RED_DRAGON_85

after reading a bit about suspension geometry, especially front geometry in a macpherson strut type suspension (the type we were blessed with) i have a question.

herb adams says that one of the main reasons race cars dont use macpherson strut suspensions is that they dont have enough camber gain in roll.
so i started thinking...
if you lengthen the a arm by two inches, so that the ball joint is two inches farther out, you will give the strut a higher angle relative to the a arm.
this will increase your camber gain in roll.

now i know you are thinking, "but hey dummy, if you increase the a-arm length by two inches, your wheel will stick two inches further out" which is why you would use 4th gen or camaro wheels. they have two inches more backspace than 3rd gen wheels.
which makes sense when you think about it because what GM did with the 4th gen was put the ball joint right in the middle of the wheel's width.

is there any reason why maybe nobody does this?
if there is something i am missing, feel free to point it out.
the only downside i see is that you would have to change the spindle to get rid of the extra negative camber you would induce.
lets get this discussion going

gregsz-28

iTrader: (1)

Start reading at post #38
https://www.thirdgen.org/forums/susp...o-project.html

You probably wouldn't have to modify the spindle, since you can adjust the upper strut mounts, and for more adjustment you can lengthen the camber adjustment slots on the upper strut mount. But even after doing that, you probably wouldn't be able to compensate for at least a few degrees of the added camber.

RED_DRAGON_85

if you move the struts out, you lose any added strut angle and benifit of lengthening the arm...

???

iTrader: (5)

i saw in another thread where someone said the 1st gen control arms fit and are 1in longer to the ball joint. but the stock ball joint won't work, as well as the spring perch. also the tie rods would need to be made longer too.


lots of work, not sure if it will make much diff unless your racing, but i don't think most classes allow mods like that. but i could be wrong.

RED_DRAGON_85

yeah, i guess it would have to be one of those things that you would have to make squeak by if your class didn't allow it.
i don't race at all but suspension geometry fascinates me...

Guest

Your thought is unfortunately way off base. I encourage your enthusiasm on learning geomertry so let my try and explain this Herb Adams quote better to you what is being talked about.

Your thought is based on static camber (stagnant ride height and no motion or body roll), where as Herb Adams is addressing the change from static to dynamic camber gain/orloss in relation to the cars tire footprint when body roll is induced.

You are basically trying to start your static camber at a higher negative footprint (in other words, ridng more on the inside edge of the tire) so that when the car body rolls laterally the tire stays flat to the ground. Good for the corner, but bad for the straightline- you wear the inside edges of the front tires severely.

Why is camber gain necessary in suspension articulation? let me give you a clear image.

At stagnant or motionless ride height, you basically want the tires to have a flat footprint on the ground for most traction down a straight path for both acceleration of the rear tires, and for braking footprints of all 4 tires. the most flat footprint, the most traction....point blank. No one can argie this fact, it is the law of physics.

So now, here lays the problem. You take that same car and load weight onto it laterally (from the side like centrifical force exereted in cornering) and that tires outside edges of the direcion of cornering will roll under leaving the tire footprints no longer flat for max traction.

Also, the same doubles when you merely jack up one side of the car (lets say the left side) 6 inches off the ground and look at the tire footprint on the opposite (right) side is now on the outer edges (also no longer flat for max traction). This simulates dynamic body roll "partially". I say partially because it does not truely represent outside suspension squat induced under lateral cornering loads. Squat would respresent suspension articulation. Its that very suspension articulation that you need to increase negative camber to "counter act the loos of camber footprint created by body roll. This camber curve, or geomerty incease is what is needed in suspension design to keep the tire footprint flat staitcally in a straight line and then also dynamically in corner loads with suspension geomerty change combined with body roll factor.

RED_DRAGON_85

i think you may have misunderstood my proposition.
lengthen the a-arm, while keeping static camber the same.
this will increase camber gain, as far as i know

Guest

(continued).......When you merely add 2 inches of length to the lower arm, you are just slightly slowing down the articulation swing and angle loss. You are barely promoting any less loss in camber gain (don't get me wront, a longer arm is good for this point) but are far creating bigger problems with leverage (changes spring rate affectiveness, you now need higher spring rates) as well as severely affecting unspeung weight through articulation.

So in other words, you gain one step and loose about 5 steps in other factors.

I have so many thoughts to try and type here it will just take one novel after the next in best angles for macpherson struts, as well as how ands why double arm suspension have gain in compression, but also loss in rebound when inside corner tire traction is availiable. Macpherson strut front suspensions are good when you can limit the roll weight and overall travel of the suspension so as not to have much articulatulation. Its why the little 60*V6 Camaro I built handled so well as opposed to the greater articulation changes you are faced with the heavier nosed V8 3rd gens. Its all in the macpherson strut suspension and chassis weights.

Dean

Guest

That drastically depends solely on your ride height and the a-arm angle starting point in articulation

Keep in mind-

A shorter arm will increase more when coming up to middle arch.
A longer arm will decrease less when passing over the articulation middle arch inverted. This is most likely what you will result in if your car is lowered slightly and you induce corner squat as well.

There is a limited range. Short and 'not inverted ever' in articulation is best desireable on a Macpherson strut suspension for camber gains.

Norm Peterson

When you change the rate of camber gain, you throw the bumpsteer off from whatever was OE. It might be an improvement, or it could make things worse. But plan on the possibility of having to correct it, and expect the inner tie rod pivot locations to not be quite where you want them to be.


Norm

RED_DRAGON_85

i really wish i had the means and time to experiment with all this stuff....
if you get into it, suspension theory is truly fascinating.