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Discussion Starter #1
DJ etal,

What do you guys think about the coilover conversions for road racing rules and sactioning bodies aside? IMO I do not think much of them. 1) the stock spring has less outboard weight and better contribution to center of gravity. 2) coilovers put stress into the tub in an area never designed for this purpose. 3) assuming springs of all types and design are to control wheel rate and assuming that with the stock design movement on one wheel does not instantly effect the other wheel like a roll bar I see no advantage to the coil over conversion. 4) makers of the conversion to my knowledge do nothing to strengthen the top shock mount area from flexing and you now need to strengthen this area and add more weight in strut tower bars or roll cage tie in to fortify this area. Any other opinions besides the C5R does it so it must be good??
 

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I only recommend them for dedicated tracked cars.

There are defininte tuning advantages in that
- ride height and corner weight are now independant variables,
- there is an infinite selection of spring rates
- spring rates can be changed quicker
- spring rates are independant on each corner as are corner weights.

Your assumptions are incorrect:

- There is "cross talk" from side to side across a leaf spring both mechanically and harmonically
- The coilover springs are lighter, your just comparing the springs not the whole coilover unit (including shock). There are in fact Titanium coil springs availble which will drop the spring weight 40% more.
- Note that the coilovers should be mounted on inverted tube monotube racing shocks. These shocks are lighter and have a much better unsprung weight (nil). These shocks can be built with shorter bodies and shafts which accomodate shorter springs. Thus allowing the car to be maximally lowered. This lowers the CG and Roll Center.
- Lighter weight spring rates can be used as you are multiplying the spring rate by the angle coefficient. ='s Better response.

I recommend, as does Chuck Mallett, that the upper shock mounts be reinforced. There are brackets availble for this.

Coilovers will improve the handling if set up properly. There is some testing involved.
 

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Discussion Starter #3
DJ,

I am collecting parts and learning info from you for a totally dedicated track car. Thanks for the info. By late next year my old race car is out and the Z is in as a non-sanctioned club racer. So rules per say are not an issue. But to me I prefer a car that handles more than I want Horsepower. I'm spending this year learning the car and slowly building it before I race it. I'm into full proper cages, gutted interiors, full containment seats, HANS, heimjoints etc.. I know nothing about Vettes so I appreciate your input. Since there is crosstalk with the leaf spring I understand you 100% and my initial premises are then faulty. Do you know who makes the upper shock reinforcements? I did a quick search and found no one who makes them. How about LG? I did not see shock mount reinforcement as part of their coil over kit.
 

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The shock upper bracket reinforcement is used by some but not all. I recommend it.

It can be as simple as seam welding the bracket to the frame and/or adding a reinforcement plate or gussetts. Most are custom fabbed.

Some aftermarket race suppliers have these such as Pegasus or Hoerr Racing Products. They may or may not be specific to the C5.

Note that the suspension loads are normally transferred through the AArm mounts and the upper shock mount anyways. The leaf spring center mount only acts as a pivot point (theoretically). Installing coilovers does not transfer this load to the frame any differently as the upper shock mount and upper AArm mounts are all in the same vicinity. It is just that with coilovers the upper shock mount may be carrying more of the same load.
 

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Discussion Starter #5
DJ wrote: "Note that the suspension loads are normally transferred through the AArm mounts and the upper shock mount anyways. snip... It is just that with coilovers the upper shock mount may be carrying more of the same load."

Agreed. Just because the coilover upper spring perch is there new load into the upper shock mount area results as I see it. So I think that reinforcment in this area is required especially because GM never designed this area to handle the extra load. Additionally, roll cage tie into this area is essential. Perhaps others who do not reinforce this area think that rollgage "tie in" is enough.
 

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Could somebody please tell me why GM still uses leaf springs on the Corvette? The first time I realized this, I was shocked.

Bob
 

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Discussion Starter #7
Bob I was surprised too because I bough my car on reputation and constant hazzing by Z06's on the race track. I really did not even know where the gass cap was when I bought the thing. Don't confuse the leaf spring of old rear suspension truck design with the transverse leaf to support the independant A-arms. It is acutually a very clever design. I am very reluctant to change it. However, with more research I am sure DJ's explaination of "crosstalk" between the left and right of the leaf will pan out. Coil overs make the suspension truely independant (except for the rollbar). What I am not sure about (and maybe DJ can answer) is...If we can live with the action/influence a sway bar has on the suspension left to right, then why is the leaf spring crosstalk important? The talk would be some amount less than the swaybar and make a linear contribution to it I would imagine. Most of us clubracers are not really skilled enough or test enough or have a good enough ass-ometer driving a 3000lb car to swap out coilover springs for lower laptimes for the specific tracks we run. So unless you are the type who can feel what happens with different springs you probably will take a set-it and forget-it attitude. That means once you got the leaf spring you are happy with, coil overs offer no advantage. In fact we all know tires makes perhaps the biggest difference in racing and 95% of us club guys use our slicks too long and go too many heat cycles and loose more performance perhaps than the difference between leaf vs coilover. But as a gadget guy I vote for coilovers and will 95% chance put them on my car. DJ...comments?
 

