Post by Luis on Oct 31, 2005 22:33:00 GMT -5
There are literally hundreds of details that affect the handling of any car. Even narrowing it down to the most important still leaves us with a long list:
Wheel rate (spring rate at the wheels)
Shock damping
Suspension geometry
Caster
Camber
Toe
Motion ratio
Roll center
Instant center
Anti squat
Anti dive
Bump steer
Suspension deflection
Chassis rigidity
Center of gravity
Polar moment of inertia
Tire size, compound and pressure
Unsprung weight
Track width
With so many important details, where do you start? The first thing to do is to sort out the things you can easily control and deal with them first. Right from the start this means using a quality tire and setting your alignment properly. (For more on setting your alignment, see Steeda Alignment Basics). Next, you want to address chassis and suspension deflection, suspension geometry, spring rates and shock tuning. Finally, other things like polar moment of inertia and track width, while important, take a lot more work to change enough to make an appreciable difference. These can be left alone until the other major areas have been addressed.
Eliminating Deflection in the Chassis and Suspension
The first area to consider for improving the handling of the Mustang is deflection. Deflection is another way of saying that something moves when a load is applied to it. There are two kinds of deflection we are concerned with. The first is deflection of the bushings in the suspension. As cornering forces are applied to the suspension, the bushings that connect the control arms to the body and axle are forced out of their normal shape. A small amount of this compliance is necessary to allow the control arms to move through their normal range of motion without binding, and to maintain acceptable levels of ride quality and noise isolation. Unfortunately, during hard corners the stock bushings deflect far too much for ideal handling.
In the rear, hard corners stretch the bushings so far out of shape that the axle will actually move laterally by more than an inch. Not only does the axle move sideways, it will “steer” at an angle as well*. This excessive movement makes the handling unpredictable as the axle shifts around. The solution is to control the movement of the axle by reducing the deflection of the control arm bushings. This is easily done, by installing better upper and lower control arms with firmer bushings. A word of caution though: the angle of the upper rear control arms requires the bushings to twist as they go through their normal range of motion. Simply installing the hardest bushings you can find will cause the suspension to bind, creating a whole new set of problems. At Steeda we carefully select the bushing size, shape and material to prevent bind.
Better control arms are the simplest way control the lateral deflection of the axle, and are a good choice for the majority of Mustang drivers. The ultimate lateral control of the rear axle can be obtained by installing a panhard rod. However, to properly use a panhard rod, the angled factory upper control arms must be eliminated to prevent the roll center defined by the panhard rod from conflicting with the roll center defined by the upper arms. (More on this in a later article.) This, in turn, requires a new way to control the rotation of the axle. Steeda’s 5-Link suspension is a complete system for the rear suspension, incorporating a panhard rod and parallel upper control arms to control the motion of the axle.
In the front, the control arm bushings deflect from the load of cornering, allowing the arm to move sideways relative to the car. The tie-rods, on the other hand, don’t deflect very much. Since the steering angle of the front wheels is controlled by the tie-rod’s relationship to the front spindle, and the spindle is mounted to the front control arm, the deflection of the front control arm bushings causes the steering angle to change as the load on the control arm changes during a corner. The deflecting bushings also allow the camber angle of the front wheel to change. As the bushings on the heavily loaded side of the car deflect inward from the force of cornering, the tire tilts outward at the top, reducing the amount of negative camber. Again, this unwanted deflection reduces both cornering grip and steering predictability. This deflection can be cured, by installing polyurethane A-arm bushings. Caster angle can be improved at the same time by using Offset A-arm bushings, which push the control arm slightly forward.
The other kind of deflection we are concerned with is Chassis Deflection. As loads from the suspension are transmitted to the body of the car, the body itself twists and bends in response to those forces. This twisting, or deflection, has many undesirable consequences. The suspension was designed to move in a very precise range of motion to control the wheels. When the car itself deflects, the suspension attachment points move. This changes all of the carefully designed geometry of the suspension system. It’s like having your car constantly redesigning itself as you drive down the road. Nothing good will come of this. In addition, after it is deflected the twisting chassis will spring back to its original position. Unlike the suspension, there is no shock absorber to dampen this springing motion. Not only is this bad for handling, but ride quality also suffers from the unwanted twisting and shaking of the body.
To reduce chassis deflection, several braces have been developed to strengthen the Mustang chassis. Subframe Connectors, sometimes called frame-rail connectors, reinforce the connection between the front and rear suspension systems. A strut tower brace is used to strengthen the upper strut mounts, which helps control the alignment as the front suspension is loaded from bumps and cornering forces. The Steeda G-trac™ brace connects between the rear bushings of the lower control arms, to strengthen the front suspension crossmember. Finally, a rollbar can be added to strengthen the midsection of the car. Using these parts to stiffen the chassis can improve both ride quality and handling at the same time.
Now that we have the basics of suspension and chassis deflection covered, we can move on to the real keys to making the Mustang handle. In the next installment of our suspension seminar we will talk about spring rates, shocks, and suspension geometry.
