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Silwer: Natuke madal...

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rustang:

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Raceboy: kere jõuõlg käändtelje (ratta) suhtes suureneb ja tulemuseks on kere suurem kaldumine kurvis.

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Seda väidet ei hammusta lahti....

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The tendancy of a car to lean is determined not by how far the
CG is above the ground, but how far the CG is from the roll center.
That is a simple statement of fact. Look it up, if you don't believe me.

Here's the problem. When you lower a car with MacPherson struts (our cars)
the roll center lowers farther/faster than the CG. So if at the stock height the
roll center is 4 inches below the CG, when you lower the car 2" the CG
drops 2" but the roll center drops say 6". The actual tendancy of the car
to lean during cornering then increases. To counter that tendency you need
MUCH larger springs. Not namby pamby 300-400lb springs but
500-600lb race springs. Are you willing to run 500lb springs on
your street car?

The reason MacPherson strut equipped cars have this problem is
because the angle of the lower A-arm relative to the chassis changes
as you lower the car. Lower too far and the arm tilts
the wrong way, lower on the chassis side and higher on the strut side
and the rolling of the car has a greater mechanical advantage on the
strut causing it to compress the spring easier as the weight
shifts to the outside. That change in geometry is what changes the
roll center.

It has other negative side effects too. At the stock height, the
lower A-arm is higher on the chassis side, and lower at the hub.
When the suspension compresses under cornering the arm moves
both up toward parallel with the ground, and because it pivots
on the car side, the outside end moves out a little as well. That changes
the angle of the strut itself pushing the bottom out, causing a bit of added
negative camber relative to the static position. That is a good thing,
especially for our front heavy cars.
You want the added negative camber to give you better laterally grip
as the car leans and as the tire sidewalls roll over a bit. (Race tires
can compensate for decreased negative camber by having stiffer/higher outter
sidewalls.. see R1s.. )

As you lower the car moderately the A-arm starts out parallel to the ground
and now with suspension compression during cornering, the arm swings
through the part of the arc where there is no change in camber. That'd
be fine if you could totally eliminate body lean while still having usable
suspension travel (you can do this with a double A-arm suspension but not
with a MacPherson strut). But because you're lowered, you're eating up
your suspension travel and are liable to run into the bump stops at which
point your suspension STOPS WORKING completely.. You're no longer
"suspended".

If you continue to lower, you experience the problems above, but
in addition now the A-arm is above parallel so you have to dial in
lots of static negative camber, and ANY suspension compression causes
the arm to swing up and back inward tilting the bottom of the strut inward
as well causing a positive camber change. A positive camber change
during hard cornering is *NEVER* desirable. The tire is leaning
the wrong way. So add it all up; the roll center lowers faster
than the CG, so the car actually wants to lean more, you have less
suspension travel so that lean causes you to come down on the bump
stops causing instantaneous weight transfer, and you push into positive
camber, all of which decreases your lateral grip, sometimes suddenly.

There is actually a way to fix a lot of these problems, and it's
called a drop spindle. Basically you drop the car with springs, decreasing
the distance from strut top to wheel, but then the hub has a lower A-arm
attachment point that sticks down below normal. That allows
the actual geometry of the strut and lower A-arm to remain the same
but the car to sit lower. Another way to picture it is if you leave
the stock looking strut in place, and simply moved the hub
that the wheel attaches to upwards. That lowers the car keeping
everything else the same.
The bad news.. They don't make drop spindles for our cars. Period.

Lowering an 25-35mm (1-1.5") won't cause great harm (1.5 is pushing it).
Going below that is for looks only unless you're running on a race track with
3 degrees of static negative camber, 500 lb springs and race rubber.

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