There is no 600lb Z51 spring. The 84 Z51 spring was 582, but it won't fit in my later car. For the later C4s, the only front spring close to that rating was the 660lb Challenge spring. I have one of those, and it works pretty well (someone else is borrowing it to autocross in his C4 right now) with a commensurately lower-rate rear spring. It's not the night-and-day difference you describe.

However, it's an apples:oranges comparison between front springs for an early C4 vs a late C4. My front spring is 1125lb. But as we've already discussed, the 88-96 Corvettes have a considerably lower motion ratio than the early C4s, and lower than the MR for the shock mount also. The MR on a later C4, at least with the VBP Xtreme spring I have (the pad center on it may be located in a slightly different spot than the stock springs), is 0.55:1. The shock mount's MR is 0.76:1. So a 600lb front monoleaf in my car would have a lot lower wheel rate than one in your car: only 182lb. And it would also provide a lower rate than a 600lb coilover in my car. In fact, my 1125lb front spring creates a wheel rate of only 340lb/in, slightly lower than the 347lb/in wheel rate provided by a 600lb coilover on my car. A 1125lb front leaf in your early C4 would provide a much higher wheel rate. In fact, it would ride about the same as your car with an 1125lb coilover spring.

*The above paragraph was edited to reflect actual motion ratios for my car, as measured by the previous owner. I just found that info.

Can you please provide the following info about your pre-coilover setup:

• Exactly what leaf spring was in the front of your car?
• What shocks were on the front of your car when you had the leaf spring?
• What are the differences in compressed length between the old and new shocks, including bump stops?
• How does your ride height compare before and after?

 

There is some learning that can occur in this thread, Blackozvette, if you can spare the time. I'm looking/listening.....

 

Fact - I stated it was my personal experience and opinion that a 600 lb coil was more efficient than a 600 lb leaf in the front of the C4.
(and lets not split hairs over the leaf 600 lb rate, early springs slightly less, later ones slightly more)

Fact - I stated that an upright coil was more efficient than the lateral leaf (again my opinion based on the above) I did not state the leaf was inherently inefficient due to the fact it is lateral. Matthew made a comment about a spring being a spring being a spring and its rates remain constant. My reply was if you begin to lay a coil over it loses its rate and its not the same spring anymore (I used this as an example) this then turned into an attack by Matthew and Tom who have both decided to go off on their own little tangent about how wrong I am about leaf springs.

Fact - my experience and opinions are based on converting my C4 to coilovers (both front and rear) and going racing with them. Perhaps Matthew and Tom could do the same and then get back to us with their 'experiences' on the subject.


I can happily accept that people wont always agree with anyones (including my) point of view. Quotes like this are make it quite clear that you do not value anyones opinion or experience if it differs from your own beliefs on the subject.

The tag team tactics of Matthew and Tom are nothing short of online bullying, but it has been going on in CF/C4 for quite a while now, and it does nothing to promote any healthy conversation on any topic - I have seen many people suffer from tirades against them like this thread has produced. Its a damn shame really.

 

You didn't state it as an opinion, you stated it as a fact. The problem here is that "efficient" is not a term that has any applicability to a spring. Springs are not more or less efficient than one another: they always store and/or release 100% of the energy put into them. All of my posts on this thread have been asking you to clarify what you actually mean by "efficient" springs. AFAICT, what you really mean is that one form of spring results in a different wheel rate than another. But this isn't true. The reason a leaf spring may result in a different wheel rate than a coilover has to do with the motion ratios of each, which is a result of control arm geometry rather than anything inherent to the spring's form. FACT: if a leaf spring's ends and a coil spring's perch exert the spring forces on the same control arm location, they will both produce the same wheel rate for the same spring rate.

Nobody attacked you. In fact, I've asked you to clarify that statement because I couldn't understand what you were talking about. If you were talking about laying a coil spring over, then obviously that changes the wheel rate. I'm not sure how that's germane to the discussion, though. You're muddying up the water by conflating spring rates and "efficiency" with suspension geometry. When I say "a spring is a spring is a spring," what I'm pointing out is that all springs do the same thing regardless of their form (coil, leaf, torsion, etc.). And a spring rate means the same thing for any spring, regardless of form. IOW, there is nothing inherently better/worse or efficient/inefficient about one spring vs another.

