Jim's Giovanni

SO. The Giovanni 6 link suspension has had a number of DIY pproaches - and here is another; "JIM'S GIOVANNI"

One thing that struck me about many of the approaches - they (like the Giovanni Patent) all are securred to the differential. That has always bothered me. Typically suspension system components are part of the chassis and not the driveline.


In my approach - I chose to use the Differential carrier (crossmember) as the main chassis component - not the differential carrier itself.

I also wanted to use simple materials with an eye to making the set up easy to replicate, use standard hardware (auto/race/circletrack) and easy construction methods.
No CNC - (although I have access to one - I don't cut metal on it) and no "outsourcing."

Buy - Cut - Weld - was my mantra.

I have bugged any number of folks that have built these setups, and reverse engineed a number of approaches. This may not be ''elegant," but if it tests out as well on the road as it does in the garage (once I solve the annoying Heim Joint problem - separate link), I will be more than satisified.

So what does the Giovanni look like? Here is an image from his Patent:


Item 9 is the part fastened to the differential.

Here in Figure 3 from the patent you see the tabs for the upper control rods:



This image shows how I approached mounting to the crossmember rather than the Diff.



I built the pieces from comercially available angle ''iron." Welded 2 together ( one cut and notched as shown, and then welded to the crossmember.


Lots of weekend fiddeling with models and moving pieces around, but the results are VERY favorable (regarding Camber Change.)

For the Wheel End of business - I chose again to Buy - Cut - Weld, this time on a set of Dragvette Safety loops. They are about 100 bucks a pair and I took some time in making that decision. But the results are really good.



To modify the lower control rods (lower) I used some aluminum plate to build a set of spacers and "lowered" the stock corvette strut rod carrier with longer bolts.
]


The following graph shows the Giovanni results and mine over the same range of motion.



I have achieved less camber change over the same range of motion - for a much lower cost - and I am convinced as sturdy a setup. AND, I can drop the diff and leave much of the suspension intact!

My results are great for camber - but I need to get longer upper rods to be able to set the Toe-In where I want it.

I will be using slip joint Half Shafts from Tantons - Have them - just not installed yet. First I need to solve the slop in the Heim Joints - that is another post... (FYI http://www.vettemod.com/forum/showthread.php?t=7704 )

Çheers - Jim

Interesting write up.
I plan on doing something ever so similar myself. My biggest difference though will be that I am locating my spindles further outboard to accommodate a more late model wheel offset. Additionally, I plan to fabricate a "cradle" like most late model vehicles that will bolt in more or less factory pick-up points but contain pretty much the entire suspension/3rd member. Right now it's all conceptual, but as I get caught up on some other stuff I hope to make a little progress on the project.

clutchdust said:

Interesting write up.
I plan on doing something ever so similar myself. My biggest difference though will be that I am locating my spindles further outboard to accommodate a more late model wheel offset. Additionally, I plan to fabricate a "cradle" like most late model vehicles that will bolt in more or less factory pick-up points but contain pretty much the entire suspension/3rd member. Right now it's all conceptual, but as I get caught up on some other stuff I hope to make a little progress on the project.

Click to expand...

I too keep thinking, conceptualizing and scratching my ass, but when all said and done, I dunno WTF I"m doing, so I just read on.....

:crap::hissyfit::nuts:

I have a spare crossmember that I'm going to use with my dual mount spring. The dimensions you provided help a lot (bracket length 9 1/8") so now I can start fabbing this without removing the old stuff first

What did you modify on the Dragvette loops ?? I like the idea and will most likely copy it

Karsten - I'm so impressed with your work - and now flattered - you'd want to copy mine!

I'm learning heaps about rod ends - so save yourself some expense - unless you've got it sussed - and I'll let you know which seem best . I have the JKs on order and should be in this week.

On the Drag Vette Loops



First I ground down the stuff that would be in the way, thenI welded the tabs (well had a buddy) to the top of the Drag Vette Loops. The challenge is getting them clear of the frame bump stops. My first approach did not - and got a REDO!:


I'll measure the overhang etc and put together some pics if you'd like. And with luck I can find the part number I used for the tang - that was an "off the shelf" not fabbed.

If you fab the ones that are in the VETTEMOD (download section) - they would be ok too I'm pretty sure in this application. The main thing I was trying to get to was; "simple." Keep re-learning the KISS principle.
I haven't yet driven - still building. But, I like the results from "bench testing" and it will be a major improvement over the standard C3 rear suspension.
Cheers Jim

Thanks Jim :blush: ... although I haven't really done any true mechanical work in a while, since January I'm cutting fenders and slinging glue and mud :lol:

I already have the teflon lined rod ends, Competition Engineering, got them from Summit, C6154 (checked one of the packages), one is RH thread and one LH of course. No play whatsoever, not cheap but seems to be good quality.

