Test Results: Guldstrand Mod

[TheBandit]

I took this data after talking with Marcus at SC&C. Over the phone he told me that the camber curves floating around on the Internet for the G-mod were wrong. I could only assume he was talking about David Pozzi's curves, but he didn't say. All he said was that more beyond the Guldstrand mod was needed to get to a modern camber curve. To paraphrase, "the Guldstrand mod only gets you halfway there." I was a little shaken by this contradiction, so I decided to test it myself.

Here are my results:

https://static1.pt-content.com/images/pt/2011/07/ly6swap175-1.jpg

This is as measured on my '70 Nova, completely stock except for the Guldstrand mod (via templates directly from D ick Guldstrand: you can see exactly how I did it here: https://www.pro-touring.com/showthread.php?78054-How-to-do-the-Guldstrand-mod-the-quot-hard-way-quot

Here is how I measured:
- digital angle finder (+/-0.1deg repetability) on the brake rotor
- tape measure to nearest 1/16th from the floor to a mark on the center of the wheel bearing cap
- cycle suspension with a jack, move to a new position and measure, repeat
- 0 determined by measuring the position where the LBJ is approximately 3/8" below the average position of the front and rear bolts of the LCA frame pivots
- data includes 3 cycles completely up and down with approximately even spacing between measurements to collect a locus of points
- max and min ride are where the bumpstops just made contact with the frame
- frame supported by jackstands, suspension assembled and tight, approximately steered straight

https://static1.pt-content.com/images/pt/2011/07/ly6swap173JPG-1.jpg

https://static1.pt-content.com/images/pt/2011/07/ly6swap174JPG-1.jpg

I have a significant portion of travel where the camber is relatively constant (between -1 and -3.5) and even hooks back a bit. What do you think of these results?

[Nessumsar]

The only problem I see there is your "0" setting. Putting the LBJ lower than the mean of the LCA pivots is far to high (car height). IIRC, typically with lowering springs the LBJ is about 1.5" higher than the LCA pivots. You may want to double check, but I would re-do the measurements with the LBJ higher at "0".

Otherwise, bravo.

[TheBandit]

Are you sure? If the LBJ were 1.5" above frame pivot, I would be against my bump stop at ride height. The 3/8" refers to the approximate center of rotation of the balljoint. I estimated this by eye to be close to inline with the top flat surface of the arm around the LBJ. The zero point on the ride scale can be shifted up & down to wherever you would expect the ride height to be, without effecting the curve. I don't know yet where my ride height will end up. I chose 3/8" because Marcus at SC&C recommended the LBJ be slightly below the frame pivots at ride height. I have read something similar elsewhere. I'm not sure where this "magic number" comes from. He told me this was to prevent the LCA from being at a transition angle at ride.

Did you take any data before & after your CR mod?

[Nessumsar]

Before we did the work on the front of my Nova, I had Hotchkis drop springs; and the contol arm was ~1/2"-9/16" off of the bump stop. You don't have much travel when lowered on the stock control arms (which is why most aftermarket LCA have more of a curve).

Marcus mentions having the LBJ lower (relative) than the LCA pivots so that when the suspension compresses, the LCA "grows" in length creating more negative camber; but in reality if you set the car up this way, it would be far too high.

We did take cycled-measurements before doing the CR, and IIRC we LOST camber. That was with stock upper and lower control arms and ball joints.

You could combine your Gulstrand mod with some tall LBJs to get the LCA more level at ride height; but this opens a whole nother can of worms in bumpsteer.

edit: I also think that we (this subframe people) need way more caster than we think. I would like to get into the 9* range of caster; maybe through the combination of geometry "corrected" lower and upper arms combined. Jason Rhodes is building a STX prepped 1st Gen Camaro, and has some really interest info posted on his site. This is the page on his suspension findings: http://www.rhoadescamaro.com/build/?cat=10

[David Pozzi]

The actual lower ball joint pivot point is right at the top side of the A arm. All of the camber tests seem to start at a different ride height.