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To maybe help you research
"If I were involved in the design of a new passenger vehicle, however, I would give serious consideration to the use of a transverse composite single leaf spring of unidirectional glass or carbon filament in an epoxy matrix [fiberglass or carbon fiber, my words]. This would be the lightest practical spring configuration and, although space constraints would seem to limit its use in racing, it should be perfectly feasible on road-going vehicles, from large trucks to small commuter cars. (Since I wrote this paragraph the new-generation Corvette has come out with just such a spring to control its independent suspension systems-at both end of the car.)"
Engineer to Win, Carroll Smtih

Carroll Smith was team manger for the GT40 at LeMans, and has written several good books for the racer and racecar engineer. http://www.motorsport.com/news/article.asp?ID=124174&FS=SAE

My point is that the composite transverse leaf springs are the lightest suspension setup for those who have the space (i.e. road cars). And Carroll as well as the engineers at GM seem to agree. I remember reading the GM claims about 20-30lbs weight saving per spring = ~100lbs.
I say this because I am tired of people ridiculing the design especially when they dont know what they are talking about. :mad:
If you want to ridicule subpar designs on sports cars: Porsche, I'm looking right at your macpherson struts. :NoNo:

ok I'm done ranting. :eek::
Drew
 

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Discussion Starter #9
Drew,

While the concepts of the transverse leaf spring (TLS)may be true...in racing there are other issues. For example, I do not do this but, some peopel use dissimilar springs at the 4 corners of the car on a coilover suspension to tune for different tracks. To may knowledge there is no predictable way to do that with the TLS. On the surface the TLS has many advantages. Also don't forget that GM will make dscisions on cost too. So don't think GM does something just for our performance benefit or the whole body of the car would be carbon fiber. It is all about cost benefit and sometimes it is not to your benefit. But true I am very intrigued by the TLS and I will need more research to decide how to handle it. Personally I like the simple design and my car handles great just the way GM intended. As you race a car you start to find weak spots. You modify these weak spots out then you get new weak spots. That's racin...
 

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Maybe I didnt explain clearly, but I totally agree/understand that composite transverse leafsprings are not ideal for most racing efforts. Even though there are ways to consistently achieve different spring rates at different corners with the TLS, the process is somewhat involved and would require computer/computational tools that the typical racer doesnt have available. Suspension coilovers are a first choice for race efforts for good reason (some of which you mentioned). Other reasons is that its easier to design (in my opinion) mechanical rising rate springs with coil overs, as well as the better packageing bonus.
I was just trying to point out that the TLS has many advantages for production cars, even sportscars. One of the big advantages I see it that it allows that rising rate of the spring to be decoupled from the damper. This really allows for better damper tuning. As you already know, the damper is velocity dependent and the spring is position dependent, coupling them together in a coilover really makes it more of a compromise when developing the setup.
I am disappointed by the way many people dismiss the TLS idea without really understanding it.
I think its related to the way some people will say "Ferrari/Porsche/C5R/Formula-1 does it this way so it MUST be the best way to do it." :roll: Without considering thier particular design paramters, and understanding what thier particular design needs, the assumptions are ridiculous.

"...the whole body of the car would be carbon fiber."
thats not true, kevlar would be used for all non-stressed components, like ducting. Its lighter than CF you know. And would be used for all impact aborsbtion areas (since it has a larger strain percent to failure than CF).


But yeah, every design is a compromise, including cost compromises.
Drew

PS: Good luck with your efforts in modding and tracking.
And remember, the quickest way to a small fortune in racing is to to start with a large one.
 

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Im really surprised a coil over system would be lighter than a composite leaf spring+shock setup, especially considering that only 30% of the plastic leaf springs weight is on the control arm since 30% is mounted in the middle of the chassis. As far as tower pressure points i would think that the fact that the stock shock being mounted to it and the control arm along with the leaf that pressure is still being apllied thusly. The only real benefit i can see from coilovers the ability to change right height without changing spring ratios. Even on a leaf setup you can get adjustable shocks so thats not somethign a coilover system will give you over a leaf setup. As well as you can raise and lower the vette on leafs but you will push its center point out of its center point. Either way coilovers are superior but i dont know if i would go so far to say you need them to win.. with the right driver and a good shock/sway bar setup you can still be victorious.
 

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Does any one else agree that the leaf spring is in the way when working on the car? I just changed the trans and engine mounts. I took me about 15 hours! It would have been a lot easier if those damn springs were not in the way.

Just my rant on leaf springs
 
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