Suspension testing.
11-11-2003, 10:00 AM
#11
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Join Date: Dec 2002
Location: Salem, MA
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Vehicle: 2K Tib
Here what I think based on my performance driving experience (autocross and track)
The current suspension setup is designed more for highway speeds. I found the car easier to maneuver and control at speeds above 60 than below 40. Generally, The cars balance is very good and well designed. The wedge is zero and remains so even with differential weight in the front seats. The car is easily controlled within it's design limits and recovers easily in either understeer or oversteer conditions.
The car is too softly sprung. Stock spring rates are ~225 lb/in front and 90~100 lb/in rear. The weight proportion of the car is 63/37 front bias but the wheel rates don't match up (this is how they engineer in understeer). To balance the car with a 225 front spring, the rear rate would have to go up to ~140. However, the front springs are themselves too soft for performance driving and should be (in my opinion) something like 300-350 lb/in.
Stock damping rates are inadequate for performance driving or to match with performance springs. The are valved to handle only the stock spring rates in "normal" driving conditions. In any performance driving condition (or emergency condition on the highway) they are not capable of damping the dramtic dive/lift/roll of the rather stiff chassis on top of the springs. Of course, the soft springs and inadequate damping create a syngery effect.
Anti-roll bars. To me these are a fine tuning device and not the major suspension component. Changing the bars without changing the springs (or at least the dampers) is a bandaid for the larger problems mentioned above. I realize this is a suspesion tuning philosophy (i.e. stiff spring soft bars) there are others who argue the other way.
Alignment. Stock alignment is set up for "safety" (read: understeer) and tire life. Adding 1.5 degrees of camber on the front with no other changes makes the car almost completely neutral. You are going to pick up a little camber front and rear with the eibach lowering springs, you may want to consider decreasing the rear camber rather than increasing the front.
I can't think of anything else at the moment.
The current suspension setup is designed more for highway speeds. I found the car easier to maneuver and control at speeds above 60 than below 40. Generally, The cars balance is very good and well designed. The wedge is zero and remains so even with differential weight in the front seats. The car is easily controlled within it's design limits and recovers easily in either understeer or oversteer conditions.
The car is too softly sprung. Stock spring rates are ~225 lb/in front and 90~100 lb/in rear. The weight proportion of the car is 63/37 front bias but the wheel rates don't match up (this is how they engineer in understeer). To balance the car with a 225 front spring, the rear rate would have to go up to ~140. However, the front springs are themselves too soft for performance driving and should be (in my opinion) something like 300-350 lb/in.
Stock damping rates are inadequate for performance driving or to match with performance springs. The are valved to handle only the stock spring rates in "normal" driving conditions. In any performance driving condition (or emergency condition on the highway) they are not capable of damping the dramtic dive/lift/roll of the rather stiff chassis on top of the springs. Of course, the soft springs and inadequate damping create a syngery effect.
Anti-roll bars. To me these are a fine tuning device and not the major suspension component. Changing the bars without changing the springs (or at least the dampers) is a bandaid for the larger problems mentioned above. I realize this is a suspesion tuning philosophy (i.e. stiff spring soft bars) there are others who argue the other way.
Alignment. Stock alignment is set up for "safety" (read: understeer) and tire life. Adding 1.5 degrees of camber on the front with no other changes makes the car almost completely neutral. You are going to pick up a little camber front and rear with the eibach lowering springs, you may want to consider decreasing the rear camber rather than increasing the front.
I can't think of anything else at the moment.