My Camaro tests were on my 67, which used a template from Guldstrand that was a bit more aggressive than the one they give out now. Plus I later sectioned & lowered the whole mount & went back to the factory holes, but my lowering was not all that precise & I did want to create a little extra gain when I did it.

[jay72nova]

I realize it been over a months since this thread was active but what would the ideal camber curve look like for a nova/first gen camaro? I realize "it depends"and an agressive camber curve also negatively effects braking....but what is the ballpark we are looking at? one degree per inch?

Bandit, thanks for posting this it looks like it in the same ballpark as Mr Pozzi's graph... possibly a little more mild of a camber curve but not much.

and Mr Pozzi... what would you think about making spacers for where for the balljoints , mount to the spindle to "dial in" camber curves...I think its something I might try.

[David Pozzi]

.7 to .8 deg camber gain per inch of bump seems to be a ball park goal. There are circle track upper ball joint replacements that use spherical bearings & a separate stud with spacers that can be swapped around to change the camber curve.

[jay72nova]

ahh, thank you sir!, adjustability is good!!...I are there ones that have a baseline close to our stock height?..why don't more people user these, it would seem to solve alot of the problems associated with useing the 1 inch tall ball joints, doing a more agressive "gmod" etc.
What I was imaging in my head were cone shaped bushings that you could put in the spindle, when I look at the threads sticking out from my ball joints it looks like a I have a 1/2 inch to play with between both ball joints and still have threads sticking up over the nut, not much but enough to add couple tenths of a degree...maybe more like a 1/4 inch and still have room for thick c.pins but thats enough for 2/10's I would think.

[Marcus SC&C]

As I always say, the devil is in the details! I always qualify my statements but if you take them out of context you may have issues. Assuming is a dangerous thing to do, I didn`t specify any one set of camber measurments on the internet because there are many. Most were measured on a specific car (almost always a race car) with a non stock configuration so the numbers apply only to that single car, not your own car. The numbers are probably spot on for THAT car but you need to generate your own numbers to know where YOU stand. We`ve measured dozens of cars but each car and configuration is different. It`s just simple common sense.
The G mod was a method of tweaking the suspension in a way that tech officials wouldn`t notice. It worked after a fashion and that is why we sometimes still use it today. It is not without issues though. Lowering the UCA closer to the frame reduces droop travel dramatically. Not a huge deal on a race car but it is on a street car. Full bump travel is when the bump stop is fully compresed,not just when it touches. At or before full actual compression you`ll find that the upper ball joint is binding. You can see in the pics that it`s close to it now. When the car is together the fact that the upper A arms have swung not just up but also OUT in the arcs of motion will make aligning the car very challenging. A good performance alignment with stock arms and G mod is impossible on most cars.
The most common versions of the G mod drop the pivots about 3/4" (the more you drop it the more droop travel you lose and the harder it is to align with stock arms). The effect is almost identical to running a 3/4" taller spindle or upper ball joint. Except that the taller spindle or ball joint allows for more travel not less. A 1" taller ball joint or spindle adds about 25% more height increase with an accompanying improvent in camber gain and roll center height. All of the very successful tall spindles on the market today hover around 1.5" of additional height. That`s twice the height change of the average G mod and it`s MUCH more effective. You can`t get 100% as much gain from 50% of the change. There are no free lunches. To gain that much change with the G Mod we combine it with a taller upper ball joint, which lets us regain some lost droop travel.
There`s nothing wrong per se with the G mod, we still do it to cars in our shop once and a while where it`s applicable,mostly for vintage style race cars, we even have our own version but there are much better solutions today for a performance street car or PT car. Tall ball joints or tall spindles can achieve better geometry and performance while being simple and easy bolt ons.
There IS a reason more people don`t use mono ball style "ball joints". They typically have *half* the angular travel of a normal OE ball joints. They work fine on race cars with limited travel and aftermarket uppers with proper geometry but stock A arms have the wrong ball joint mounting plate angle to use them with modified geometry/lower ride heights and can cause them to run out of travel before the suspension does. When they run out of travel things break and cars crash. At the bump shown in the pics above (which doesn`t have the bumpstop compressed at all) a mono ball race joint would already have run out of travel. Even in the proper application they`re open to dirt and moisture and you can`t grease them. You may as well just get purpose built tall ball joints. We never use them for weight bearing lower joints lowers because their races have hardly any contact area for taking axial loads and they were out really fast. Contrast that with Howe tall ball joints, I have a set of lowers with way over 120,000 miles on them that are still showing no measurable wear!
It`s very cool that you`re doing your homework on the car but smart people have been modifying these cars for nearly half a century, all the easy fixes were figured out years ago. The industry,including us, are just "standing on the shoulders of giants" and refining those mods now. Keep you eye on the details like you are though and you`ll end up with one of the best performing cars out there. Mark SC&C

