Weight bias is the proportion of weight distributed between the front and rear of the car. A perfect weight bias is 50/50. With a front-engined car such as a Mustang, a 50/50 weight bias is possible, but it's difficult to achieve given the weight of the engine hanging over the front wheels. Even the race-bred 2000 Cobra R has a weight bias of 56.5/43.5 front to rear. Of course, the Ferrari 550 Maranello has a perfect weight bias, but you'll have to pay $226,620 for it.
There are two ways to handle upgrading your Mustang's suspension. The first is the inexpensive and easy way-install lowering springs and performance shocks and struts. These additions will improve handling characteristics on any car. But if you're serious about your Mustang's handling, you'll need a lot more than shocks and springs to keep up with the competition. Here's where the second, expensive part comes in, but it's also the correct way to prepare your Mustang for all-out open-track duty.
A lot goes into increasing the handling of a car. Not to sound like our 10th-grade science teacher, but physics is not just a class you slept through; it has a huge impact on the handling of any car. Let's face it, if the teacher had applied physics to racing, we would've paid more attention. Physics is "the science of matter and energy and of interactions between the two." In layman's terms, the laws of physics tell us an object in motion will remain in motion until another force is introduced.
Let's apply this to road racing. When your Mustang (matter) has a full head of steam going down the straight, it's an object in motion (energy). When you hit the binders and prepare for a turn, this is the other force being introduced. Since the car was going straight originally, it wants to keep going in that direction. But you want the car to turn. If it doesn't turn the way you want it to, this is called understeer, or a pushing condition. Most front-engined cars suffer from understeer mainly because the weight of the engine is directly over the front wheels. There are several factors causing understeer; one of the major causes is flex. If the chassis is allowed to flex uncontrollably, all that energy is being transferred onto the outside tire going into a turn. To get a handle on your Mustang, controlling its flex is one of the first things you need to do.