* This “rear steering” is not to be confused with “roll-steer” which is another phenomenon entirely that we will cover in a later installment.
Wheel rate (spring rate at the wheels)
Shock damping
Suspension geometry
Caster
Camber
Toe
Motion ratio
Roll center
Instant center
Anti squat
Anti dive
Bump steer
Suspension deflection
Chassis rigidity
Center of gravity
Polar moment of inertia
Tire size, compound and pressure
Unsprung weight
Track width
With so many important details, where do you start? The first thing to do is to sort out the things you can easily control and deal with them first. Right from the start this means using a quality tire and setting your alignment properly. (For more on setting your alignment, see Steeda Alignment Basics). Next, you want to address chassis and suspension deflection, suspension geometry, spring rates and shock tuning. Finally, other things like polar moment of inertia and track width, while important, take a lot more work to change enough to make an appreciable difference. These can be left alone until the other major areas have been addressed.
Eliminating Deflection in the Chassis and Suspension
The first area to consider for improving the handling of the Mustang is deflection. Deflection is another way of saying that something moves when a load is applied to it. There are two kinds of deflection we are concerned with. The first is deflection of the bushings in the suspension. As cornering forces are applied to the suspension, the bushings that connect the control arms to the body and axle are forced out of their normal shape. A small amount of this compliance is necessary to allow the control arms to move through their normal range of motion without binding, and to maintain acceptable levels of ride quality and noise isolation. Unfortunately, during hard corners the stock bushings deflect far too much for ideal handling.
In the rear, hard corners stretch the bushings so far out of shape that the axle will actually move laterally by more than an inch. Not only does the axle move sideways, it will “steer” at an angle as well*. This excessive movement makes the handling unpredictable as the axle shifts around. The solution is to control the movement of the axle by reducing the deflection of the control arm bushings. This is easily done, by installing better upper and lower control arms with firmer bushings. A word of caution though: the angle of the upper rear control arms requires the bushings to twist as they go through their normal range of motion. Simply installing the hardest bushings you can find will cause the suspension to bind, creating a whole new set of problems. At Steeda we carefully select the bushing size, shape and material to prevent bind.
Better control arms are the simplest way control the lateral deflection of the axle, and are a good choice for the majority of Mustang drivers. The ultimate lateral control of the rear axle can be obtained by installing a panhard rod. However, to properly use a panhard rod, the angled factory upper control arms must be eliminated to prevent the roll center defined by the panhard rod from conflicting with the roll center defined by the upper arms. (More on this in a later article.) This, in turn, requires a new way to control the rotation of the axle. Steeda’s 5-Link suspension is a complete system for the rear suspension, incorporating a panhard rod and parallel upper control arms to control the motion of the axle.
In the front, the control arm bushings deflect from the load of cornering, allowing the arm to move sideways relative to the car. The tie-rods, on the other hand, don’t deflect very much. Since the steering angle of the front wheels is controlled by the tie-rod’s relationship to the front spindle, and the spindle is mounted to the front control arm, the deflection of the front control arm bushings causes the steering angle to change as the load on the control arm changes during a corner. The deflecting bushings also allow the camber angle of the front wheel to change. As the bushings on the heavily loaded side of the car deflect inward from the force of cornering, the tire tilts outward at the top, reducing the amount of negative camber. Again, this unwanted deflection reduces both cornering grip and steering predictability. This deflection can be cured, by installing polyurethane A-arm bushings. Caster angle can be improved at the same time by using Offset A-arm bushings, which push the control arm slightly forward.
The other kind of deflection we are concerned with is Chassis Deflection. As loads from the suspension are transmitted to the body of the car, the body itself twists and bends in response to those forces. This twisting, or deflection, has many undesirable consequences. The suspension was designed to move in a very precise range of motion to control the wheels. When the car itself deflects, the suspension attachment points move. This changes all of the carefully designed geometry of the suspension system. It’s like having your car constantly redesigning itself as you drive down the road. Nothing good will come of this. In addition, after it is deflected the twisting chassis will spring back to its original position. Unlike the suspension, there is no shock absorber to dampen this springing motion. Not only is this bad for handling, but ride quality also suffers from the unwanted twisting and shaking of the body.
To reduce chassis deflection, several braces have been developed to strengthen the Mustang chassis. Subframe Connectors, sometimes called frame-rail connectors, reinforce the connection between the front and rear suspension systems. A strut tower brace is used to strengthen the upper strut mounts, which helps control the alignment as the front suspension is loaded from bumps and cornering forces. The Steeda G-trac™ brace connects between the rear bushings of the lower control arms, to strengthen the front suspension crossmember. Finally, a rollbar can be added to strengthen the midsection of the car. Using these parts to stiffen the chassis can improve both ride quality and handling at the same time.
Now that we have the basics of suspension and chassis deflection covered, we can move on to the real keys to making the Mustang handle. In the next installment of our suspension seminar we will talk about spring rates, shocks, and suspension geometry.
* This “rear steering” is not to be confused with “roll-steer” which is another phenomenon entirely that we will cover in a later installment.