[jay72nova]

Thanks Mark I appreciate your input, as well as your clarification on using racing balljoints before I go looking for them to put on my car. I guess the answer is I need to measure my own cars camber curve before I do any more work on my camber curve.
I have a question for you...according to my calculations if i were to install a 1 inch taller balljoint in with my Gmod my camber curve would be something in the 1.4-1.8 degrees per inch? does that sound correct? and what do you guys think about how agressive that curve is?...
and please don't read me the wrong way, I am not trying to question your advice.. I am simply trying to flush out the numbers and opinions so I can set up my car. I'm not trying to start any arguments with people that know and practice this stuff in a league I am not in...I have never raced a car in my life...ski raced for ten years but you can adjust camber with your hips anytime you want on the snow:jump: drop those hips B!@#h
bandit I apologize if I am hijacking your thread at all.
jason

[Marcus SC&C]

Using a 1" taller ball joint with the G mod would result in an uber aggressive camber curve, way too much of a good thing. The RC ends up really high and the FVSA very short to the point where undesirable suspension jacking can occur. Much like the old ball joint extenders that stacked on on top of another. On a car with a mild drop (via springs/bags/CO not drop spindles) and a conservative G mod a +.5" UBJ works very well. Camber is only one aspect of the front suspension geometry. The combination that yields the "best" camber curve may not be a very good set up at all if the roll center is much to high, or low or if it has too much lateral migration, or if the FVSA is much too short etc. etc. It`s a somewhat complicated balancing act. Ride height makes a huge difference as to where in the curve the suspension is and due to the eliptical shape of the camber curves (which you can see nicely in Bandit`s diagram) how aggressive *that car* is with *that* curve. Camber gain that works well for a car at one height may be too much if that same car is lowered 2" more. A camber curve that`s too mild for a car at near stock height may be ideal for a car that`s slammed into the weeds when all of the pickup points move to a much more radical part of the curve. For those doing G Mod only, going aggressive with it (the original weld on method like Bandit did it is the cleanest way and can help some with getting a proper alignment if you move the perches a bit) and running the car as low as practically possible can yield good results (see above). Making the same change on an otherwise box stock car has it still in positive camber gain for the first inch or more of travel and neutral when it hits the bump stops with no negative camber gain at all because the UBJs pickup points are still lower than the cross shaft pickup points at ride height. It`s hard to make generalizations because we have to include every variable to make it even close to accurate. I try to make statements in reference an otherwise 100% stock system so there is a repeatable baseline, then discuss how other modifications may change things.
Basically as David said earlier, on this configuration of car we`re generally looking for between -.65 to -.80 degrees per inch right off ride height. It will get more aggressive as it goes. RC heights between 2" and 3" above the ground generally work out well as long as they`re also very stable. As cars get lower they loose bump travel and have less inches of camber gain to hit their end goal so gain needs to be more aggressive or the static alignment needs to be. Cars with milder geometry can still perform well if they run very aggressive static alignment but they may have more issues with tire wear and drivability on the street. There are no magic bullets or blanket solutions for all cars. That`s why I wrote my book, to give people a better feel for what`s involved in making THEIR car work the way they want it to. Mark SC&C

[jay72nova]

Mark I bought your book and have read it about 4 times, thanks for writing it!...ahh, .5 inch taller...for some reason I had it in my head that the standard taller balljoints people were using were an inch....maybe thats from all the second gen camaro stuff I have been reading that has me mixed up.. half inch, much better, I don't know how I missed it!