Some time this winter I'll redo my entire rear suspension, got two rebuilt trailing arms with JohnnyJoints that will go in at the same time....

I noticed on Dragvette's website that two of the four rod ends are rotated 90 degrees, I prefer the way you mounted yours (all four pivoting). I also noticed they charge $120 now, do they give any discounts ?

what's a "tang" ?

Tab - Tang - Bracket -- That bent piece of metal! :clobbered:
(Tang is what I have on my mast back at the boat - and my vocabulary gets confused!)
Here is a pic that shows the "first Draft"I made. Note the part number is a close replica to the ones I used (even for the spreader bar so I bought a bunch.) Mine didn't come with the bolts or spacers. They are often used in Coil Over applications - so you can find them that way too.



Please note these were a bit of a "lesson." They worked well --BUT - would bang the chassis bump stop - so then I moved to the solution using the VetteDrag safety loops.

Karsten - you check with Vette Brakes - they might have a discount...
I too didn't like the side mounting for their solution.

Hope all that helps- WIth a bit of time I'll consolidate, pdf, and file in the downloads/tech section.

Cheers - Jim[url=http://www.vettemod.com/forum/

Is this just a quarter mile/straightline car? The lack of camber gain has me mystified.

I agree...only very slight gain from the rod length difference and as such a small difference in horizontal vector change over angle.

Very interesting. Where can I find some more info on this "Giovanni 6 link" design? I am interested in doing something new with my rear suspension, and a 6 link would be nice.

Ever since I swapped to a TKO600 from an auto this year, I am having very bad wheel hop that I would like to get rid of.

So far, it appears that the available commercial choices are either the Guldstrand unit which is very expensive, or the Dragvette unit. Pardon my ignorance on these things, but is the Dragvette unit a solid design?

One more thing to investigate is the very long swing arm.... nearly infinite!
This will cause very low roll resistance.

The Dragvette system is designed more for dragracing than for twisting, and for my opinion the connection of the upper arm to the trailing arm is too weak to be used witn a slip halfshaft.
This will force the geometry of the system in a single configuration.... the one avoiding any binding of the three arms (upper, lower and haflshaft).

Furthermore I should move the outer upper pivot lower, in order to allow more wheel travel, othervise you will be forced to a higher ride unless you will accept a short compression stroke.

....my 2 cents....

Thanks all -
Much goodness in the observtions and comments I'm sure.

For more info on the Giovanni Rear Ssupension here is a link to the patent itself:
http://www.docstoc.com/docs/4133929...-Wheels-Camber-Angle-Setting---Patent-5046753

You can sign up and download it for free.

I'm on travel this week and don't have access to some of the other notes I've collected on it and similar approaches. But, the source will be a good place to start. Corvette Fever did a 5 page article on it in the early 80s. I have it but it is at home plate. It was a tremendous improvement in the C3 handling. By adjusting the upper and lower struts you can effectively zero the toe so both rear wheels are parallel under cornering load - so they say in thir observations.
For now, its where it is on my vette. Up on horses waiting for me to return and do some more work. Hope to get it on the road - sometime and give it a "spin."
From best to worst - it will be somewhere in the middle - BUT, not a huge investment. So far some welding time, angle iron, and about 150-200 bucks in rod ends. The Safety loops I was goint to get anyway - but thats another 100-ish. The Stoker427 - elegant six link setup is a fabrication effort that would be on the order of the C5 Mod ans I looked at the challenge there. Not panning it - just saying, costs add up.

So for CAMBER and TOE control from a cost perspective I offer;

1. The best maybe a C5 modified double wishbone set up - used bits for about 1500 complete with tranny.
2. Stroker427 6 Link
2a.
3. Real Giovanni
3a. Other Giovanni approaches FLEXUS, METALKID, Norvall Willhelm, etc
3b. My Giovanni (Only testing will tell if it even belongs on this list!)
4. DragVette (I don''t like their approach to mounting the upper outboard rodend.) Even though it costs more that the above 3a, 3b, it rates lower in choice.
5-6-etc somewhere in the mix ought to be the SharkBite Kit too.
DEAD LAST:
Stock C3 Rear Suspension
+++++++++++++++++++++++++++++++++++++++++++
Rear Suspension Mods that offer little/no CAMBER/TOE CONTROL But improvements:
1. Coil Overs
2. Fiberglass Spring
3. Johnny Joints on TAs
4. Aluminum mounts on Diff, Diff Carrier
5. Poly bushings on Sway bar
6. Smart Struts - NOTE: Herb Admans first recommended dropping the lower mount 1/2 inch in early 1980s!
etc, etc.



