The difference you are feeling is the difference a higher quality shock and higher rate spring can make. You would feel the same thing with a set of hyperco leafs and penske shocks.

 

I'm sure I'd feel better performance from a lot of products. Anything has to be better than those leaf springs.

I'm convinced the GM leaf springs were transferring pitch from one side of the car to the other, translating to poor control especially in rapid succession tight turns. I remember hearing this from drivers at the track but never knew what I was missing until I did the upgrade myself.

 

I'll be ditching my leaf springs when I install my Eibach/Callaway coilovers. I won't be upgrading sway bars or anything else so I can give an objective review.

Mike (Bowmanized) has run the Eibach/Callaway coilovers with and without the leaf springs and he prefers without the leaf springs. I'd like to try both, but life is short and I don't want to have to install the coilovers twice just to come to the same conclusion.

Coil springs are cheap. Leaf springs are not. If you make a perfect choice with leaf springs you might be good. A mistake with coil springs costs very little to remedy.

On the issue of "crosstalk" with the leaf springs, I can't say yea or nea on that. I have read threads where most after perfomance junk the leaf springs. Almost all of the vendors here with coilovers do not recommend keeping the leaf springs.

The Corvette "stutter" over bumps in corners is unacceptable in any car, let alone a sports car. I'm hoping to divorce myself from this problem.

San

 

What do you mean by pitch? The leaf spring does act in part as an anti-roll bar. So if the car needed less roll resistance then removing the leaves and replacing them with same rate coils would give you softer roll resistance. Of course you can’t change out the leaves without changing the dampers as the factory dampers aren’t coil compatible. So again, do we know if the problem is the springs (which kinematic analysis doesn’t support) or is it a change in rates or the dampers that did the trick.


If you don’t change the swaybars you don’t have a straight A B comparison. I suspect half the aftermarket tuners don’t even really understand this. The leaf spring is both the ride spring and one of two anti-roll bars in parallel. So if you remove the leaf and substitute in coils of the same rate you now have a car that is softer in roll than it initially was. So that’s one change. You also have changed the dampers (change two) and perhaps the ride spring rate (change three – maybe). Ultimately the car may in fact handle better but that’s because a change in dampers, ride spring rate AND roll rate. With all those changes it really is hard to say what particular change did what.

You certainly are right that it’s expensive for an individual to guess and check leaves until you get the right one. Of course that isn’t a problem for GM. I think it’s safe to assume that leaf or coil, GM would be able to achieve both their desired spring and roll rates with either type.

The “crosstalk” is real. Not only is it real but it is a positive design attribute. There is a lot of confusion about how it works but it works well. Many people, including a misinformed Motor Trend editor, think the leaf would act like a seesaw and promote body roll. They couldn’t be more wrong. The leaf acts just like another anti-roll bar.

The Corvette stutter over bumps is more likely a combination of stiff springs compensating for OEM price point dampers.

Don’t get me wrong, as an upgrade coil overs can really help but the fundamental problem is NOT the use of a transverse leaf. At least one coil spring vendor, when pressed on the issue, admitted that coils allowed him to do a better job tuning the car but that the leaf is not a fundamental problem.

It may be very true that an aftermarket vendor can do a better, more cost effective job with coils. However, you should be very suspicious of any vendor who says the leaf is fundamentally or functionally flawed. That means they don’t understand how it works which also means they probably don’t know as much about tuning as they would like you to think.

 

When I talked to Mike (Bowmanized) he stated the Eibach/Callaway coilovers with the stock leaf springs were good, but removing the leaf springs and using a stiffer spring with the coilovers (to compensate for the lack of leaf springs) felt better.

I haven't seen most vendors condemning the leaf springs. I have seen that most say the car handles better with properly setup coilovers.

I really would like to try the Eibach/Callaway coilovers with the "weak" springs and leaf springs and the "stronger" springs without the leaf springs for comparison purposes, but time is money and I just don't have the time or patience. I also put a substantial amount of credence in Mike's opinion.

