Theory question- downsides to very aggressive camber gain?

[iadr]

Ignoring that some tires don't want or need a lot of camber gain, and that if you use stiff enough roll-resistance, that negates the need for camber gain- ignoring those aspects and focusing on the geometric end, how does too much camber gain make itself know in the front of a scratch built unequal length control arm front end?
Say Guldstand mod plus tall ball joints, but to make it fair, the bumpsteer isn't a problem, just that the wheel swings through major camber curve.

I poster on another forum, said: You're making the geometry approach that of a swing axle.

Ok, so...? Swing axles are bad, but... I guess why, in this case?

Basically I am trying to understand it, so any phrases you through at me, I'm going to google...

[MIKE67]

One problem is that under braking, the front of the car dives down, the tires lean in at the top and decreases the contact patch. Thereby reducing braking performance and increasing tire wear.

[parsonsj]

Braking is the most serious of the problems, but lots of camber gain can also cause side scrub where the wheel moves orthogonal to vehicle direction. Excessive side scrub can cause a reduced contact patch and all the problems that might entail.

[UMI Tech]

I love this question.

So, for an A-body GM vehicle, we can range from 0.5 deg/inch with a stock spindle to upwards of 1+ deg/inch with tall solutions.

Is 0.9 deg/inch to 1.1 deg/inch pretty reasonable?

ramey

[parsonsj]

When Katz designed II Much's front suspension, he tried to get about .6* / inch in street mode, and .9* / inch in track mode. (the suspension had dual mounting holes for the UCA). The tradeoff between the two was side scrub (don't remember the difference). I ended up leaving the car in track mode all the time, and found it to be dartier that way, though I got used to it. Toe was supposed the same in both configurations, though it's possible that it was different. (I used to do all my own alignments with string, a straight edge, and a digital level.)

Tire wear didn't seem to be much of a factor, and I really didn't notice any braking difference.

[SLO_Z28]

If you moved the upper control arms mounting point, you changed camber which would change toe. Toe out pre loads a tire and makes it more responsive/darty, toe in causes it to track better but be less responsive on turn in. You only need enough camber to keep the tire flat on turns, letting a tire roll positive is a bad thing. The camber gain on bump would allow you to run less static negative camber and help with your contact patch for braking. The amount of camber gain during bump that you want is entirely dependent on the car and the application.

[ace_xp2]

It can also lead to a lot of roll center migration, Whether or not that's always a bad thing I don't know, but I would think having the forces going from link to spring in a non linear manner is to be avoided.

[iadr]

OK, so for concerns,
- we have scrub (a specific type of),
- and we have contact patch during braking,
- and we have roll center migration. (And we have twitchiness, which may be more of an accidental by-product).

https://static1.pt-content.com/images/pt/2012/08/Miata__8707g-1.jpg

shows a Miata (yeah, don't laugh, they are supposed to handle very well.... Well it's really all they do do, so they better do that well....)
For those that don't know them, this is not a Mc-strut car, it does have UCA's.
So if handling was mostly in mind, why didn't they do a more aggressive camber gain?

It looks to me like it's set up with a bunch of static negative, and while the outer looks good enough, the inner is terrible. Yeah, not a lot of weight on the inner, but...might was well have it right, right? Until just now, I never noticed the rear is the same way...

Here's the stock version of what was my daily for many years (& yeah recently, not in the distance past):
https://static1.pt-content.com/images/pt/2012/08/544_autocross-1.jpg

And same thing with aftermarket roll bars, but modern tires so the roll isn't even that much reduced. (Neither pic is my exact car, btw)
https://static1.pt-content.com/images/pt/2012/08/544_51863921777-1.jpg

Subjectively, it is a nice handling car- good, fairly quick manual steering (box type), progressive & neutral loss of traction... The front end has UCA's, and the hardware has wide range of static adjustments, and an easy swap (performed) to very decent brakes exists. And, as you might guess from pic 2, the car has remarkable forward bite. Actually I have a bigger bar in fronn that he does, or that car is sliding the back end in the pic, or both.

but the limits are low.
I want to keep it restomodish, and don't want to throw the baby out with the bathwater.
I bought another full front crossmember to work on off the car, and want to reposition the UCA mount points..maybe lengthen the lower arms.
I mean, help me at least catch the low hanging fruit here, there is massive room for improvement... lol

[Twentyover]

Seems to me there are two features working against each other here, and possibly one is colluding with the other to keep overall grip low,

OK, first, does the suspension actually increase negative camber in bump? A bunch of old 'Murkin cars didn't, which is why taller spindles/relocated upper control locations proved to be such a revelation, By going from positive camber or no camber gain to negative camber gain in bump you at least don't have additive effects of camber change in roll.

