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5-Link Design Consideration

 
Old 03-13-2019, 12:48 AM
  #21  
gkull
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Originally Posted by 69427 View Post
Doesn't matter if you agree or not. It's simple suspension geometry. If the car leans in a corner, and you have zero camber gain, your outside wheel/tire (the one doing the majority of the work back there!) goes into positive camber relative to the road surface. Positive camber is not the hot setup for cornering traction (your tire contact would just be the outside portion of the tread, not the whole tread).

Camber gain is the whole reason for the SLA suspensions in most vehicles. (IIRC, old Volkswagens had zero camber gain setups in the front ends.)

You can add static negative camber back there, but you're just bandaiding a geometry shortfall.
Camber gain is a good thing if the amount is consistent with all your other components. I was trying to say that you can't use the built in 1970s and 60 series tires large gains with modern 30 series tires with minimal body roll. I should have said next to no camber gain instead of no camber gain.

So a static negative camber will make the tire correct when the terrific bending forces are trying to make the wheel go to positive camber

Last edited by gkull; 03-13-2019 at 12:56 AM.
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Old 03-13-2019, 01:19 AM
  #22  
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Front to rear camber gain is a very technical conversation!

To simplify it to the most extreme, I shoot for keeping my drive wheels as square to the ground as possible! Whether that is in a turn or going straight! One reason why I like all of those heims and spherical in the back, as they will attempt to self tune all of the different components, being that the tire is trying to stay flat, and likes flat the most! In my case, the more heims and spherical the better! The collective rotation customizes itself, as there is input from traction, road irregularities, suspension travel, etc etc etc. I kind of wish the human body had spherical and heims, as your knees, elbows, ankles, your spine are restricted way more límitedly in movement that something that will self swivel or rotate based on demand, feedback like a spherical or heim.

As I have said in threads in the past, operating on heims and sphericals can be hazardous on the street! I think there are only two cars brands that use them in production- some Porsches and some Ferrari’s! They can cause your tires to be grabbing every road irregularity that exists! The car can wander, track dangerously, etc. If you operate these on the street, then you better stay on top of your driving! These fancy vintage rear suspensions I have are full of heims and sphericals! So why I bring this up!

The front!!!! Camber gain is complicated and actually limited by Steering, potential bump, Ackerman, etc! A lot going on up there! You can bump tune, for your sweat spot! Yet again, I look for having the front suspension self tune! But you have ball joints and tie rods, you can have spherical in your shocks, the arms are an equation where you want steady and sure, and free movement! Why rigid solid bushings were good on our cars!

I personally think the front is what you have to work with in dialing in the balance and front to rear characteristics, but after the setup up of the back, which can net the most competition advantage, if you can get that working great, then I balance out the front afterwards with things like tire pressures, camber, caster, toe, bump, shock settings, tire size stagger or four corner square, cross weighting, spring rates, sway bar size to dial it as best as possible to compliment your rear suspension set up! If you can’t get an advantage! Then just tune and align the front to not cause you to lose.

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Old 03-13-2019, 09:39 AM
  #23  
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Originally Posted by ignatz View Post
Once camber is set to the tire's maximum grip the optimum cornering is to have the camber gain match the body roll angle. VB&P's "smart struts" always seemed to be a misleading marketing gimmick. It improves longitudinal grip for drag racing but reduces cornering performance. I tried in vain to find actual data on (say) coefficient of friction vs camber angle for a modern autocross tire to get an idea how much this matters. I know I've seen it published in some older handling books.

But, changing the discussion parameters a little, since it is not so easy to change the camber gain in the front, how can the mismatch of reducing the rear camber gain vs. the front not make the car a bit tail happy in corners? i.e. "for those who like to oversteer".
I think the Smart Struts work as intended. They allow a lower roll center and ability to adjust camber gain on jounce. VB&P instructions state:



Evidently they are thinking you use the lower setting on the street and the upper setting for racing.

Interesting to note that the '63 through '67 Vettes were set up with a higher roll center and more camber gain. Then in '68 they lowered the inner pivot of the strut rods which lowered the roll center and reduced camber gain.The Smart Struts lower the pivot point even more. I plotted out camber gain a while back at the various settings.