We all understand that this is based on your experiences. However, the problem is that you changed quite a number of things, any/all of which could have major effects on handling and lap times, but you've attributed 100% of the improvement to the form of the springs. That's a classic logical error: discounting confounding variables. I made a bullet-pointed list of potential variables, and asked you to provide the info on each so that we could better understand all the factors that may have changed your car's handling, but you haven't been willing to share any of it, including what actual leaf spring you even had in your car. If Tom or I converted our cars to coilovers, we'd have the same set of confounding variables.

The best way to do this would be to start with an adjustable-height front leaf, like I have. Then one could install the actual coilover dampers without the springs, and start by dialing in the damping rates. Then, and only then, one could remove the leafs and install coils that provide the same wheel rate (in my case a it looks like a 600lb coil is very close), adjust to exactly the same ride height while leaving the damping adjustments where they were with the leaf, add however much swaybar rate is lost when the leaf is removed, and check for any differences. That is the only way I can think of to eliminate the other variables. The time and money involved in such a test is considerable, but if you're willing to fund all of that, then I'm willing to try it. But we really don't need to test all of this. It's well known and established how springs and motion ratios work. And it's not like I'm dreaming this tech info up: I've learned this info from actual engineers who design suspensions and/or good coilover kits for a living, some of which are at the highest levels of motorsports.

The thing is, the way springs and control arms work isn't a matter of opinion or point of view. It's purely a matter of fact. I value people's opinions and experience very much, but when someone states something as fact that isn't accurate, I won't accept that. I'd love to learn more about your actual experiences with all of this, which is why I asked you to clarify a bunch of details about your before/after setups. It's not too late to provide that info, so that we can all learn.

Again, there's no attacking, bullying, or tirading going on here from either Tom or me. We are only discussing facts about simple physics. Again, what you did was to state certain things as facts, and your assertions fly in the face of basic physics. All I've done is point out where your assertions conflict with what is well known about springs and suspension geometry. I've been really polite about it, too - I was truly interested in having the discussion so we could all learn. For example, I learned that early and late C4s have really different motion ratio geometry; and I was inspired to go find the actual measured motion ratios of my personal C4, which I didn't know before. But if you expect everyone to just accept your erroneous assertions as fact, and you get your feelings hurt when someone points out facts that contradict them, then none of us learn anything and some of us will learn wrong things. That's not helpful for anyone. I sincerely hope you'll change your own point of view on all of this, and rejoin the discussion by answering some of the questions I asked.

 

I think I can see what is going on here. I think that this "discussion" was over before it began. Blackoz feels attacked and has moved to defensiveness. That's unfortunate...I'm all ears on this topic, but I want to discuss it using real facts, math and data...not "facts" like this...
...and this as a mind set:
^Trying to discuss this with science/math/data. Why didn't you just answer the questions Matthew asked you? I believe that he was simply exploring the reasons why you had the observations that you had. I'm interested in this too.



You've made some pretty hefty assumptions here....IDK why. *I* value opinions and experience...I value that, combined with science a whole lot more. So let's combine the two. That's where I thought this thread WAS headed. Tom and Matthew aren't "ganging up", we aren't bullying or anything like that. Tom and Matthew don't even know each other (other than that he's a member on here). I can't speak for him, but I believe that we're both exploring things until we have a full and complete understanding of it's function. That requires open, honest communication. Unfortunately, some people perceive "open/honest" as an attack. Leesvet quit the forums b/c I told him that the fuel pump runs during cranking. . That's not attacking, ganging up, or bullying...that's fact. I'm sorry that you felt accosted by my participation in this thread...that wasn't my intent at all. Happy holidays.

 

with this.