[exwestracer]

Using a 1" taller ball joint with the G mod would result in an uber aggressive camber curve, way too much of a good thing. The RC ends up really high and the FVSA very short to the point where undesirable suspension jacking can occur. Much like the old ball joint extenders that stacked on on top of another. On a car with a mild drop (via springs/bags/CO not drop spindles) and a conservative G mod a +.5" UBJ works very well. Camber is only one aspect of the front suspension geometry. The combination that yields the "best" camber curve may not be a very good set up at all if the roll center is much to high, or low or if it has too much lateral migration, or if the FVSA is much too short etc. etc. It`s a somewhat complicated balancing act... Mark SC&C

Mark,
You are SO right about the "standing on shoulders of giants"... Mark Donohue published this same information in "The Unfair Advantage" as it applied to the first gen Camaros they were running in Trans Am. The info is out there, you just have to know where to find it...

[jay72nova]

Mark,
You are SO right about the "standing on shoulders of giants"... Mark Donohue published this same information in "The Unfair Advantage" as it applied to the first gen Camaros they were running in Trans Am. The info is out there, you just have to know where to find it...

knowing where to find it, as well as WHO to listen to, is important...I know from ski racing, building motorcycles and my proffession that there are allot of people who will offer advise and even publish books ..and even be instructors ....that really have no clue what they are talking about...I don't know how many times I have sat on a chair lift and listened to some "expert skiier" offer advise on how to ski that was just plain wrong...horrible backwards advise that might give short term benefits but mess up your fundementals... ski instructors with certification pins and mountain jacket can be the worst.... to thier defense they were taught a style that was not what is taught in racing...but its still BAD to slide on ice and then get thrown when hit you hit something soft because your fundemental dynamics are just plain wrong the fundementals that keep you stable at 80 on the downhill course keep you stable putting down the bunny slope....and then when you add the changes in technololgy to things...everything is further complicated so for exemple in the day of stiff straight racing skiis you had to PRESS the shovel of the ski hard and early to initiated the turn...if I ski like that now I litterally crush most skiis so that they fold under me because skiis are constructed differently than they used to be...so you can read a book on the fundelments of ski racing dynamics that was published in 1995 or listen to a guy who won his last race in 95 and you'll be initiating turns in a way that does not apply since they shortened softened and shaped skiis...
and so for people like me who havent been car racing and building cars with the "best of em" it can be really difficult to wade through the BS and find people you can really listen to...especailly when there are products being sold and promoted...technology is constantly changing and you are new to the sport. (by the way in my unqualified opinion I am not suggesting any of this applies to people on this thread)

[exwestracer]

knowing where to find it, as well as WHO to listen to, is important...I know from ski racing, building motorcycles and my proffession that there are allot of people who will offer advise and even publish books ..and even be instructors ....that really have no clue what they are talking about...I don't know how many times I have sat on a chair lift and listened to some "expert skiier" offer advise on how to ski that was just plain wrong...horrible backwards advise that might give short term benefits but mess up your fundementals... ski instructors with certification pins and mountain jacket can be the worst.... to thier defense they were taught a style that was not what is taught in racing...but its still BAD to slide on ice and then get thrown when hit you hit something soft because your fundemental dynamics are just plain wrong the fundementals that keep you stable at 80 on the downhill course keep you stable putting down the bunny slope....and then when you add the changes in technololgy to things...everything is further complicated so for exemple in the day of stiff straight racing skiis you had to PRESS the shovel of the ski hard and early to initiated the turn...if I ski like that now I litterally crush most skiis so that they fold under me because skiis are constructed differently than they used to be...so you can read a book on the fundelments of ski racing dynamics that was published in 1995 or listen to a guy who won his last race in 95 and you'll be initiating turns in a way that does not apply since they shortened softened and shaped skiis...
and so for people like me who havent been car racing and building cars with the "best of em" it can be really difficult to wade through the BS and find people you can really listen to...especailly when there are products being sold and promoted...technology is constantly changing and you are new to the sport. (by the way in my unqualified opinion I am not suggesting any of this applies to people on this thread)