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Old 03-13-2019, 10:15 AM
  #24  
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Good explanation of how the lower inner strut connection limits camber gain. They also get into static neg camber

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Old 03-13-2019, 10:50 AM
  #25  
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Thanks TCracingCA

I used Greenwood lower Arm arrangement as a reference in my 80. I use a heim joints and run a rod from the front of the rear spindle to a point on the frame close to the front diff mount. Distance from car center for my front mount is the same as the rear link on the diff. This creates the triangle.

My biggest question is what I should do with the pick up points to optimize roll center. Make the lower link parallel then adjust the top a arm inner point down to set camber gain?

Camber gain is 1.5 on car now
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Old 03-13-2019, 11:13 AM
  #26  
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Sorry to hijack, but why is there not a direct fit coil over setup that goes where the rear shocks are mounted?

-Stroke
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Old 03-13-2019, 11:21 AM
  #27  
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Originally Posted by Kid Vette View Post
I think the Smart Struts work as intended. They allow a lower roll center and ability to adjust camber gain on jounce. VB&P instructions state:



Evidently they are thinking you use the lower setting on the street and the upper setting for racing.

Interesting to note that the '63 through '67 Vettes were set up with a higher roll center and more camber gain. Then in '68 they lowered the inner pivot of the strut rods which lowered the roll center and reduced camber gain.The Smart Struts lower the pivot point even more. I plotted out camber gain a while back at the various settings.


One instant mod for a better C2 rear suspension set up, is change to a latter 68 and up camber bracket! As the reduced roll center is a good thing!

I actually should not knock this particular product, as I actually have never bought this setup, used it, worked with it, or even really studied it!

There have been different brackets, with a change of geometry and even what they call a camber plate or block to drop the bracket location! And then I run good old fashion heim end rods! I guess I am in the school to pursue a suspension geometry that is set up right, and this product gives one depending on what you have, a way to dial that in for a wide range from stock components heading toward race! Locking these in would be my concern! In my suspension, I have cotter pinned things, safety wired things, etc to not ever loosen or move!

I am not a fan of stock components under the car, but for the majority that have stock component based suspensions, it fills a niche! Seems like a product that heads a Corvette suspension into the right direction!

Most of of these components should be scaled much like the Guldstrand catalog components were! 1 being pure street, 5 being performance, and a 10 being full race! Such would help an individual marry the components together to a certain planned level of performance! So where do we score the smart links, maybe for usage from a scale from 1-6, or 1-7?

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Old 03-13-2019, 11:42 AM
  #28  
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Originally Posted by Strokemyaxe View Post
Sorry to hijack, but why is there not a direct fit coil over setup that goes where the rear shocks are mounted?

-Stroke
finally an easy question! Strength of the shock mounting points. they were never designed to hold the weight of the car. only compression and rebound TQ.
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Old 03-13-2019, 11:47 AM
  #29  
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Something many don’t know, is that Guldstrand in the early days during the 1970s was a Vette Brake product distributor! He actually pirated away from of their designs like the bump steer blocks, the longer spring bolts, and a few other pieces! He was really good at spotting something like the Riley multi-link suspensión of about 1977/78 (have to go look at those first advertising offerings again), and he offered others on outlet and advertising to sell products, incorporating them into his product line! Many of the parts development and the preferred trick piece taken from everyone racing! Companies like Moog came out with HD components! The Chevrolet parts outlet sold stronger upgrade things!

The Pacific Coast Championship Race and the Guldstrand car he raced was very old school with like truck springs cut, and beefier shocks! The Penske 1966 was actually pretty stock! The real Corvette handling improvements really started hitting their stride with Delorenzo and the Owning Corning Team (there is a small almost pocket sized book that details there mods) and Greenwood (if you can find a Briggs Chevrolet catalog, you will see the HD parts, as that was the earliest catalog where I have seen the stuff- and pre-Guldstrand catalog), Greenwood who started out more of a truck spring, beefier shock guy himself too, but evolved! Guldstrand basically did assemble the truly first performance and race Corvette suspension catalog! I have most of them! In an article in 1971, he authored the suspension mods to race a Corvette! Even though many around the Country were doing these mods, he I think was the first to share what everyone was doing with an article! I can go get that mag and month year, article! I have the actual article too, but would have to find it!