I'm not here to defend or criticize the leaf springs, and it seems to be a touchy subject. When you're driving down the street, no one knows if you have leaf springs or not, they just know it's a Corvette.

San

 

This is a great discussion so let me shed some light on my suspension philosophy and try to clear up any misconceptions about the 'bowmanized' setups.

Stock suspension whether it be C6 or C6Z are a compromise for streetability and performance. None of them are designed for all out performance. GM has to sell these to the masses and if they put huge spring rates on their cars they couldn't sell as many as the suspension would be too harsh.

Sway bars are really designed to add performance to street cars that don't use spring rates that are track ready. So they add roll resistance without using harsh spring rates.

My suspension philosophy is based on increasing spring rates and shock rates over stock to provide better roll resistance, as well as better braking and accelerating weight transfer resistance. If you use stock leafs, shocks, and huge sway bars you'll have good roll resistance during mid corner but the transitions won't be as good and either will the braking.

The shocks are the most important part of the suspension that San purchased. These are a DeCarbon shock package. Nitrogen charged shocks made of aluminum. The remote cannister keeps the shocks from cavitating and also helps them stay cooler. Also as an added bonus you can adjust the shock compression from the cannister.

Every track is different and you have to have adjustable compression in order to get that last 10th IMHO. As you tune the suspension you accomodate for grip levels. You also can tune for high speed turns or slow speed turns. Driving an autocross course on run flats and racing a corvette at Le Mans or Miller Motorsports park would require much different shock compression. The rebound isn't quite as crucial for performance. You want the rebound set for the spring rates however and when you change your spring rates you want to be able to change the rebound.

Also Callaway has the $$$ to spend on research. This was over a year long project with Eibach. Numerous times Eibach had shock rates and Callaway Engineers would come out and give feedback for changing the rates and behavior of the coilovers. Another advantage of these shocks is durability. Some of the other high end shocks that have similar features will need to be rebuilt far more often since they're designed for race cars not street cars.

High speed compression is critical to the Corvette handling at the track. Often times you'll hit bumps and curbs at the track while you're already cornering at over 1G and you need ample high speed compression. This HSC is the biggest flaw I see with most of the shocks out there as this is the first item compromised for 'streetability'.

Keeping the tires in contact with the road is the most important part of suspension. Precisely why I use increased spring rates and street sway bars. I do like sway bars for their adjustability but NOT for adding wheel rate. I don't like how big huge sway bars lift up on the inside wheel when cornering. I've seen some cars at the track 'Up on 3' and that isn't the fastest way around.

So we use increased spring rates to help control the body roll, dive, and squat without neccessitating large sway bars. However if you have bigger sway bars already we can accomodate that by lessening the spring rates. Also we can effect the overall handling by selecting the rates for your car. If you want more oversteer or understeer you add rate accordingly.

The advantage of the coilover springs is adjustability. If you want to change it's relatively inexpensive just like San mentioned. Also the coils are lighter. I weighed the C6 Base leafs, bolts and mount at 22lbs and the coils are 8lbs. 14lbs is 14lbs. Another advantage is they're easier to ride height adjust.

The idea that the leaf adds roll stiffness is definitely true but at the same time it's also pulling up on the inside wheel. I really don't see this as an advantage or disadvantage. Rather it really makes the sway bars seem bigger.

BTW Both Callaway and Eibach are completely aware of what we are doing here at bowmanized by offering another tremendous suspension package. They are thrilled of the results so far and appreciate my expertise with spring rates and ability to adjust the shocks.

I do like the coil springs better there is no question. However I also think that you can make your suspension just as good with leaf springs. It's just a lot easier to do with a coilover. In fact, now that I know the coilovers have record setting capabilities I was considering getting Hyperco leaf springs to use in conjuction with the Callaway Eibach coilovers and 'additive' spring rates just to prove their design works. At the end of the day the double adjustable, de carbon, aluminum, remote resevoir shock is the most important part and not the type of spring. The spring RATE is much more important than the type of spring. The Eibach Springs are the best on the market and 100% made in the USA, and so are the shocks.