The second effect, that i don't see so much discussion about, is camber change in roll, BZD above has what- 7 or 10 degrees body roll? That pushes the upper control arm outboard, and pulls the lower pivot inboard,jacking up positive camber. What I'll say next may be controversial, because it violates all the little crib notes people use.

Put a bigger front bar on it, or more front spring, or both. You'll reduce roll, which will reduce positive camber gain (total, not rate), This will let the front tires stay stuck a little better. Found this on the MG's We needed a LOT more front roll stiffness before a front and rear bar started working like we expected them to work. Addition of a front bar allowed improved front grip, because the tires weren't rolling into positive camber so badly. Once we started getting more even tire temps, we started trying to balance the back with the front.

Something to consider

[parsonsj]

The twitchiness on II Much with more side scrub is probably real. The toe was adjusted and checked after the switch from street to track mode. I was just disclosing that I did / do my own alignments, so there's no independent verification of my static settings.

On the photo of the Mazda, there isn't any conclusion you can draw about the unloaded inside tires -- they aren't exhibiting camber gain, they are nearly at full droop, etc.

[iadr]

- Yes, I do need to get the springs out of the second front end and do some sort of stand (couple milf, I mean milk, crates), and measure through the travel. I figure a digital angle cube on a wheel mounting surface should get me to a starting point of understanding...



On the photo of the Mazda, there isn't any conclusion you can draw about the unloaded inside tires -- they aren't exhibiting camber gain, they are nearly at full droop, etc.
Well my conclusion, or thought process,was
- outers are cambered well- at rest they would have a lot of static negative.
- inners are opposite to what is needed
- therefore the car has insufficient *gain* to keep the tires flat, and the appearance to me is that the car is running substantial static negative to "solve" that.
I had kind of taken gain to mean that in droop, we'd see a dropping down into a flat(er) contact position. Doesn't always work that way, of course.
- it has UCA's (Ie is not a strut design), and that makes me surprised they didn't "calibrate" the camber gain to be more aggressive, as the hardware is there to do so.

- it made me ask if there was a good reason OE designs use so little gain. One reason I thought of is for progressive/predicatable traction loss at the limits, for the average street driver.
- a poster on another board sated that the Solstice/Sky GM Miata competitor used much more aggressive camber gain. Let me go look and see if I can find the numbers...EDIT... NOPE...the dimension ratio of upper to lower arm length is 10.3:12.6 inches (Miata) to 14.2:8.3 inches(Solstice), so conclusions can to reached there, barring differences in how "level" the control arms each are...
- it should be noted in Mazda's defence that the early Miata's like the red car shown, were designed around a 185/60r14 tire, not the 255 or whatever is on that track car.

[parsonsj]

I had kind of taken gain to mean that in droop, we'd see a dropping down into a flat(er) contact position.No, it's the other direction: camber gain means that camber becomes more negative as the suspension travels in compression. That inside tire on the Mazda shows the suspension in droop (the opposite of compression) -- and so the camber "gain" is negative.

[iadr]

No, it's the other direction: camber gain means that camber becomes more negative as the suspension travels in compression. That inside tire on the Mazda shows the suspension in droop (the opposite of compression) -- and so the camber "gain" is negative.

Yeah, but.... if you have the upper arm's inner point much lower than the outer, then in cornering, not only do you get the dynamaic negative camber gain on the outside, but in droop your inside wheels get dynamic positive. Any time your camber curve crosses over (graphed), you are going to see some of this effect, I believe.
I kind of (so far, still learning this stuff) thought that was the classic ideal of double A arms...? Basically use the gain/loss to woggle the top of the tire in or out to keep the tire accurately perpendicular to the ground, or the contact patch parallel to the ground. Which ever way you word it, same thing.