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Old 03-13-2019, 11:49 AM
  #30  
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Originally Posted by TCracingCA View Post
Most of of these components should be scaled much like the Guldstrand catalog components were! 1 being pure street, 5 being performance, and a 10 being full race! Such would help an individual marry the components together to a certain planned level of performance! So where do we score the smart links, maybe for usage from a scale from 1-6, or 1-7?
It's sad the VB&P are gone. I bought the Smart Struts from them back in the 80's and I still have them on today.
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Old 03-13-2019, 11:53 AM
  #31  
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Originally Posted by gkull View Post
finally an easy question! Strength of the shock mounting points. they were never designed to hold the weight of the car. only compression and rebound TQ.
Also the location is pretty restrictively tight and even tighter as you lower the car for performance! The lower support shock mounting is pretty crowded too, and those springs add diameter to what area was just designed for a shock fitted. Plus that shock pin (single sheer), etc Maybe not good to run race rate springs on! I would suggest cutting some out of billet.

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Old 03-13-2019, 12:22 PM
  #32  
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Originally Posted by DaveL82 View Post
Thanks TCracingCA

I used Greenwood lower Arm arrangement as a reference in my 80. I use a heim joints and run a rod from the front of the rear spindle to a point on the frame close to the front diff mount. Distance from car center for my front mount is the same as the rear link on the diff. This creates the triangle.

My biggest question is what I should do with the pick up points to optimize roll center. Make the lower link parallel then adjust the top a arm inner point down to set camber gain?

Camber gain is 1.5 on car now
The inner camber rod pickup point, whether that be latter bracket, blocked bracket, smart struts, or other, we would need to know where that is! I see some great engineers on these forum threads plotting out suspension geometry! I was using a computer program there for awhile to do a virtual model! You have to pick you upper rod connecting locations! Whether that be a custom fanned bracket off of the rear diff, or a bracket welded to the rear crossmember and then I have seen different ideas on connecting to the support and trailing arms!
The best I have seen was the guy who was working up a Stainless boxed upright in the Greenwood style in a thread awhile ago! He seemed to have designed in the most advantageous geometry that would fit under our cars! If I get into work, I can load a picture of that beautiful piece!

Uestions to you, would be how much suspension travel are you looking to have? How much body roll do you think is permissible? With fitted larger back spaced clearances tires, some using larger than stock Diameter rims, etc many more variables!

My use of a program was more trying to design something to fit rear coil overs! My Guldstrand aluminum uprights have a lower and some clearance, but I think that wasn’t by design, but by accident! A good accident!

The things that gets me, is independent individual side camber gain. I just think body roll kills the best attempts at engineering a reasonable and needed camber progression! Yes street cars need more, to deal with real World wide ranging suspension challenges, but to put it simply—- I just like the car to handle flat, and mainly from four corner springs, not sway bars, and then keeping those tires square, with tracking tire footprint swivel!
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Old 03-13-2019, 12:46 PM
  #33  
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Ps I am probably not the guy to talk street engineered multi-link suspensions with! What!!!!! I probably get about two inches of spring compression and an inch of extension max, because of my liking heavy rate springs. Therefore the camber gain I worry about is probably in the 1.5 inch range max! As I run heims and sphericals, I don’t want to sheer those or end up in bind or riding on the suspension travel stops (but mine are chopped to just about a 1/4 of height!

My biggest enemy is bad potholed, or dips and holes! Basically have to slow way down, if even a simple short stretch is all tore up. If I hit this stuff at speed, the cars just kind of violently hits and skips over, maybe the tire doesn’t even drop into a hole, but whacks it! Overall if driving on the street, I am just doing my damnest to just get it there! Or where I go play, the roads are better maintained!

When I have found myself driving the cars on the street, I have changed the springs and shocks, and might even throw on some thicker sway bars to compensate, just in case I what to race a Lamborghini still!