 

Thanks for chiming in Mike. I hope I didn't misrepresent any of our conversations.

San

 

I do not track my car. What I do is very spirited driving through coastal and mountain "twisties."

Prior to my suspension upgrades I had to fight the car in fast turns, "roll" or "pitching." I also would experience wheel hop in turns that had a few bumps, especially accelerating when coming out of the turn. Loss of traction was extremely irritating and not how I wanted a Corvette to perform.

Since loosing the leaf springs and installing the coilovers/bushings these issues are no longer even present. It's like the car is on rails now, and the wheels grab at all times, no skipping or hopping. It's utterly amazing how much a difference it is.

Even though I am using a different brand, I concur with Mike that the ride height is easily adjusted lowering the gravity center a bit which IMO is a benefit as well, and because the spring rate is adjustable I am having fun finding that sweet-spot between street and performance compatibility.

 

I agree with everything you said buddy, and I am looking forward to hearing your feedback. Especially considering you've tracked AWD cars with coilovers, I really think you'll have a broad basis for comparison.

 

I think it would be safe to say loosing the leaf springs AND the OEM bushings AND the OEM dampers you prefer the handling of the car.

Mike had a very good post. I do not want to put words in his mouth but it does seem he agrees that there is no inherent problem with the OEM leaf spring and that the reason to go to change it is to achieve a change in spring rates, not because the base spring is mechanically deficient. It also seems that he agrees with another vendor I talked with in that it is cheaper for an aftermarket vendor to achieve a spring-damper-roll bar combination with coils as opposed to the leaf.

Again, the car certainly may feel better after changing out all these parts but that doesn't mean the leaf spring is a flawed concept. It means you prefer a different damper-spring rate-roll rate combination than the factory provided.

 

So, what I'm getting from this discussion is that I don't need to spend a ton of money to "upgrade" my base suspension with coilovers, new sways etc. Just some new shocks and poly bushings would make a big difference for autox and street use.

 

You should upgrade the sway bars too. Z51 sway bars are a good bang for the buck. They will work well with new shocks and poly bushings.

 

The answer is a definite... maybe. How's that for ducking the question.

Actually, I'm not trying to play politician. However, the answer isn't as simple as that. Certainly better dampers will make a huge difference. However, it is possible you will also want stiffer springs. If you do then the leaf spring has to go. You can either replace it with a stiffer leaf spring or with coils. However, if you or the person engineering your suspension upgrade decides the factory spring and roll rates are spot on, then no you would not benefit by going with coils. However it is quite possible you would want to use both better dampers and stiffer springs.

As Mike said above, he uses stiffer rate springs with the Corvette. It sounds to me like he maintains about the same roll stiffness as the factory by removing the leaf (which would effectively soften the roll stiffness) but using stiffer ride spring rates. Because the ride springs do contribute to the car's overall roll stiffness Mike's changes probably result in better shocks, stiffer rate in bump but similar to factory rate in roll. Of course I am entirely speculating at this point. Mike could likely give you a better answer.

Of course another alternative is to use the helper spring concept. As an upgrade I can't see anything theoretically wrong with it but I can not say if it works better in practice. A theoretically good idea poorly executed often will be inferior to a poor idea executed well.

 

I told myself not to get into this on the C6 tech.

Randy

 

Thanks for the info. What do you consider better dampers? Would Bilstein or Koni do the trick?

 

Might look at this thread:

http://forums.corvetteforum.com/show....php?t=2038220

 

Your buddies have been watching too much "TOP GEAR" Those guys use the same exact comparision about the corvette using leaf springs. They really bash vettes bad on that show. After one of the guys actually drives the car he admitted to the other host that they really "work". And I think this was a base c6 non zo6 or z51.

 

Guess you missed Clarkson's review of the Z06 which is a corvette last time I looked. One of my favorite shows. They say outrageous stuff on the show all in the name of entertainment. And they bash anything that deserves it. Did you see the review of the Countach?

 

send you friends my way I'll show them what a leaf acn do.