MKII Suspension Analysis: Front Suspension

Finally got arround to modeling up the front suspension on the MKII in optimum K. The analysis and discussion for the rear suspension can be found in this thread

As before, it is based on my own measurements of my car with Tien S-tech springs, which lower 1.5" according to Tien. Stock is based on raising the car 1.5" from what I measured. Green = stock, red = lowered 1.5", and Blue = Lowered 1". As before, body roll is to the right, aka car is in a left hand turn, so the right is the outside wheel, should be the dashed line in the graphs. As with the rear analysis the choppy parts of the graphs are due to the program not knowing how to handle excessive roll center migration.

First, the graphs.

Roll vs camber:


Roll vs Toe:


Roll vs Roll center migration:


Roll vs Spring Displacement:


The first thing I noticed with the front is that lowering it actually REDUCES roll center movement compared to stock. This I found to be very strange, but as far as I can tell my model is fairly accurate. I'm really not sure what is so different about the front geometry that this occures. One thing not shown on any of the graphs is the actual location of the roll center. Stock it is about 1" above ground level and when lowered 1.5" it is about 3" below ground level, so you can see how it drops siginificantly more than the CG when you lower.

Another interesting thing about the roll center. Stock, it moves toware the inside of the turn. When lowered it doesnt move as far, but it now moves toward the outside of the turn.

The other strange thing is that it APPEARS from these graphs that if your going to lower the front you are better off lowering it more rather than less. Dropping it 1.5" seems to have a better effect on roll stiffness and roll center movement than does lowering only 1".

The front seems to experiences a reduction in roll stiffness when lowered, just like the rear. However, it doesnt appear to be quite as severe, and in fact the spring displacement vs roll becomes very linear when you drop the front 1.5", compared to the rear where it was linear stock.

As with the rear, lowering has a slight negative impact on the camber curves.

The front appears to toe in the direction of the turn, and lowering only increases this tendency. Not a big deal either way in my opinion.

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Now a bit of analysis of the front and rear at the same time, Roll center migration:


This is where things get a bit crazy. As you can see, at stock height the front roll (Solid Line) center moves quite a lot, the rear (Dashed Line) hardly moves at all, and both move toward the inside of the turn.

Lower it 1" and now the rear moves a lot and the front moves a little. The rear is still moving into the turn, but the front is now moving OUT of the turn.

Lower it even more and now they are atleast moving in the same direction, rear still moving a lot, front moving not quite so much.

Now, if this is right this will cause the roll axis to swing out in the rear and stay centered in the front when lowered. This should tend to cause the rear to lift (due to roll) when lowered, increasing oversteer. Stock the front swings out and the rear stays centered, which should lift the front, reducing oversteer. Sound right?