Custom Front Suspension geometry questions - Camaro

[ericmattessich]

So a little background, I have an official build thread for the car here -> http://www.thirdgen.org/techboard/me...o-picture.html But since that's been updated I have decided to use a set of Corvette C6 Spindles, hubs and brakes to construct a tubular front sub-frame and a-arms around. I've been using solidworks for CAD (i'll try to post some screenshots tonight) and Performance Trends Suspension analyzer to check the roll centers, camber curves, etc. I think I've got it all set up where I want it but I wanted to let you guys take a look at it so if there's something that pops out as a poor design, I can refine it before I start ordering/cutting the tubing and all. I've attached some screenshots of the suspension analyzer with my dimensions inputted and the suspension analyzer file also here -> http://db.tt/JTy7sCRI. Screenshot links http://db.tt/xVe8xIIb http://db.tt/iojCzykU

Any advice you guys can give me would be great, this is my first suspension build and even though I'm designing a ton of adjustment into the system, I would love to get it pretty close in the beginning. Thanks in advance!

[Ron Sutton]

The photos are too small to read any detail.

[ericmattessich]

The photos are too small to read any detail.

please see the updated Screenshot links http://db.tt/xVe8xIIb http://db.tt/iojCzykU they should come up full size and should be very readable

[Ron Sutton]

Hi Eric,

Overall you've done a good job. I see an error and some conflicts for you to address.

You have the KPI of the spindle at 6.60° which is not correct for the C5/C6 spindle. Unfortunately, I do not know exactly what it is either, as I've been told 5 different answers from 5 different sources. If I had one in hand, I could measure it & know for sure, but I don't use that spindle. I do believe it is in the 8.7° to 9.15° range. You will want to figure this out "for sure" and recalculate your front end. That KPI angle effects your BJ locations and therefore your camber gain & roll center location ... the most important things you're working out.

A conflict I see is the roll center location and static caster. The roll center location is in the ball park for AutoX, meaning it is low statically and will go down significantly when the suspension is compressed in dive. However the caster is very low at 5° which may be "ok" for road courses with big sweeping turns, but not for AutoX or tight road courses. The factory Z06 runs 7.7° of caster and the winning Corvette racers run 9° to 10.5° in AutoX and tight Road Courses.

You didn't say your intended usage. If it is AutoX, you need to increase the static caster dramatically and leave the RC where it is. If your goal is road courses, I'd still increase the caster up around 8.0° to 8.5° ... and move the roll center up 1" to 1.5".

[ericmattessich]

Let me just start with a thanks for the input, Ron. This is pretty new to me so this is all a big help.

I'll have to check to check the kpi on the actual spindle vs what my CAD model shows, its a good possibility it's off as I got it from grabcad and only did a quick measurement check.

The eventual goal for this car is to do some road courses - NJ motorsport park, watkins glen and the very very rare AutoX. I thought the caster was a little low but I wasn't really sure what the factory vettes ran. I'll bump it up to 8.5 with a degree of adjustment available in each direction at least. Since the car will see more road courses than AutoX i'll move the roll center up a bit and see how it all looks.

[Ron Sutton]

Shoot for a RC around 1.5" in dive.

[marolf101x]

How about this for an idea?
Cut a vette in half and stick the front under the third gen:

[Ron Sutton]

Hey Britt,

Is that your project in your garage?

[marolf101x]

One of them. Supposed to be a simple, cheap daily driver.

[ericmattessich]

marolf101x I've been subscribed to to your build thread on thirdgen, love the project. It helped inspire me to go with a similar suspension setup to the C6's. Thinking back on it i almost wish i took that route but i have so many parts for the planned path i've set myself on it would have been a nightmare to sell them all off.

Ron so I did some measuring on my granite table and it turns out its 8.5 degrees KPI for the vette spindle. Thats what I get for trusting someone else's measurements. So I'm going to take some time to make a new model for myself (I'm also going to do this for the hub because I got that from the same source.) then i'll see where I'm at. I'm definitely going to work in the advice you gave me. It all sounds very consistent with the reading I've done today on the subjects.

So I have another question regarding adjustments, do you have any baselines on how much adjustment you should have on the key parameters, like balljoint location, frame pivots, steering rack location, etc. ?? I mean just by the nature of the design of rod-end a-arms there's a lot of adjustment. Do you think its necessary to have front to rear and height adjustments on the frame pivot locations?

