock was placed inside the coil but the coil was attached to the A arms and not the shock.

I didn't say that manufacturers can't get a strut suspension to work well but they have to work around its problems. The Corvette suspension has performance advantages over struts but more than likely costs more as well. You don't see many purpose built race cars that use strut suspensions. Almost all of them use variations of the double wishbone design with maybe an extra link thrown in to counter some weaknesses and also some interesting spring and shock locations.

Here is a video showing the double wishbone suspension on an Indy Car and the main pieces of the suspension. Note where the spring and shock are located. The ME car could see something like this as there would be room to mount the springs and shocks in a similar manner.


Bill

 

The leaf spring has a unique feature of acting like a sway bar when mounted the way it has been on later Vettes including the C7.

This is that detail:

First, if the leaf spring were mounted in the center as it was on the C2-C4 rear end it basically acts as two independent springs.

However, Chevy got clever and copied the FIAT 128 that had the brilliant idea to mount the leaf spring at two points spaced far apart and let the spring move freely in the middle. This does something rather trick. It significantly increases the roll rate for a given ride rate.

Normally if you just had the normal ride springs on a car it still would run level. It will lean a lot more in corners but on the straights it will level out. That is the natural roll resistance (roll rate) of the ride springs. Normally this isn't good enough so a sway bar is added. Now when you push one wheel up the sway bar tries to pull the other wheel up. Net result less roll.

The trick thing that FIAT realized was the transverse leaf spring can be setup such that when the left side gets compressed, the right side "get's pulled up." Net result is it acts like a built in sway bar. See pic below.

An advantage of a coilover set up in a Vette when racing is spring rate can be changed for different tracks much easier and a wide variety of springs are available. Available leaf springs for Vettes are limited. (The set up I have on my street rod allows the coilover spring seats on all 4 corners to be adjusted so each tire load can be adjusted independently. The shocks are adjustable and it also incorporates a front and rear sway bar. All useful adjustments in addition to the many holes in the 4 bar link system for the best launch!)




By mounting the C7 leaf spring in two places, when one wheel is loaded in forms and "S" shape and also acts like a sway bar. May be one reason a rear sway bar is not used in the base C7.

 

Exactly the downside to the leaf spring is that it also transmits load across the car unlike a coil over and that it is more difficult and there are far fewer options to change spring rate.

 

Make a list.

In column 1) list all the current automobiles that use leaf springs.

In column )2 list all the current automobiles that use coil springs.

Which list is longer?

 

Joe,

The change I made makes a big difference. Suspension geometry and setup is truly an art form, and you've got to admit, stock Vettes handle pretty darn well. Change from stock to coil-overs, and you can make it better, but it's for sure not plug n play. I was talking to Lou Gigliotti one day at Cresson and asked him about what kind of shock I should get, single or dual adjustable.

"How much testing are you going to do?" I answered "Lou, I don't even know how to test". He told me to get '04 Z06 shocks. When I looked surprised, he said "if you get a 12 way adjustable shock, there's 11 ways to screw it up." So I went with the Z06 shocks. Were they better than my old Z51 shocks? You bet. Are there better solutions? Sure, but you've got to do the work to get the most out of them.

Have a good one,
Mike

 

For racing where you want total independent control of spring rates as well as tire loads at each corner and independent roll bar control, coil overs are preferred.

 

As an interesting aside. Before I sold my 2015 C7Z which was an FE6 car I was talking to Mike Levitas at DSC Sport about going to stiffer springs. Their Tractive shock bodies are already threaded for a spring perch but rather than removing the stock leaf and going full coilovers we were contemplating just using a light spring on the shock body to augment the factory leafs. You can order up lots of different spring rates to fit and that way you're not putting the full load on the shock mount that wasn't designed for it.

In the end we weren't sure if the spring would fit inside the control arms and I decided to just trade my car in for a 2017 with the Z07 package. However, it might be something worth considering for others.

 

GT2 RS is $300k, and anyone who pays attention knows Porsche are notorious for prepping the cars they use for laying down fast laps. Let's see how close the production car can get to those times with a qualified driver. The cheapest car ahead of the Z06 on the 'ring fast list is the viper, which is more than double the Z06 price.

I really wish GM would throw caution and price to the wind for an all out supercar effort, just to show they can.

 

Wait and see what the zr1 does. Still cheaper than the others, but it should annihilate some of these cars.

 

it will be very close to the vipers time, hopefully it edges it out considering the hp advantage.

 

OK, couple of mistakes in the various posts here.