Jay,
If you haven't read "The Unfair Advantage", DO SO. Not only is it a great story, but there is a ton of great info about how suspensions work and how to make them better. Keep in mind Donohue was an engineer as well as a racer, and a lot of the ideas he pioneered are still in use throughout racing today. Definitely NOT BS...

[jay72nova]

thanks Ray!!, I just ordered it!!

[TheBandit]

Marcus and all, I'm glad you're chiming in because that was really the point of the thread - to get a good technical understanding of this thing and try to understand the results. I realize this is only a small piece of the whole puzzle and there are many things to consider.


The G mod ... is not without issues though. Lowering the UCA closer to the frame reduces droop travel dramatically.

I've heard this several times, but I don't understand the argument. I measured my G-mod templates to lower the frame pivot by about 7/8". The control arm is about 9" from pivot to UBJ and about 6" from pivot to droop stop. Based on the arm ratio, the 7/8" movement at the pivot would reduce the droop travel by only 7/16". That doesn't seem dramatic to me. When you lower a car, more of the droop travel is available from ride height, so in a sense I am not really losing anything. What am I missing? Ball joint considerations?

BTW, I am still strongly considering your lightweight adjustable arms, but don't think I will swap in taller ball joints at this time. My curve shows around -0.5*/in of camber gain at ride, which while not as much as the ~-.65-.8*/in targets you mention, does seem like a good starting point. The cost of taller joints isn't prohibitive for me, but I have other areas I need to spend the money to balance out other suspension aspects of the car (subframe connectors, rear springs, rear swaybar, etc). I finally ordered your book along with the Donohue book that I didn't realize had gone back into print. VERY COOL!

[jay72nova]

I havent received my Donohue book yet...but I did get my "race car engineering and mechanics" book I think its by the same guy...Paul Van Valkenburgh...so far the chapter on tires is really good, I hadnt thought about keeping the tires on the edge of the friction circle...at thier friction limits at all times to keep the suspension smooth and settled...Im not sure how thats possible but its sounds good.

[TheBandit]

Marcus, any response regarding the travel reduction?

[79-TA]

I havent received my Donohue book yet...but I did get my "race car engineering and mechanics" book I think its by the same guy...Paul Van Valkenburgh...so far the chapter on tires is really good, I hadnt thought about keeping the tires on the edge of the friction circle...at thier friction limits at all times to keep the suspension smooth and settled...Im not sure how thats possible but its sounds good.

That's a GREAT book. Paul is a really knowledgeable and nice guy. In the book, he references many of the Caroll Smith books which would also be good to look into.

[TheBandit]

I havent received my Donohue book yet...

I have been hooked on mine since I got it. I'm about half way through now. It's not a technical book at all, but an incredible slice of history with great story telling.

[UMI Tech]

:cool:I grew up reading Carroll Smith's books as well. Along with Van Valkenburg's, and The Unfair Advantage, you can really get a good feel for what they went through "back in the day" to make cars fast. All these books teach you to think.

[exwestracer]

I have been hooked on mine since I got it. I'm about half way through now. It's not a technical book at all, but an incredible slice of history with great story telling.

Actually, it's VERY technical in many aspects...you just don't get to that until about the 3rd read...:)

[jay72nova]

I have been hooked on mine since I got it. I'm about half way through now. It's not a technical book at all, but an incredible slice of history with great story telling.
Yup good book!, I'm almost done(with my first read at least) its been good. Though there arent hard numbers he constantly is talking about how he goes about setting up the cars he is racing.