'71 Camaro Control Arm Redesign

[searly71]

Hello all. I'm a new member here...I'm from Mesa, AZ (near Phx) and I've got a '71 Camaro SS that's an 'all original' (for now) daily driver.

I'm a mechanical engineering student at AZ St Univ and I'm designing upper and lower control arms for my '71 as my senior design project (I'll be graduating in May!). I'm getting started in studying chassis design and choosing the angles and lengths. Once I know the geometry I want, I'll create a CAD model and do a stress analysis, then fabricate the uppers and install them. I'm looking for advice/comments anyone has on any of these things:

*perceived OE alignment angle shortcomings (like very little caster)
*experiences with tubular arms (from global west or heidt's or wherever) and their alignment angle changes
*chassis software recommendations (right now I'm using Perf. Trend's Susp. Analyzer demo)
*x,y,z coordinates of pivot points (ball joints, etc) for inputing into chassis software...I'm going to try and measure these today
*anything else that might help

Also, does anyone know what years the control arms on a '71 are interchangeable with? I think the uppers are the same from '70-'77, but not sure.

I'll be glad to share everything I learn from this...THANKS...

[yody]

I believe late model impala SS's use the same contorl arms. Also speedtech makes second gen arms. I believe on these cars, the only thingi really beneficial to change is the caster gain.

[dennis68]

Caster does not "gain" throughout travel. It is a static measurement and remains consistent through bump/roll.

Camber gain is not typically a factor controlled by control arm design, minimal gains can be acheived but you are better to design arms that help the package (including redesigned spindles). Some longer arms would be beneficial as then you could suck the wheel in more and reduce scrub radius. Good luck.

[yody]

thats what i meant, that you can gain a few degrees of caster swtiching from stock arms to aftermarket. Sorry i am not a genious and didn't use the word in your correct way.

[David Pozzi]

I think the upper control arm bushings from 74 up are larger OD but otherwise they are the same.

Camber gain is not very high but better than a first gen Camaro.
Bump travel is limitted especially if you lower the car.

[searly71]

Thanks for the replies guys...I'll check out those speedtech arms Yody.

Technically, the caster can change...it is just usually very small. If the upper control arm mounting points are angled upwards (for anti-dive), then the caster will change during compression & rebound.

Ideally, I would design an entire subframe, but I don't really have the time/money/expertise to do that right now...so I'm doing the control arms. I should be able to improve more than just the caster though. I should be able to improve the camber gain (dynamic), scrub radius, and roll center (eliminate any vertical or lateral movement of this during suspension travel). My main focus will probably be the caster and camber (both static and dynamic). Currently it calls for -1 to 1 deg of caster and 0.3 to 0.8 deg camber. I'd like to have a few degrees of caster and start with a slightly negative camber (so that when I turn a corner and there is camber "gain", I'm not much beyond 0). Once I get the coordinates into the software, I can easily make changes and find out what I can improve and how much. My dad and I started to measure all the coordinates last night, but got about 10% done and realized it was going to take a while. We decided to continue on Sat. It's going to be tough to get accurate numbers with everything fully assembled.

[dennis68]

I'm confused; do you want camber to move positive in bump? Most designs would gain negative at least 1* or so per inch of bump.

The only way caster can change is if there is deflection in the system. It is a static measurement based on camber at 10* of turn (at least this how I measure it with our Hunter P611). Even if you could measure it dynamically any change would be a result of other variables, not designed change.

How much camber do you think you are going to be able to "engineer" into just replacement arms in the stock locations?

I suppose you could reduce scrub radius by adding length to the arms and running different wheels.

How the hell are you going to eliminate RC migration by changing control arms???

Good for you, doing it on your own is always better than buying somebody else’s "snake oil".

BTW, wrong board for unsubstantiated claims. Way too many engineering and suspension experts around here for that. Big difference in “Hi, I'm new and trying to learn" and “Hi, I'm an expert and this is what I can do even if it defies the laws of physics".

