From Nissan 350Z & 370Z Wiki
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Intro
The suspension system has two basic functions, to keep the car's wheels in firm contact with the road and to provide a comfortable ride for the passengers. A lot of the system's work is done by the springs. Under normal conditions, the springs support the body of the car evenly by compressing and rebounding with every up-and-down movement. This up-and-down movement, however, causes bouncing and swaying after each bump and is very uncomfortable to the passenger. These undesirable effects are reduced by the shock absorbers.
"Suspension," when discussing cars, refers to the use of front and rear springs to suspend a vehicle's "sprung" weight. The springs used on today's cars and trucks are constructed in a variety of types, shapes, sizes, rates, and capacities. Types include leaf springs, coil springs, air springs, and torsion bars. These are used in sets of four for each vehicle, or they may be paired off in various combinations and are attached by several different mounting techniques. The suspension system also includes shocks and/or struts, and sway bars.
Most Muscle Cars with automatic transmissions will leave the line hard with good traction (depending on tire adhesion) and no wheel hop. Manual transmission cars are more susceptible to wheel hop due to the harsher and erratic application of power to the rear axle. Faulty alignment of the rear axle, badly worn shocks and/or springs, and loose or faulty bushings in the rear control arms will contribute to the tendency to wheel hop, regardless of the transmission type. Changing the suspension design/operation by using air shocks or coil over shocks will almost always cause wheel hop, because both inhibit the normal rotation of the rear axle assembly. If you have a wheel hop problem and your rear suspension is in normal condition, you may want to try a set of the special lower control arms such as the Indian Adventures "Ground Grabbers." They might help traction as well as preventing or improving wheel hop conditions. The rear of these arms mount lower than stock on the rear axle assembly, thus changing the angle at which they push forward and up on the chassis. The net result is that as the rear axle assembly tries to twist (wind up) in the opposite direction from the forward turning axles, it transfers the twisting torque up and into the chassis. By pushing up against the chassis, the rear axle is forced down and onto the tires harder, and that normally improves traction. This action also inhibits wheel hop.
Removing the front sway bar may not improve traction, and may even degrade it by allowing the car to twist to one side on acceleration. The sway bar is not fastened tightly to the chassis, and thus does not impede front end lift. It merely ties the left and right suspension together so when one wheel either lifts or drops quickly the bar transfers some of the developed energy to the opposite side thus minimizing rolling or wallowing of the vehicle.
The rear sway bar also helps keep the vehicle level from side-to-side which generally helps traction. Concerning the approximately 15# weight, it is located at the optimum spot and that 15# weight may actually help reduce wheel spin.
Exploded Views
Front Suspension Layout
Rear Suspension Layout
General
Where should I start modifying the suspension?
- What is understeer and oversteer? Understeer and oversteer are situations in car handling where, during cornering, the direction of movement of the vehicle does not correspond to the direction in which the wheels are pointing.
- Oversteer occurs when the vehicle turns much more than was desired by the driver. It is a condition more commonly found when cornering forcefully in RWD than FWD vehicles because sudden power to the rear wheels can cause them to slide sideways.
- Understeer occurs when a vehicle turns much less than the driver desired it to. This is more commonly encountered when cornering aggressively in FWD than RWD vehicles because sudden power to the front wheels can cause them to lose traction and push onwards without turning well.
What is the difference between sprung and unsprung weight and why does it matter?
- Simply put, sprung weight is everything from the springs up and unsprung weight is everything from the springs down. Wheels, shocks, springs, joints and tires all contribute to the unsprung weight, whereas the vehicle's chassis, engine and remaining mass all contribute to the sprung weight.
- A key to increasing peformance is by reducing your vehicle's unsprung weight. It not only lightens the car, it also improves the ride and performance of the suspension by taking some of the weight burden off the shocks and springs, allowing them to react faster and less aggressively to irregularities in the road surface.
How Will I Know When I Need Shocks & Struts?:
- Shocks or struts are bad for any one of three reasons. They are bad and need to be replaced when they are leaking oil or broken, or there are symptoms that are directly attributable to the deterioration of the shock or strut. Otherwise, replace them when your ride quality or tire wear indicates service is needed. Again, look for parts with a lifetime warranty. Changing the shocks or struts on a car is normally only done once every 50,000 miles. This is an area of repair where you will see a lot of good deals available.
- However, this is also an area of repair that is very profitable, so watch out. This is a repair that's easy to sell and once the old shocks are thrown away, there is no way to determine if the car really needed them or not. It is also the easiest area for you to bid this type of repair over the phone and where you can bid apples to apples.
Suspension Components
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This pages attempts to explain commonly used suspension terms.
Shock Absorbers
- In the past, a wide variety of direct and indirect shock absorbing devices were used to control spring action of passenger cars. Today, direct, double-acting hydraulic shock absorbers and shock absorber struts have almost universal application.