Over the years, and on all C4^ forums, you see thread after thread where people recommend going to coil overs to improve ride and/or handling. Repeatedly, this recommendation is backed up by the assertion that "I changed to coil overs and (ride and/or handling) was way better". Well what actually happened in that case? Did the coil spring improve the ride and/or handling? In most cases, the person posting changed old worn $89 Bilsteins with new adjustable ~$200 shocks, possibly changed their spring rate, and definitely changed their MR. Had they simply put the new, adjustable ~$200 QA1's (or whatever brand came with the coil over kit) on their car, they'd have likely realized the same or similar benefits. So misinformation is likely being passed on; "Coil overs are way better". Matthew is right that most don't change just the shock...then later, the springs and that is for time/cost reasons...and most also have no good way to measure changes. SOTP is about it.

Eventually, I'll be putting "coil over quality" shocks on my Kart project, but retaining the monoleaf springs. Unfortunately, I have no objective way to measure the improvement of the shock, and likely won't even continue with a change to c/o's due to cost. But I MAY, if it could be proven to me that there is an objective/actual benefit....which is why I'm "IN" on this conversation.


.

 

I find it interesting to argue against coil overs. If you have the adjustable flat front spring maybe there is advantage. Production style it's bolt it and deal with it, not really adjustable. The ride height is what it is. Adjustability is the advantage of coil overs. Spring change 20 minutes. The ability to reset ride height and corner weights quickly.

 

Yep, so with an adjustable-height leaf like my VBP Xtreme, it has easy adjustment for ride height and corner weights like any adjustable coilover. However, the real problem for now is that no such spring is currently in production. This may change in the future - I've been told someone well connected to the Corvette aftermarket that another company is tooling up to make them. But who knows?

If - big "if" - an adjustable leaf spring is available, then the big advantage to coilovers is the easy swapping of front springs for different rates, as well as the availability of a wide range of spring rates. Aftermarket stiff leafs are easier to change out than stock leafs (they have less curve in them, but the fronts are still a bit of a pain. In the rear, the leaf spring is quick and easy to swap, and it's easy to make it adjustable for ride height and preload, so they are probably a wash.

 

On my 89 Autocross car, My front "Production Style" 1470 pound monoleaf spring is totally adjustable and it only takes a few minutes to adjust the corner weight. It takes me longer to setup my platform and laser level it, put the car on the scales, air the tires to race trim, disconnect the sway bar, put the driver's weight in the car, than adjust the 4 corners to 50% cross, 50.2 front & 49.8 rear.

 

Since, VBP is now history, it is my understanding that Van Steel has a source for the extreme rate adjustable composite springs. I hope that is true and they are of a good quality. A friend of mine converted to coil overs in the front and will eventually have the upper mount beefed up when he can get his car to Mike Maier, Inc. to rework the mount for reliability. He is using 1,000 pound springs on each side with his Tripe Adjustable Penske Shocks. At first, I thought the 1,000 pound spring was way too much but, it appears that it may be the right rate. The only reason why he went to the coil overs is because he could not get a heavier spring than a 1200 pound spring.

 

Matt:

Any chance that you can talk Chris Ramey into posting a picture of his rear coil over shock mounts he fabricated to beef up the lower mounting point?

 

Did you add adjustable bolt? I'm running FHB front with cut down pads (3/16) and small 1/8" spring tips.i cut down aluminum brackets there are no shims I think still think its a little high up front. It still required 1 lower control arm to be removed to install. Granted it was much easier than a FHA

 

The custom made spring came with the hole pre-drilled with the adjusting screw mount, and the adjusting screw with, which I believe is about 2 1/2" to 3" in diameter and about 2" tall very hard rubber at the bottom of the adjusting screw.

This is the top of a 1222 pound spring I have as a spare:



This is the bottom of the spring.

 

This is what a 3,000 pound 89 Corvette looks like with a 1470 front spring, 837 pound rear spring and I have a 6-point cage, making a very hard turn.

 

See below. He posted this on Facebook a while back, so it's in the public domain. He cut the stock shock mount portion of the aluminum upright/knuckle casting off. Then he used this fabbed steel bracket in place of it. As you can see, it bolts to the two trailing arm mount holes, as well as the camber rod hole. This is the only view I have, so I don't know what the other side looks like. But it appears to move the lower shock mount quite a bit inward, such that the coilover looks like it's vertical or nearly so. He said this was version 1, and they made some sort of improvements to it for a v2. I don't know what those improvements were.