[MrQuick]

ok ok, hey Den go easy on him, he's new!
2nd gens don't need a whole lot of changes to be a well behaved street/track car. I'd like to try or ride in a car with the ST arms. Like to see if it would make a substantial difference over a close to stock car with minor mods.
I say try 1 1/4" sway bar, better bushings , adjustable shocks, springs, a set of nice sticky tires, lighten the car abit , go hit the track and work from there. no need to redisign just yet.

[searly71]

You're right, I'm not going to gain a whole lot by replacing the arms. I don't expect any major changes in the handling. I'm just doing this because it's a fun car-related project and a good exercise in suspension design, CAD, FEA (finite element analysis--for stress), and manufacturing techniques.

And while I'm a newbie and suspension is probably the vehicle system I know the least about, there CAN be dynamic changes in caster. What you measure when you do an alignment is the unloaded caster--there are no loads other than weight and the reactions to this. If you could measure the caster while the car was turning a corner and pulling 1g, it would be different than what you measure during your alignments. If you don't believe me, download Perf. Trend's Susp. Analyzer demo (http://www.performancetrends.com/SuspAnzr.htm). Open up any vehicle (like the '01 vette), look at the static caster, input a roll, dive, or steering change, then look at the dynamic caster. This program even calculates the change for you. Look at the 'side view' to see the change visually.

As for the camber change, you're right, it should gain negative during bump. When I was talking about positive gain, I meant during turning (on a flat track, like a skidpad). A well-designed suspension will maintain almost 0 camber during turning, so that the tire's contact patch and traction is maximized.

As for the camber, I can just change the length of the upper arm, which relocates the upper ball joint. That's the same thing you're doing when you add or remove shims.

As for roll center migration, I'm still looking into that. I based those statements on what I read in Herb Adams' "Chassis Engineering". I'm not an expert, but he is.

[dennis68]

Actually I spend a great deal of time the rack and do load the chassis for evaluation.

Pulling 1g is pretty good feat, you think your gonna get that kind of results? I'd be real impressed.

A lot of the caster change you would see is a result of toe out on turns and deflection not designed caster gain.

How is turning on a flat track different than another type of driving as it relates to camber gain? I have never seen a chassis that can maintain absolute 0 camber through roll, do you know of one?

Did herb Adams state in his works that control arms design has a major impact on RC migration, I must have missed that chapter? I'll go home and read it again.

I may seem like an ass but I'm really being nice and attempting to figure out what information you used to draw these conclusions.

[yody]

no, actually your not being nice, go sit in the on the bad boy chair in the corner and put the dunce hat on. Then come back and play nice like all the other kids. Really though constructive critizism is a good thing, it will make you think harder and weed out some of the problems. Dennis had done his research already so i am sure he can provide you with some decent info.

[dennis68]

See you next month Yody.

[David Pozzi]

PHR is doing a feature buildup of a second gen. Has some great photos of the car cornering with stock suspension. Take a look at the photos and we can talk about them.

[Marcus SC&C]

Searly71, basically You`ll be unable to make any kind of meaningful change in the camber curves with UCAs. But you`ve got somewhat passable camber curves already. You can add some + static caster (say +4*) and you can shim to get it where it works best once they`re made and installed. Shortening the UCAs to gain - camber is okay but don`t get too carried away. It`s basically the same as adding shims. You`ll get a tiny little bit of camber curve change due to the shorter arms but not enough to make any practical difference. You`re right about the caster gain. 2nd gens actually have quite a bit because they have a lot of factory antisquat. I wouldn`t consider it a main design criteria though. Longer UCAs and LCAs to allow the use of say 4th gen F car wheels to improve the scrub radius would be pretty cool if you could pull it off. As for programes I use the full vehicle version of PT Suspension Analyzer and I`ve been very happy with it. It had a few bugs but they`re pretty good with patches and upgrades. Be VERY CAREFUL when entering #s BTW. All of these programs that I`ve used are prone to glitching and changing or transposing #s which can really ruin your day (or even month). I keep the graphic open all the time,the glitches are almost always instantly noticable. FWIW this program is one of the best in this regard so it doesn`t happen too often. Marcus SC&C