[ericmattessich]

Oh yeah and I just wanted to point out that after I've finalized the CAD i'll upload it all to grab cad if anyones interested

[Ron Sutton]

marolf101x I've been subscribed to to your build thread on thirdgen, love the project. It helped inspire me to go with a similar suspension setup to the C6's. Thinking back on it i almost wish i took that route but i have so many parts for the planned path i've set myself on it would have been a nightmare to sell them all off.

Ron so I did some measuring on my granite table and it turns out its 8.5 degrees KPI for the vette spindle. Thats what I get for trusting someone else's measurements. So I'm going to take some time to make a new model for myself (I'm also going to do this for the hub because I got that from the same source.) then i'll see where I'm at. I'm definitely going to work in the advice you gave me. It all sounds very consistent with the reading I've done today on the subjects.

So I have another question regarding adjustments, do you have any baselines on how much adjustment you should have on the key parameters, like balljoint location, frame pivots, steering rack location, etc. ?? I mean just by the nature of the design of rod-end a-arms there's a lot of adjustment. Do you think its necessary to have front to rear and height adjustments on the frame pivot locations?

Hi Eric,

I'm not sure I can give you an unbiased opinion. As a race car designer, crew chief & tuner, I make everything adjustable in cars I'm going to run. But I tune with things the average car guy may not tune with & I'm obsessive with dialing in a set-up to the nth degree.

Only as an example: If I find 375# front springs are too soft and 400# front springs are a bit too stiff for "ideal" ... I'll either run the 375#'s with more anti-dive or run the run the 400#'s with less anti-dive. Since the degree of anti-dive also controls the degree of caster gain, I have to adjust the static caster to end up the total dynamic caster I need. plus I'll need to reset the bump steer. Most people are not going to this extreme, unless they are very, very hard core racers obsessed with winning.

Most of the manufacturers of PT front clips & suspensions don't make their stuff very adjustable for good reason. They designed it with a combination of geometry that will work good, and don't want their customers "going off the range". Changing things like UCA height at the frame (to adjust camber gain and roll center) also affects the bump steer. Designing the clip with minimal adjustment protects the user from themselves.

But you're designing yours. So I have two questions for you, that will help you decide this answer for yourself.
1. Do you plan to be a "tuner" who is changing settings to find optimum performance at track days or AutoX?
2. Are you concerned your initial geometry settings may not be optimum, and need to be adjusted?

If you answered yes to either, then you will want to build in more adjustability. If you answered no to both, then I think less adjustability is acceptable.

If you decide to make yours "very adjustable" and want guidance, just ask.

[FlyDoc]

I too have been following your thread on ThirdGen.
I had purchased Spohn k member, and A-arms when I found your thread and had wondered if I had done the wright thing going that route, sense I had all ready put a C-4Vet IRS in. I still wonder if I have done the wright thing by staying with 1982 technology for my front suspension? The A-arms that I got the lowers with the adjustable delspherical ends.
My thoughts now are, do I just go with what I got, or could I incorporate upper A-arms, and different Spindles?

Sorry if this post is choppy & rambles, but doing this while trying to get my kid with ADHD to do her home work!

[ericmattessich]

Hi Eric,

But you're designing yours. So I have two questions for you, that will help you decide this answer for yourself.
1. Do you plan to be a "tuner" who is changing settings to find optimum performance at track days or AutoX?
2. Are you concerned your initial geometry settings may not be optimum, and need to be adjusted?

If you answered yes to either, then you will want to build in more adjust ability. If you answered no to both, then I think less adjust ability is acceptable.

If you decide to make yours "very adjustable" and want guidance, just ask.

I would probably be a tuner, at least setting up a baseline for each type of track and then looking at tire heat/ wear to do a little fine tuning during the weekend. I was never really obsessive but I'm also not the "show up and drive" type. Also since this is my first time designing a suspension setup I'm not 100% confident it will be right and I really would prefer to not have to cut up and move stuff on the car once its done.

So the short of it is I could certainly use some guidance on whats important to have some adjust ability in. right now the a-arm frame pivots have adjustable rod ends, the tie rod height is adjustable and the top shock mount height is adjustable. Should I also include forward to rear and height adjustment on the a-arm frame pivots?

[ericmattessich]

I too have been following your thread on ThirdGen.
I had purchased Spohn k member, and A-arms when I found your thread and had wondered if I had done the wright thing going that route, sense I had all ready put a C-4Vet IRS in. I still wonder if I have done the wright thing by staying with 1982 technology for my front suspension? The A-arms that I got the lowers with the adjustable delspherical ends.
My thoughts now are, do I just go with what I got, or could I incorporate upper A-arms, and different Spindles?