AGAIN DEAD LAST:
Stock C3.



Hey - Its gonna work out - I'm sure. (No fool - like a confident fool?)
And - yes Straight Line, autocross, and sometime daily show skitzo car. Life is full of compromises. And this approach shows just how I made some. More to follow once I have a bit of time to collect the pages, pics etc.

Cheers - Jim

My take on it...

A 6 link is a load of hogwash if you have a dif w/ o splay on the stub axles. Sure it's nitce to unload the halfshaft but then use it to your advantage. use a telescopic halfshaft and move the uypper rod to get a proper instantaneous center location, respectful roll center height and camber gain profile. The biggest problem is the crappy toe control, none of these tackle that issue.

In your list you forgot 84rzv500r, he took the proper approach to camber gain and eliminating the halfshafts from the equation.

Everyone that uses a stock halfshaft is restricted to the geometry set by it and the loer arm. Get it wrong and stuff will start to bind badly.

Sure it looks cool but why not make it so it's actually imrpoving the rear suspension? Taking camber out is a bad idea. Like stroker says, because of the parrallel rods there is no IC (it's @ infinite) and this means that the roll center height is very low, @ ground level. Now, roll center offers roll resistance but it also gives a jacking effect if it's too hgh. This is the trade off here, the lateral tire force created a moment arm over IC to tire contact point This will give a jacking force if the RC is aove the ground, more if it's higehr and anti jacking if it's low below the ground. This means the unsprung mass will have a vertical delection due to the lateral load and the direction of this deflection is related to the RC height. Being a road car the RC is centered, so let's not discuss offset suspension with offset RCs to aid in jacing (roundy round cars)

Think of a pole vaulter, the RC height is where he sticks his pole in the ground...so he comes running up to the bar and then sticks it @ ground level. Sure, he comes up. Now he does it again but the pocket for his pole it @ 20" off the ground, sure makes it harder to make the fosbury flop

As for centering the rods to set toe to 0, when your wheels moves up and down the halfshaft changes angle, this reduces the effective horizontal length. The same for your rods. They are horizontally at their longest when they are horizontal. Any deviation from that efectively shortens them in the horizontal vector and this pulls the hub invoatd. this means the toe moves to TOE OUT!!!! The only way to remedy this is by removing the toe control from the trailing arm and have a geometrically proeprly located to control rod like C4 (but can be done better w/ 2 rods like the greenwood C3 IRS, the C4 stuff is a cheaper version by meddling beancounters). If you want to retain the stock trailing arm, the only way to "patch" the problem is to stiffen up the suspension so that the vertical stroke is limited and setting the halfshafts to around horizontal @ loaded ride height so the stuff oscillates around that orientation. This because the greater the angle the larger the vector efect on the horiz. component.

Coil overs do nothing but add adjsutability. A lea spring can do just the same, especially a dual moutn spring with wide apart mounts. Because of the way the spring reacts to loads on either side it offers both spring and roll resistance. I posted a snippet of that some time ago, it was from a book about the C dual mount rear spring. An eye opener for sure.

Smart struts ar junk, they too reduce the camber curve. these are sports cars, supposed to go around corners.

You might want to take a look at what happens to your geometry with body roll. With no camber gain, 2 degrees of body roll wil produce about 2 degrees of toe out on the outside (loaded) tire.

What size are those allen screws holding the bracket onto the trailing arm?

I agree totally with Marck !

Unless you will remove the trailing arm..... no way to reduce roll (bump) steer.
Only solution with the original TA is nearly rock solid springs!!!!

Stroker-427 said:

I agree totally with Marck !

Unless you will remove the trailing arm..... no way to reduce roll (bump) steer.

Click to expand...

Roger that - Number 1 on the list -- Dual wishbones...

It is what it is...just sharing an approach... later I'll share any lessons learned - not just theory(and please don't anyone take that as an affront! It is what I do... Design and test. Refine & revise. If it works - I keep it - if not --toss it and move on.)

Theory is fine, but it is in the application and modification that it becomes real. This is still a C3, just making improvements in as cost effective manner as possible.

Hope I haven't hit a nerve - that is/was not intended - but please with your experience, and theory-- share some specifics. I found very little direct application to the C3 - and I spent a lot of time looking at forums dating back to 03. Nothing codified or clear - and few that didn't mount directly to the Diff (pumpkin) - which seems like a waste of effort, which is why I went to the carrier.

1. But to continue, the SharkBite is "poohpoohed" because the angles are "wrong" for the coil mounts - yet it reduces unsprung weight. So -- What is the correct angle for a C3? Nothing heard?

2. The DragVette is suposed to be a low end cost version of the Giovanni - it seems to be -- but reviled as - "FOR SAFETY only!"