But if I am going anywhere at all, where I will be out playing with lethal handling cars, or have a chance encounter, I will leave the Corvettes in full lethal mode and just bare and grind my teeth in the street commute, to get someplace! The last thing I want, is to be embarrassed by like a Nissan GTR or similar!

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Old 03-13-2019, 02:58 PM
  #34  
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Originally Posted by TCracingCA View Post
Something many don’t know, is that Guldstrand in the early days during the 1970s was a Vette Brake product distributor! He actually pirated away from of their designs like the bump steer blocks, the longer spring bolts, and a few other pieces! He was really good at spotting something like the Riley multi-link suspensión of about 1977/78 (have to go look at those first advertising offerings again), and he offered others on outlet and advertising to sell products, incorporating them into his product line! Many of the parts development and the preferred trick piece taken from everyone racing! Companies like Moog came out with HD components! The Chevrolet parts outlet sold stronger upgrade things!

The Pacific Coast Championship Race and the Guldstrand car he raced was very old school with like truck springs cut, and beefier shocks! The Penske 1966 was actually pretty stock! The real Corvette handling improvements really started hitting their stride with Delorenzo and the Owning Corning Team (there is a small almost pocket sized book that details there mods) and Greenwood (if you can find a Briggs Chevrolet catalog, you will see the HD parts, as that was the earliest catalog where I have seen the stuff- and pre-Guldstrand catalog), Greenwood who started out more of a truck spring, beefier shock guy himself too, but evolved! Guldstrand basically did assemble the truly first performance and race Corvette suspension catalog! I have most of them! In an article in 1971, he authored the suspension mods to race a Corvette! Even though many around the Country were doing these mods, he I think was the first to share what everyone was doing with an article! I can go get that mag and month year, article! I have the actual article too, but would have to find it!
I worked on historic road racing cars. I'm surprised that Americans were so stupid and didn't back engineer things like the bullet proof jaguar 6 link IRS setups with inboard disk brakes from the late 50's and early 60's. Even things as simple as Panhard rods and 4 link setups in solid axle cars from the same era in Europe. Only because Guldstrand and others racing in Europe and the teams coming to the US did he figure out his own 6 link 8 - 10 years later.
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Old 03-13-2019, 06:05 PM
  #35  
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Originally Posted by gkull View Post
I worked on historic road racing cars. I'm surprised that Americans were so stupid and didn't back engineer things like the bullet proof jaguar 6 link IRS setups with inboard disk brakes from the late 50's and early 60's. Even things as simple as Panhard rods and 4 link setups in solid axle cars from the same era in Europe. Only because Guldstrand and others racing in Europe and the teams coming to the US did he figure out his own 6 link 8 - 10 years later.
The Corvette was just brute power, and has always had a bad wrap in Europe! Even when the big bad ZL-1 monster motors were taken over there, the Porsche RSR and Turbos, BMW CSLs and 320 race cars, etc would dust them off!

Naturally Chevrolet wasn’t putting forth factory efforts, as the parts support network, as geared more for amateur Racing!

I like the vintage racing, because sometimes you have such a variety of different class cars, it is educational! I was watching the Tommy Bahamas yellow Trans Am Corvette going against some dated NASCAR racers and dusting them off! But then they had an IMSA GTO Nissan just blow off that Corvette, as they were leaving peak day Can Am cars behind!
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Old 03-13-2019, 09:02 PM
  #36  
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Originally Posted by Kid Vette View Post
Interesting to note that the '63 through '67 Vettes were set up with a higher roll center and more camber gain. Then in '68 they lowered the inner pivot of the strut rods which lowered the roll center and reduced camber gain.The Smart Struts lower the pivot point even more. I plotted out camber gain a while back at the various settings.

Interesting that you did this. Was this done analytically or on an actual car? I am wondering how to convert this into an actual dimensionless gain? I think it is just the axle position divided by the half shaft length that determines the triangle and accompanying included angle.

Last edited by ignatz; 03-13-2019 at 09:04 PM.
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Old 03-14-2019, 07:54 AM
  #37  
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I plotted it out in CAD.



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