Sorry if this post is choppy & rambles, but doing this while trying to get my kid with ADHD to do her home work!

How wide are your front tires? That's kinda why I went this route. I have a 275mm wide tire in the front and it had a terrible wear/ heat pattern. Anyway what I'm getting at is if your satisfied with the front grip and you have good wear/ heat patterns why break out the sawz-all? Just my opinion though.

[Ron Sutton]

I would probably be a tuner, at least setting up a baseline for each type of track and then looking at tire heat/ wear to do a little fine tuning during the weekend. I was never really obsessive but I'm also not the "show up and drive" type. Also since this is my first time designing a suspension setup I'm not 100% confident it will be right and I really would prefer to not have to cut up and move stuff on the car once its done.

So the short of it is I could certainly use some guidance on whats important to have some adjust ability in. right now the a-arm frame pivots have adjustable rod ends, the tie rod height is adjustable and the top shock mount height is adjustable. Should I also include forward to rear and height adjustment on the a-arm frame pivots?

Gotcha.

The key things to "tune" or dial in a track car suspension are:

• Roll center
  
• Caster
• Camber gain
• Anti-dive
• Track width (to a degree)

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Tuning with Roll Center:

Key Tip:
Static roll center at ride height is not very important. The key is the location of the roll center in "full dive" with "roll angle" accounted for. So all of my roll center numbers are based on the suspension being "in dive" to the target travel & roll angle.

Direction:
a. Raising the RC, places it closer to the CG, reducing the CG leverage, reducing roll angle … and working the front tires less.
b. Lowering the RC, places it farther from the CG, increasing the CG leverage, increasing roll angle … and working the front tires more.
c. For faster corners found at big road courses I’ve found the happy window to be 1” to 2.5” … and -0.5 to 1.0” for tight AutoX events.
d. If the RC migrates to the inside of the corner under dive … it will work the front tires more … but roll more if not controlled by the suspension.
e. If the RC migrates to the outside of the corner under dive … it will roll less work the front tires & roll less.

*KEY NOTE: For optimum cornering ability, you need to WORK the tires … and low RC’s combined with big sway bars work the tires while keeping the roll angle low. In other words, don’t use the front RC as your primary tool to control the car’s roll angle.

For the hot rod I’m designing & building for myself, I have two front RC locations. For AutoX it is 0” in dive & 1.2” in dive for road racing & high speed events. All I have to do is change the slugs in two control arms. Yes, I have big sway bars.

Just an FYI: The imaginary lines that go through the ball joints & control arm pivot points ... of the upper & lower control arms ... intersect to form a the Instant Center. This pivot point creates a "swing arm". The distance from the Instant Center to the center of the tire's contact patch is the "swing arm length."

A lot of stock production cars have the swing arms so long … there is little to no camber gain … often camber loss. Plus, in many stock production cars the A-arm angles put the roll center so low it is below ground ... and the CG is high … giving it a ton of leverage to roll the car … which is part of why many stock production cars roll so much.

Typically, when you dial in your front geometry … you’re goal is to place your RC for optimum handling for the type of driving you do (or find the best compromise) … and end up with the desired camber gain. When you are changing control arm angles for optimum roll center, you are changing the camber gain too. Use this to your advantage.

Some quick tips on camber gain:
• Anytime you’re shortening the “swing arm” … you’re increasing camber gain … regardless of how you did it.
• Anytime you’re shortening the swing arm length … & keep the IC at the same height … you’re raising the RC.
• Conversely, lengthening the swing arm length … & keeping the IC at the same height … lowers the RC.
• Anytime you’re raising the IC of the swing arms … and keeping the same swing arm length … you’re raising the RC.
• Conversely, lowering the IC of the swing arms… and keeping the same swing arm length … lowers the RC.

There are several software programs out there to calculate roll centers. I own & use several. I suggest Performance Trends to car guys & gals often because it is the easiest to use.

*KEY NOTE: When you change the swing arm IC … length or height … you are changing the bump steer … because you are changing the arc the UCA/Spindle/LCA assembly travels in. Another reason why so many people don’t like tuning on it.

For my hot rod, I have worked out the bump steer shim packets for my two RC setups … which includes a tie rod slug & shims. I simply keep a “set” for each of the 2 RC locations, making the change over quicker & easy … after the initial work is done.

