Project Mustang 5.0 (White)- Reducing Understeer with Ford Racing
The McPherson strut suspension found in our Mustang has some good and bad points. The good points are that it is simple, lightweight, inexpensive to produce and takes up minimal space in the car. This in turn allows room for more narrow shock towers so the wider DOHC Coyote engine can fit. The bad points are few but perhaps the worse is that strut type suspension has some compromises when it comes to geometry, particularly when lowered.
Strut type suspensions tend to have the roll center (Geometric point in space that the car rolls about in cornering) drop rapidly as the car is lowered. A lower roll center can mean that the roll couple gets longer which increases the cars tendency to roll while cornering, all other things being equal. (The roll couple, in a very general and simplified explanation, is the distance from the roll center to the center of gravity, the longer the roll couple the more of a lever arm centrifugal force has to make the car roll over in a turn).
Strut suspensions also tend to lose negative camber under roll when the angle of the strut axis to the lower control arm gets greater than 90 degrees, common in a lowered strut car. This causes the camber to become more positive as the car leans over in a turn, exactly the opposite of what you want to maintain a good tire contact patch and maximize front grip.
So the benefits of lowering a car can be nullified in a strut car if the car is lowered by more than just a little. Often lowering a strut equipped car makes the car handle worse, particularity in the front of a strut equipped car where over lowering manifests itself as increased understeer. To fix this, some lucky owners of cars where there is a nice aftermarket have off the shelf aftermarket solutions to fix the front suspension geometry. If you are a Mustang owner you are in luck as Ford Racing has a well engineered geometry correction solution for you right off the shelf.