3. Seems like Corvette Fever tests were all off base - but that was in the 80s - and the C3 is at BEST late 60s tech - so any improvement is good.

4. Flexus did a bit of designing then abruptly lleft the scene.

5. METALKID has been "messing about too. Any "Expert advice offered?" I've seen none.

This seems to be an excellent opportunity for anyone else to offer their Rank Order Listing of improvements (citations much welcome, design and engineering specifics most welcome.)


But more specifically, focused on the Rear Suspension, If you have some specific design (dimensions, etc) for consideration - I'm sure many would appreciate those -- I know I would.

Is that a GAUNTLET you heard dropped? hmmmm. maybe...

Cheers - Jim

[Special Note: If my RANT offends - I appologize it is not meant to.
Many C3 owners would like to find a reasonable (read affordable) set of improvements to the rear suspension - and I am one. I have only offered my approach for consideration - and I HONESTLY - and I mean that - honestly, thank you for your review and critique. But others might need more. Stroker-427s is an example - Much detail in terms of the build, and I have not sourced a clear discussion of the design - the why and what of thelayout. And, there is no cost to benefit trade off , gains in control per $ invested. Yet to be made -- any engineering comparison modified to stock. If I have missed these in my research - again, I apologize. If somewhere - please cite for my study.]

BBShark - You'll have to wait until I can get back to home plate to verify - 1/4 - 3/8 I'll have to check. end - and do I sense your concern - shear?

The dragvette system is a safety device, not controlling.

The prob w the sharkbite is the cam ratio.

Ideal shock / spring rate is as close to wheel rate as possible.

Sent from my GT-I9000 using Tapatalk

You don't have any reason to apologize! :thumbs:

Sorry if I'm not so clear in my writing..... you can imagine that isn't so straightforward for me.

Anyway before to cut any piece of steel I did lots of drawings, readings and thinking.
Basically I was looking for a system able to better control the wheel stroke, able to generate the correct roll steer (for my opinion you will need some toe-in during bump) and able to generate the correct camber gain for the tiresI have in my car (really this thing is strictly related to the kind of tires used).

Furthermore in my design there is the possibility to adjust bump steer (in both ways) and camber gain and swing arm (basically moving up and down the inner lower pivot point) ena per consequence the roll center.

Of course I didn't pay any attention to the cost/benefit ratio....... I was only looking for the best solution I was able to design and to realise.

For example right now I'm trying to design new fabricated front hubs and spindles in order to reduce the scrub radius and to have a better king-pin angle.

My car is a continuous work in progress project..... I really like the thing..... and I really like to test drive the result of my efforts in race tracks (next time will be december 4th in Franciacorta racetrack).

Right now I have no problems in being faster than C5 and C6 and Vipers..... the Z06 is a stronger rival..... but I will do my best (at the track and in the garage).

My knowledge in suspensions is coming from many books and from my experience during the days of racing in the Italian GT Championship in 1999 and 2000...... when nobody was racing seriousely with these cars.

Sorry if I'm not so clear...... I'm doing my best!

Like Stroker 427, my car is a continuous work in progress. I am now far enough along with my most recent body/aero mods that I will now be able re-engage the rear suspension issues. I have given up on trying to modify a C-4 rear upright to add an upper link, so I am building an upright that will have the forward, lower, and toe link geometry of the C-4 piece, but will have an upper link mount and will accomodate a C6 ZR1 bearing/hub. I will use C6-style axles with CV joints (heavy duty, custom length). Right now I have Tom's stub axles in a C-3 differential which I can modify to accept the inner CV joint, but I'm working on a grander plan. The Driveshaft Shop recently released a Ford 9 inch-based IRS center section for late model Camaros. It is very strong, and, with a little modification, I think I can make it fit my car. I am choosing CV jointed axles in lieu of sliding splines to eliminate any potential of binding of the splines under load that could cause an unexpected change in handling. I'll post as I progress.

Really enjoyed this thread. If you (I) were too build a double wishbone setup what sort of geometry would we look for. LOL! From all the reading I have done I'm in the neutral design camp as of now. No special effects, looking at an F1 design, I see a really straight forward design that costs a fortune. No anti-squat, special toe control, etc... No I don't think I'm a F1 kinda builder. But if you also look at any front suspension, you never see fore and aft links, 6 link etc.. Tried and true it seems, double wishbone.

My two cents on the dragvette design. I can't imagine ever trying to street a car with this setup. Cornering would be nil. Body roll trying to drive the outer edge of your tire into the pavement. Total bind, the ass end would ride like a go-cart.

http://roadstershop.com/blog/2011/roadster-shop-fast-track-irs-overview/