To the OP's question, you can't really say struts are always worse than double A-arm. As others have mentioned there are some great handling cars with struts in the front.
A-arm vs multi-link. Well, A-arm is kinimatically a subset of multi-link. It just happens to have a number of the links meet such that they form an "A" and the outboard suspension joint of two pairs of the links (the upper pair and lower pair) are co-located. That said, multi-link gives you some suspension tuning options you don't get with a pure A-arm setup. Conversely, as used in the Corvette, the A-arm better ties into the box sections of the Corvette chassis. Multi-link almost always have some type of trailing link. Do keep in mind the C4 was a multi-link setup and the C2-3 could also be called a subset of multi-link.

Springs:
For the most part a spring is a spring is a spring. There was a comparison of the stock Corvette spring and shocks vs aftermarket parts. The aftermarket parts were lighter thus the poster incorrectly assumed that an OEM coil over setup would be lighter. No. First, OEM parts have cost and longevity standards (company internal) that the aftermarket doesn't have to comply with. So don't assume that just because an aftermarket company that doesn't have to worry about the their reliability reputation, will recommend a highly stressed spring type that GM could do the same.

Second, the comparison was for damper and spring. Well, if we are going to talk about the leaf spring then forget the damper. It only matters what the leaf vs coils weight. As a point of reference, when GM went to the C4 front leaf spring they said the weight savings was 1 leaf weighs 1/3 the pair of coils used in the C3. I'm sure the coils are better these days but that still a stark comparison.

This article and Cross Talk (ie marketing BS)
http://www.corvetteonline.com/tech-s...vers-vs-leafs/

Sadly, the author let Pfadt guy toss out the typical "cross talk" BS. The guy claimed that the leaf spring as used in the C5+ cars acts as a "Z-bar", the opposite of an anti-roll bar. That is just plain wrong. He was 100% wrong. In the Corvette the "cross-talk" is actually a good thing. All the "cross-talk" is, to an engineer, the ratio of roll rate vs spring rate for the given suspension setup. Even if you have NO anti-roll bar and coil springs in a Corvette you will still have a non-zero roll rate (ask a Formula Vee driver about a zero-roll rate suspension). The reason why we add anti-roll bars is because our standard ride springs are not stiff enough to give us the desired roll rate we want. Thus we add a spring that couples the left and right spring rates (ie the infamous cross talk). The "cross talk" is nothing more or less than the same thing people get when they add an anti-roll bar. Given a car with a leaf spring setup dialing the roll rate with a roll bar change is no harder than it would be with coil springs. It's just that you need a softer bar to begin with.

As has been mentioned before, the primary advantage to the leaf spring is weight (light and low in the car and allows for a smaller, lighter anti-roll bar). A secondary advantage is fatigue life (basically it will never sag simply due to age). The downside is cost, packaging (the spring must be able to span across the car) and failures due to corrosion/heat. I'm sure that cost pretty much rules the reasons why others don't use them much. Note that Volvo is once again using "Corvette-style" leaf springs in the rear suspension of their newest vehicles (when not equipped with air suspension).

 

The C2/C3 rear suspensions were very good for the time period and even now if you know your way around a suspension you can get them to handle. The C2/C3 used a trailing link to provide fore/aft location for the rear axles, the rear half shaft provided the upper in/out control along with the transverse spring and the strut rod that was used to adjust camber. Toe was adjusted by installing shims at the pivot point for the trailing arms. However, at extreme suspension depressions the design didn't provide enough. As the wheel dropped or raised in the wheel well it would move in an arc centered on the diff sideyokes.

The trailing arms had to twist in their pivot point to follow this arc which limited the suspension.



The C4 suspension was an improvement over the C2 suspension. The trailing arms were replaced by two trailing control arms which still had the same problems with following the arc the wheel followed as it went over bumps. A friend of mine went through the complete suspension of his 88 installing the stiffest bushings that could be found. When he was done there was no play in the suspension. After getting an alignment locally he decided to take the car to Bakeracing (Kim Baker) and have them do the alignment. I called that his $1300 alignment because they took out all of the modified parts and reinstalled stock parts because the suspension wouldn't work. I went with him to pick up the car and make the 3 hour drive home. The car handled fantastically. Kim explained they had to replace the trailing control arms because the stock bushings permitted sufficient sideways twist when the wheel went through its arc. My friend's choice of bushings kept the arms from pivoting sideways and bound the suspension when ever the car went over bumps because wheel travel was resisted.

The main difference over the C2/C3 suspension was adding a toe adjustment bar to control rear toe Vs using the trailing control arms to control toe. The pair of trailing control arms provided better control of the wheel than the single trailing arm of the C2/C3 but still had the disadvantage of the wheel arc.








That is where the C5 and on rear suspensions excel. The upper and lower control arms control fore/aft wheel position, in out wheel position and provide a larger range of motion for the wheel arc as the car goes over bumps.

Bill