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.
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To fix our roll center and camber curve we got all the right parts right out of Ford Racing competition parts catalog. The Ford system is the most well engineered set up we have seen and is straight off of the Boss 302R Grand Am Continental race car. The system starts with new lower control arms that have a special ball joint with a longer shank. This effectively lowers the lower control arm pivot to around where it was at stock ride height restoring the roll center to around the stock location. This also reduces the overall roll couple and fixes the camber curve. The control arm also includes special hard urethane bushings getting rid of the large, highly compliant lower control arm bushings.
You can see that the longer shank drops the pivot point by about 1.5″. The ball joint mounting boss angle has also been changed to reflect the longer shank and to prevent binding.
The control arms have a zerk fitting so the bushings can be fed with grease without disassembling the front suspension.
The rear of the control arm has a pivot. The pivot on the arm remains stock but the frame side is very different than stock.