[searly71]

Thanks a lot Marcus, I appreciate it. When you said anti-squat, did you mean anti-dive? I thought squat was when the rear end shifts downward under hard acceleration? Yeah, the more I look at this, the more it seems the only thing I can substantially change is the caster. I think maybe I'll redo this design when I do a complete resto/mod and have the front of the car disassembled...wouldn't be too expensive to build them again. Once I get the software going I'll see what a shorter upper arm will do. I was thinkin about it and it is like adding shims, but with adding shims you are relocating the whole arm, so the mounting/pivot point changes. If you shorten the arm, the pivot point doesn't change. I'm glad to hear from someone who's used the software. Did you pay $400 for it (or whatever it is)? My demo expires soon and I don't want to spend that kinda cash for software...

David, what's PHR (sorry, I'm new, remember)?

Dennis, I guess we can both learn somethin from each other...
from Herb Adams (pg 48): "the roll center location can move both vertically and laterally if the upper control arm length is not correct"
I know I can't pull 1g...but some cars can...and the effect is the same for .1g. I specified a flat track just to keep things simple. And I know no car keeps the camber at 0, but that's the goal. I might be wrong, but I think some cars maintain less than +/- 2 deg throughout various steer, roll, and dives. If that's not "almost" 0 to you, I apologize. And I'm not trying to be an ass, but I am curious about some things: How do you load the car with such high forces? Just 0.1g's for a 3000lb car is 300lbs...that's a lot to test...how do you do it? Do you simulate roll, steer, and dive? What application are you doing this for, race cars? Also, how does the toe-out change the caster? I thought that would just rotate the spindle, not change the angle of it (change the position of the upper ball joint). I can't seem to visualize it...

[dennis68]

I have a winch (cable come along) that I attach to various places depending on the type of movement I need. Eyelets attached to the concrete, eyelets attached to rack itself or the opposite rack. Works great.

I deal with 1/10's of degrees all day so +/- 2* is huge to me.

I thought about it some more and camber gain has a lot to do with it as well. Since caster is a measurement of camber at specified turning degrees and toe has quite a bit of affect on camber it would also have an affect on caster.

To actually see it, find a good alignment guy and have him put a car on the rack with the toe zeroed. Run all the numbers then toe the wheels out 1/2" or whatever and re-run the numbers. There will be a substantial difference in every reading.

PHR is the acronym for Popular Hot Rodding-1 of the greatest P-T magazines in the world.

[Salt Racer]

Caster curve is a function of SVSA length. I'm guessing the reason why Dennis is not seeing caster change is he's pulling down only the front end. Resulting chassis rake will change caster reading on alignment machine.

It isn't really practical to regain camber lost due to roll via short FVSA only (decreased tire contact under braking, increased side scrub, jacking etc). It's possible to design caster curve to aid this. Prime example is factory geometry of C5/C6 IFS. However the amount of caster should be kept moderate unless you have very small scrub radius, as discussed in another thread.

PHR is doing a feature buildup of a second gen. Has some great photos of the car cornering with stock suspension. Take a look at the photos and we can talk about them.

The roll rate doesn't seem too bad considering massive tire roll over, though more than likely it'll be too soft when the car pulls higher lateral acceleration with sticky tires.

Braking pic suggests that either the car has massive static positive camber or suspension has very long FVSA. Front tires are near vertical even with fair amount of bump travel.

I just glanced at the magazine the other day so I have no further comments at this time.

[jeffandre]

PHR is doing a feature buildup of a second gen. Has some great photos of the car cornering with stock suspension. Take a look at the photos and we can talk about them.

David,
Is the Feature Buildup a 1-month deal or is it going to be spread over time? WHen did it come out (I can't find it in my town, will look elsewhere but may be too late)?

The reason I am asking is that I am close to tearing up my front end to check my static alignment settings and consider modifying the following:
1) UCA mounting locations (for camber/caster ranges I am after, similar to Ripper's Bird).
2) Longer upper ball joints.
3) And finally frame and sway bar mods to clear big tires.