Last tuning note:
Once I have tested & worked out an optimum front end set-up for a type of track … I “lock it in” and don’t change it at the track. So this is NOT something you’re constantly tuning on … just initially. At the track, the optimum front end geometry is the optimum front end geometry … so as the track changes throughout the day … we’re tuning on other stuff to keep the car “balanced”.

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I think you mentioned you're running the C6 control arms & spindle. I don't have any experience with them, but if Howe makes ball joints for them, I'd highly suggest that route. Then you can change the heights of these pivot points by changing the BJ pins.

Being able to adjust the pivot points of the control arms where they mount at the frame is key too. Slots & slugs are the tool to do this. In racing, we use twin slotted UCA mounts that weld to the top of the frame. A variety of slugs with the holes centered & offset in specific amounts, allows the UCA pivot axis to be moved up or down. The ones I use already have some anti-dive built into the slots (the front slot is 1/4" higher) ... but by using different slugs, you can increase or decrease the amount of anti-dive.




But I often run more anti-dive than that. So I may have a slug in the front slot with the hole another 1/4" to 3/8" higher than the rear hole.

Utilizing UCA's with slotted shafts, like the one below, allows for easy, high ranges of caster adjustment, without affecting camber. Shims & spacers are used inbetween the cross shaft & frame mount to adjust camber. I suggest you make sure you have the ability to shim the UCA to achieve a range of static caster from 0 to 2.0° or more.


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For my PT/Track Car, I have the LCA mounts slotted too. I can change the height of the LCA pivot 1/2" up or down (1" total). I find many guys aren't aware you can achieve the same roll center ... but with different swing arm lengths & camber gains ... by tuning on the LCA angle instead of the UCA angle. And, said another way, we can achieve the same swing arm lengths & camber gains ... but with a different roll center ... by tuning on the LCA angle instead of the UCA angle.

As mentioned above, I can change my roll center with 4 bolts & slugs. It can be achieved by changing either the UCA or LCA angles. I do mine on the LCA's, because it allows me to achieve a more optimum camber gain for each application. (AutoX & Road Course)

Lastly is small track width adjustments. I prefer to not run wheel spacers in the front if I don't have to, because they increase the scrub radius. Race series rules are usually the deciding factor. If the rules allow us to run tubular LCA's, I run rod ends and length adjusters (LH & RH threaded) that allow 1" of track adjustment on each side. So if I need to move the front track width out 1/4" on each side, I don't use a wheel spacer. I adjust the LCA's out 1/4" ... and either ... change the UCA spacer 1/4" ... or change the UCA length by 1/4" to keep the control arm angles close to what they were.

Again, this is hardcore race tuning stuff, and you may not be as obsessed with this degree of tuning as I am. But at least you know the methods available and can decide what works best for you.

Best wishes !

[FlyDoc]

I'm running 275/40-18 on the front.
I think I will start another thread, so I can get some clear answers.
I like what Ron has posted, now if I could see how it works, you now see it, feel it, taste it, & touch it I would be golden! I could read it a 100 times but tell I see it work in front of me I just can't put it all together.
I'm at the point where I'm not going to ditch what I have (the Spohn) components, but just can I add UCA's and gain adjustability.

[ericmattessich]

I'm running 275/40-18 on the front.
I think I will start another thread, so I can get some clear answers.
I like what Ron has posted, now if I could see how it works, you now see it, feel it, taste it, & touch it I would be golden! I could read it a 100 times but tell I see it work in front of me I just can't put it all together.
I'm at the point where I'm not going to ditch what I have (the Spohn) components, but just can I add UCA's and gain adjustability.

I'm guessing you have 2" wheel spacers on the front? That's what I had, wore the outside of the tire so quickly it was a waste. Hence this project.

[ericmattessich]

Thanks Ron for that great explanation! It looks like I've got some simulation and CAD work to do, I'll post up a hopefully final design soon

[Ron Sutton]

I'm running 275/40-18 on the front.
I think I will start another thread, so I can get some clear answers.
I like what Ron has posted, now if I could see how it works, you now see it, feel it, taste it, & touch it I would be golden! I could read it a 100 times but tell I see it work in front of me I just can't put it all together.
I'm at the point where I'm not going to ditch what I have (the Spohn) components, but just can I add UCA's and gain adjustability.

Hey Doc,

Start a thread and we'll discuss your project.