Some Late 60's GM cars (Buick GSX's were mentioned to have this, so thats A bodies?), had front control arm instant centers outside (!) rather than inside the track. IE reverse gamber gain. They did this for a reason.... it's not like GM's engineers didn't know what the geometric result was... Greeks had that figured ~3k years ago. I believe I read a passing reference in a magazine to that being a dead end attempt at greater straight line stability?
Not really understanding why that would be.

[David Pozzi]

The Miata has fairly aggressive negative camber gain at around .7 degrees per inch, .7 to .8 is considered "ideal" from what I've heard. If you go for much more than that, the IC moves way more & so does the roll center. If the RC moves very high, you might experience jacking effects On flat or slightly off camber turns. Also when you accelerate out of a turn, the front rises and your tires can camber the wrong way.

[Marcus SC&C]

Iadr, awesome question, if a complicated one. "Ideal camber gain" varies widely from platform to platform. In a very nutshell the heavier a car is, the higher and farther forward it`s CG, the more narrow it`s track relative to it`s length, and so on the more the car will generally work better with more aggressive negative camber gain in bump. You can see this trend in modern performance cars, C6 Corvettes are fairly light,low,wide and very well balanced so they can run very little negative camber gain in bump and still have excellent grip. A new Camaro is fairly wide and decently balanced but it`s very heavy and tall so to achieve it`s best results it has nearly 3 times as much negative camber gain! This only works up to a point of course. As in all things suspension more is not always better, just right is always better. What is right for each car can be speculated with computer simulations etc. but only the real world performance of the car is definitive. Camber gain doesn`t exist in a vacume,it coexists with many other variables. Changes in spring rates, swaybars and even shock settings change the equation. Since geometry is typically hard to change we usually just change the static alignment settings to compensate. If we get too much of a good thing, such as running an A body with tall spindles AND tall ball joints together, there are numerous negative effects. As noted here, braking can suffer, roll center migration can go awry (although it was already really bad on those cars to begin with) and the uber high resulting roll center can cause excessive suspension jacking. This last effect is most easily felt in the rear suspension of old VW beetles. Their FVSA (front view swing arm length) length is very short causing the tires to tuck under when you corner hard,this lifts the outside corner of the car until the tire looses grip,then the car drops,gets some grip again and repeats in a cycle called porpoising. It`s scary when it happens on the rear of a 50hp VW ar 40mph. I do not want to experience it on the front of a 600hp PT car at 120mph! :eek: That said,some jacking effect is beneficial because it basically gives you more rate on the corner that needs it the most and only when it needs it. A higher roll center shortens the moment arm between the CG and RC which results in less leverage and less inherent body roll. So really it`s not just about camber gain, it`s finding a tricky balance of the camber gain the car works best ,along with the roll center height that works best, minimizing lateral roll center migration, optimizing FVSA length, eliminating bump steer etc. and then tuning the package properly for it`s application. Most cars in the size, weight and balance class of a typical muscle car, tuned for good handling on the street respond well to around -.7 degrees of negative camber gain off ride height. You`ll find most modern performance cars platforms in this general class will share similar numbers. No surprise since physics couldn`t care less what year a car was made. This rough amount of gain makes it easy to retain excellent drivability on the street and still achieve very good track performance with static alignment settings than won`t eat tires like candy.
In the pics with the Volvo (cool little cars BTW) you can see that the outside tire is trying to corner on the shoulder of the tire and isn`t making good use of the tires contact patch. Speaking in broad terms,you could dial more static negative camber in to reduce the effect but it will still roll just as much and street drivability and street tire life may be impaired. You can see that relative to the body the loaded outside tire is cambered out a bit at the top. That indicates some positive camber gain in bump and implies a roll center that`s quite low as well. Modifying the suspension to achieve more negative camber in bump would not only allow the tires to keep their contact patch on the pavement but would also raise the roll center and reduce body roll. This basically attacks the problem from both sides. It`s also fairly common to see an improvement in roll center stability which would make the car more predictable to drive. Sorry though, we don`t have any StreetComp kits for classic Volvos. :doh: :) Mark SC&C