 

Thanks Matt. I really appreciate it.

 

I'd like to comment on this, because it's a great point. Why argue against coil overs? I don't think that I have done that specifically, although I can see how it would appear that way.

For me, I'm all about $$$. Coil overs cost a lot. Good shocks, combined with a monoleaf costs a lot less. If we all had so much money that money didn't matter then the case for Coil overs would be more clear.

The second thing is the actual realized benefits; What is their REAL benefit? Easy (front) spring swapping -the rear monoleaf is actually easier and faster to swap, IMO. How many of us on the CF forums are swapping front springs for events/conditions? Not many. How many forum members care about or need to care about corner weighting? Not many. Probably 99% of coil-over swappers don't change their springs, corner weights or ever touch their pre-load adjusters once they've set their desired ride height (usually driven by "looks"). So they could have accomplished the same thing with stock springs, ~the same amount of labor, and less money.

Finally, misinformation. As I stated earlier, you see post after post where someone swapped to coil overs and fixed some ride/handling issue. The shock fixed the issue, not the spring. So now folks read that and think they need coil overs and the requisite mods to install them, for a basic maintenance problem; crappy shocks. I've been a victim of this very problem on the very forum -you don't know, someone says something and you believe 'em. You spend a bunch of money and then 1. convince yourself that something's better, or 2. your unhappy with the value of the change. I think a lot of people have it stuck in their heads that "leafs suck" and coil overs are the answer/fix. And why not? Car mags and other publications erroneously pick on the leaf spring design and frame it in the same light as the leaf springs on a pick up truck...or a horse drawn cart. This leads people to eliminate the leaf, for reasoning that doesn't exist, I believe.

For not a lot of effort and for basically $0.00, you can mod the stock front spring so that you can adjust ride height and corner weights and then the only down side compared to a coil over (that I can see) is rate tune-ability. Especially for the average forum member.

 

Coil overs arn't IMO for the average C4 Corvette owner. The benefit of coil overs is in the front, not so much the rear. If you track your car at the same track week in an week out once set up is set you are just tweaking. If you run multiple tracks you may different springs and shocks or settings. Most owners aren't opting for high rate springs or even adjustable shocks. The beginning of the thread related to the high cost of aftermarket performance springs made coil overs comparable in cost. Notice he didn't price a kit but the pieces to build his own.

 

Spot on, the only reason I went to coilovers was simply the cost difference. I needed a new front spring as mine was cracking. So I either had to buy a new front spring or go to coilovers which is springs and shocks. With making my own mount/using QA1's cheap ones I was able to keep the cost pretty low. If someone simply wanted to go to coilovers with no current issues with their suspension it's definitely not worth it unless they are track monsters. Yes coilover's present more options down the road. Yes they are generally easier to adjust/change. But, the average Joe isn't pushing their car to need those capabilities. Am I happy with the switch? Yes. If I didn't need a new front spring at that time, would I have switched? Probably not.

This thread has turned into quite the debate! I'm all for a good discussion but it is difficult for any readers of this thread to distinguish between the objective and the subjective information. There are a ton of different person experiences from different setup but generally they are never narrowed down to one variable. Most of the time when a major suspension change like coilovers occurs the vehicle now has new shocks, a new alignment, possible different ride height, etc... If anyone would like a very technical textbook on these topics, I highly recommend "Fundamentals of Vehicle Dynamics" by Thomas Gillespie. You can pick it up pretty cheap used on Amazon or Barnes and Noble. Vehicle Dynamics theory in the book is reality. It's a very physics based environment. It becomes difficult to represent every single variable in a system to completely estimate how it reacts (think ball joint stiffness, bushing stiffness, wheel stiffness, etc... some of which aren't exactly linear) but estimations are extremely close. This is how modern vehicle suspensions are designed, around proven theories and principles. Just remember that it is very rare for only one variable in a system to change for us to truly understand what made the difference that we feel/experience.

 

1. Jack the front end up and secure the vehicle on suitable large jack stands from the frame on both sides.
2. Remove the front skid plate from vehicle.

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