Now from what i've found with the front suspension, lowering it too much past 'centre' destroys the handling. Here's what i mean, this is arch gap of my car with 195/45/13's on 8j wheels.
Now i think it looks awesome, however look underneath and it looks like this:
Now as you can see the lower arms aren't exactly in the best shape or angle. This is the problem with lowering the car too much, now if you already know this, feel free to correct me/make it far more understandable etc etc this is purely because i always have people asking me how low my car was, and then ask why when i say, "looks cool, handles like crap". So the problem is when it comes to setting the suspension angles, and how they perform on the road.
To understand you have understand how with the lower arm in a fixed position on one end, and attached to the suspension at the other, when the strut moves up and down, because the lower arm is fixed at the other end, the suspension moves up and down in an arc. Now if the lower arm was parallel so the mounting points (one being the bolt in the subframe, and the other being the ball joint under the strut) if these two points were parallel and in line with each other along the horizontal axis, at this point the end of the lower arm, or the strut is at its furthest point in the arc, as soon the lower arm moves up or down (rotating around the pivot point where its attached to the subframe) it starts to move back on itself as such. This also works if you were to leave the suspension, and move the subframe up and down, from parallel, as the subframe moves down, the inner end of the lower arms would move down, and the lower arms would be point upwards towards the lower ball joints.
So now with that in mind, when it comes to set-up, forgetting the top mounts at the moment, if you wanted to incease the negative camber on the front wheels, you would simply make the lower arm longer, this would in turn 'push' the bottom of the strut outwards giving you the camber. This is where the problem revolves with regards to lowering your car too much, my car was lowered on coilovers (so i could litterally stick it on the deck) and as you can see in the pictures the lower arms are, when its sitting static, already in an angled position upwards. Now this is the reason, even with my camber top mounts set to max, i could still only achieve just under a degree of camber on the front wheels, not good!
Now if you think of this while driving along, tearing through those country roads, as you do
come up to a tight corner, on the brakes, now even with the 400lbs front springs i had, the front of the car would still dive (to put it into perspective, our race car will be running at the class weight of 945kg, same as a volvo! and were looking upwards of 800lbs, nearly a 1000lbs front springs, because race car! haha it will be running some serious rubber on the front however). Now when the front dives, the subframe dives and moves towards the ground, this in turn pulls the inner pivot of the lower arms towards the ground. Now this is where the magic happens, to start off with, as my set-up was already badly angled, when the subframe dropped it pulled the bottom of the struts in even further, as the ball joints were effectively travelling even further round in the 'arc'. Because it was pulling the struts in, (in drastic terms) this pulled the wheels onto positive camber, which is definately not what you want under braking. So this means you have to brake sooner and lighter, to slow the car down gradually as the wheels will just lock up through lack of grip if you brake late. So time is lost there. Now you've slowed the car down for the corner, you've got to go through it. More badness coming here. So the your going through a left hander, all the weight shifts to the right handside of the car. This transfer of weight, makes the car lean on the right side, the right side of the car lowers down on the suspension, the subframe once again moves down towards the floor, thus once again, it pulls the bottom of the strut intowards the car, here comes the positive camber! and the following understeer puts you on the otherside of the road... So you have to slow down so to not lock up on the way in, you cant corner as hard due to the understeer that will become of it. Its a set-up full of slowness. The car may look good slammed on the ground, but it wont corner!
So, this is what you want, ideally you want the car with the arms just above parallel. If you have them parallel the car will still pull them in under hard braking and cornering pulling off camber and moving towards positive camber. Now if you want them with the lower arms angled slightly, how much i dont know, you want the end at the subframe higher than the ball joint end. This will then cause the lower arms to "drop onto parallel" under hard braking and cornering. This in turn will push the bottom of the strut out for braking and cornering giving even more negative camber. This isnt ideal with regards to the braking as you are still not using all the width of the tread, however its better than positive camber under braking, and far better during cornering as you've got the camber for the car to 'lean onto' giving better cornering grip, thus better cornering speeds
When it comes to running camber on a car, its always a compromise between braking grip and cornering grip so you have to find the inbetween To get the lower arms in the correct position and still run the car low? Ideally you want to run the car lower to the ground for centre of gravity reasons and less force on the car trying to making it 'roll onto the outside wheel -the inside wheel still has grip too! So you can run 15s, so visually you'll have a smaller arch gap, you'll also be able to run wider rubber for better grip and you get better mpg. If you want to run 13's then you need to do some modifications. You can either lower the ball joint end of the lower arm down, however this will bring it lower to the ground and more likely to hit something if your as low as i was, or you can move the pivot point of the inner ends of the lower arms up, simply by re drilling the hole. Out of the two i'd choose the later. On our race car that Gartrac set-up back in 1990 odd, to sort this problem, they used rose joints on the lower arms (its a fiat 131 however the principle still applies) and then used a longer bolt, and a spacer to space the lower arm down to the correct angle. Being Gartrac and anyone that knows, knows Gartracs work is top shelf stuff, some of their work is awesome and they definitely know what there doing. However this moves the lower arm down making it more susceptible to damage as your running the car so low on the road. So i think the best way to do this is to raise the pivot point in the subframe. You do run into problems such as running out of room for the arms to move, or maybe not being able to move it up high enough, however it can be achieved by cutting 'the roof' as it were of the tunnel that the lower arms mount into, and welding in new sides the travel from the original 'tunnel' and up to the higher part of the subframe. Then re-drill the holes so the lower arms are positioned correctly.
Well its lengthy, but this is based on my experiences with the 300's and the racecars i've grown up around, thats my 2p, more like a few quid!, on how to set-up the front suspension for better braking and cornering ability. Just like you would if it was a race car
The amount of times i've come up to a corner and you can hear the outside wheels fighting for all its worth and the understeer, its just appauling, oversteer i can handle, but understeer is my one big bug bear haha. Well, i hope this makes some sense and can be of help I was heading towards sorting it however things changed and i now own a lada, which is even harder to get this sorted with its double wishbones, as i've got two arms that need sorting now! haha but hey ho i'll sort it Thanks, Thomas...............
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