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Discussion Starter · #1 ·
Howdy ya'll,

So I've upgraded the rear spring to the VB&P Dual mount, put 550 lb coils up front, and have Bilstein heavy duty shocks all around. I run lower profile tires (255/50x17) and have updated the bushings front and rear with Poly. I have the stock sway bars.

For street and even some spirited driving it's great; stable but not too harsh. However, I still feel more twisting and body roll than I'd like when getting particularly agressive with the go-pedal on a curve .

The following are the things I have in mind to improve the situation, but wonder from those of you who have experience, what the priority should be:

- Shock tower brace (VB&P make one as well as Gulstrand)
- Bigger sway bar(s)
- Some kind of hardening foam (don't know much about it, but apparently there is a foam that hardens and can be injected into the frame rails that substantially increases torsional rigidity)
- Shark bar? I know it's for seat belt harnesses, but considering its construction, I wonder if it has much of an impact on reducing twist.
- Body mounts (I still have the stock body mounts, so some sensation of weight shifting may be coming from deflection of the body mounts.)

Thanks guys.
 

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Do you think you are currently balanced...with oversteer vs. understeer? That will help identify which area to focus on first. I have almost got the exact same setup (front mono spring on 3rd stiffest, rear daul mount on 3rd stiffest, BB front sway bar, blistiens, 18" wheels) and my car does not lean at all. In fact once i get it back on the road will be adjusting the settings to 1 more softer front and back to get a little more feel of body roll. She sticks like glue though now going around a corner with the 18" wheels. Before with the 15" wheels she would just start sliding sideways with no warning....again no leaning and the 15" tires were not up to gripping like the 18" are..

btw...the Shark Bar will do nothing for stiffness. I have one and it is a bolt in type of application. You need to extend the mounting points through the floor board to the frame....then it will help stiffen things up.
 

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Howdy ya'll,

So I've upgraded the rear spring to the VB&P Dual mount, put 550 lb coils up front, and have Bilstein heavy duty shocks all around. I run lower profile tires (255/50x17) and have updated the bushings front and rear with Poly. I have the stock sway bars.

For street and even some spirited driving it's great; stable but not too harsh. However, I still feel more twisting and body roll than I'd like when getting particularly agressive with the go-pedal on a curve .

The following are the things I have in mind to improve the situation, but wonder from those of you who have experience, what the priority should be:

- Shock tower brace (VB&P make one as well as Gulstrand)
- Bigger sway bar(s)
- Some kind of hardening foam (don't know much about it, but apparently there is a foam that hardens and can be injected into the frame rails that substantially increases torsional rigidity)
- Shark bar? I know it's for seat belt harnesses, but considering its construction, I wonder if it has much of an impact on reducing twist.
- Body mounts (I still have the stock body mounts, so some sensation of weight shifting may be coming from deflection of the body mounts.)

Thanks guys.
I think your on the right track with your list. However, I can't see how any would make a noticeable improvement in torsional rigidity. In the thread referenced above, Turbo84 has observed the perimeter frame rails "bowing". In addition a C3 is pretty flimsy in the rear kickups.

I don't know if this could be done but, the X brace that was added to C4's when they introduced the convertible (1989?) was said to be a major improvement is chassis rigidity. I realize a C4 does not have a conventional chassis but it seems a similar component could be made for a C3.

Let us know what you come up with. Certainly a lot of people interested in this.
 

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Excessive body roll is a fact in our cars that comes with the design. Bigger bars and heavy spring reduce it, but also make the ride harsh and make the tires follow the surface less correct.

If you really want to do something to your suspension and as far as my .02$ go you need a guldstrand 5-link or equivalent (or even better a 5-link with an extra upper arm) to prevent rear toe-in change. You also should consider changing roll center height (don't know anymore if it need to go up or down..) and you would have to redesign the steering arm pivot points in order to get it more in line the the lower control arm and prevent bump steer.

Some of the modifications are quite extensive and expensive..., but it definatly would make your car handle better.

And then, you still will suffer from insufficient frame stiffness.

Some people will say some things are better left alone...
 

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Roll Cage Roll Cage Roll Cage


:laughing: :rolling: :partyon:
 

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Excessive body roll is a fact in our cars that comes with the design. Bigger bars and heavy spring reduce it, but also make the ride harsh and make the tires follow the surface less correct.

If you really want to do something to your suspension and as far as my .02$ go you need a guldstrand 5-link or equivalent (or even better a 5-link with an extra upper arm) to prevent rear toe-in change. You also should consider changing roll center height (don't know anymore if it need to go up or down..) and you would have to redesign the steering arm pivot points in order to get it more in line the the lower control arm and prevent bump steer.

Some of the modifications are quite extensive and expensive..., but it definatly would make your car handle better.

And then, you still will suffer from insufficient frame stiffness.

Some people will say some things are better left alone...
Me thinks you have no clue what you're talking about. It has nothing to do with being designed in, the CG and roll centers are hard to change (roll centers easier than CG obviously but moving stuff around will quickly do some good and some things are easily changed or reduced in weight) but the rest is easily changed (shocks, springs, sways) and they give you a lot of room to work with. A 5 bar will not change the roll characterstics of the car one bit, that's a factor of the springs, shocks, sway bars, Cg and roll center height (axis) A higher roll center will reduce roll, same for a lower CG. Roll is caused by lateral weight shift, not vice versa. This means that if you use any kind of solution to reduce body roll you will put that energy (force) that does not go into the suspension by rolling (springs and shocks) into the tires, reducing the slip angle.

A car that has little body roll, a smooth ride, plenty of suspension travel for rough streets and doesn't use thick sway bars......, if you can figure that one out you can make a shitload of money, all the race teams will be waiting on your input.

The 5 bar does nothing for roll, it corrects the toe control problem and is effective at that. It also offers a better adjustability and the ability to run a long virtual forward swing arm whilst still using short locating links. A 6 link/5 bar combo has no benefits. The additional upper rods of the 6 link only relief the halfshafts of their geometry functionality, however it does not per say improve the function. The halfshafts do the job just fine if your stub axles have little to no play. Something easily set up if you know how to work on your posi.

The tie rods should not run low an parallel to the lower control arm, they should run in compliance with the front arm geometry, this means w/ the pivot points and the instantaneous center created by these arms. It's not only the height, it's a vector issue, length, angle or in vertor terms cartesian vector coordinates.

So, to summarize, if you stick with the stock soft shocks, the soft springs and add a 5 bar and a 6 link, it won't help a damned thing. Bump steer improvements will always do good. Reducing the roll is not all you're after, if you reduce roll you need to create more grip and this is not only done by improving the tires but also by altering the camber curve to suit your roll characteristics.

Some people will say some things are better left alone...
Some people will say some things are better left alone...for a reason!

Then again, a 5 bar does look impressive on a show & shine car ;) :D
 

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Discussion Starter · #12 ·
. . .
Some people will say some things are better left alone...
I may be getting close. I opted for the Dual Mount Mono spring and heim-jointed camber rods for the rear. I was originally planning to go for the Guldstrand 5-link with his coil over setup. Awesome I'm sure, but you couldn't buy a cup of coffee with the change from $4,500 after installation. At that point, may as well seriously consider one of those frames that accept a C3 body and C5 driveline (I run an LSx).
 

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Discussion Starter · #13 ·
Do you think you are currently balanced...with oversteer vs. understeer? . . .
Seems to depend on speed. Especially when entering a sweeping curve at speed it starts off with a hint of understeer, then rather quickly can shift to oversteer. It's not chaotic, but you do have to be paying attention.
 
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