- The operating principle of direct-acting hydraulic shock absorbers is in forcing fluid through restricting openings in the valves. This restricted flow serves to slow down and control rapid movement in the car springs as they react to road irregularities. Usually, fluid flow through the pistons is controlled by spring-loaded valves. Hydraulic shock absorber automatically adapt to the severity of the shock. If the axle moves slowly, resistance to the flow of fluid will be light. If the axle movement is rapid or violent, the resistance is stronger, since more time is required to force fluid through the openings. By these actions and reactions, the shock absorbers permit a soft ride over small bumps and provide firm control over spring action for cushioning large bumps. The double-acting units must be effective in both directions because spring rebound can be almost as violent as the original action that compressed the shock absorber.
Coil Springs
- Compression type coil springs may be mounted between the lower control arm and spring housing or seat in the frame. Other front suspension systems have the coil springs mounted above the upper control arms, compressed between a pivoting spring seat bolted to the control arm and a spring tower formed in the front end sheet metal. When coil springs are used in both front and rear suspension, three or four control arms are placed between the rear axle housing and the frame to carry driving and brake torque. The lower control arms pivot in the frame members and sometimes support the rear coil springs to provide for up-and-down movement of the axle and wheel assembly.
Leaf Springs
- Front leaf springs are used with solid axle beams in most truck applications. Corvettes use single-leaf, filament-wound, glass/epoxy front and rear springs mounted transversely; i.e., they are crosswise to the vehicle's centerline. Rear leaf springs are used on trucks and some passenger cars. Single leaf or multi-leaf springs are usually mounted longitudinally over the front axle beam or under the rear axle housing. The spring center bolt fastens the leaves together, and its head locates the spring in the front axle beam or saddle on the rear axle housing. U-bolts clamp the spring firmly in place and keep it from shifting. Eyebolts, brackets, and shackles attach it to the frame at each end. Leaf springs also serve as control arms, locating the rear end in position and transferring force to the chassis.
Torsion Bars
- Torsion bar suspension uses the flexibility of a steel bar or tube, twisting lengthwise to provide spring action. Instead of the flexing action of a leaf spring, or the compressing-and-extending action of a coil spring, the torsion bar twists to exert resistance against up-and-down movement. Two rods of spring steel are used in this type of suspension. One end of the bar is fixed solidly to a part of the frame behind the wheel; the other is attached to the lower control arm. As the arm rises and falls with wheel movement, the bar twists and absorbs more of the road shocks before they can reach the body of the car. The bar untwists when the pressure is released, just like a spring rebounding after being compressed.
- Adjusting the torsion bars controls the height of the front end of the vehicle. The adjusting bolts are located at the torsion bar anchors in the front crossmember. The inner ends of the lower control arms are bolted to the crossmember and pivot through a bushing.
Shock Absorber Struts
- A strut is a structural piece designed to resist pressure in the direction of its length. On typical "MacPherson Strut" use, the shock absorber is built into the strut. Most shock absorber struts are hydraulic units. Some MacPherson systems used on Ford vehicles are equipped with low-pressure, gas-filled shock struts. They are nonadjustable and nonrefillable. Like the hydraulic shock struts, faulty units must be replaced as an assembly. Another similar front suspension system is called the "hydraulic shock strut." This strut serves as a shock absorber and replaces the upper control arm. The coil spring, however, is located between the lower control arm and the body structure instead of being mounted directly on the strut.
Sprung and Unsprung Weight
- "Sprung" weight is a term used to describe the parts of an automobile that are supported by the front and rear springs. They suspend the vehicle's frame, body, engine, and the power train above the wheels. These are quite heavy assemblies.
- The "unsprung" weight includes wheels and tires, brake assemblies, the rear axle assembly, and other structural members not supported by the springs.
Sway Bar
- Some cars require stabilizers to steady the chassis against front end roll and sway on turns. Stabilizers are designed to control this centrifugal tendency that forces a rising action on the side toward the inside of the turn. When the car turns and begins to lean over, the sway bar uses the upward force on the outer wheel to lift on the inner wheel, thus keeping the car more level.
Control Arms
- A control arm is a bar with a pivot at each end, used to attach suspension members to the chassis.
- When coil springs are used in both front and rear suspension, three or four control arms are placed between the rear axle housing and the frame to carry driving and brake torque. The lower control arms pivot on the frame members and sometimes support the rear coil springs to provide for up-and-down movement of the axle and wheel assembly.
- A-arms are control arms with two inboard pivots, giving strength. Some front end designs use control arms instead of A-arms, usually to save weight and add adjustability.
Camber Angle
- Camber angle is the angle made by the wheel of your Scion vehicle. More specifically, it is the angle of verticle tilt of the wheels and tires when viewed from the front or rear of the vehicle. Camber must be taken into consideration in the design of steering and suspension components. If the top of the wheel is further out than the bottom (that is, tilted inwards), it is called positive (+) camber; if the bottom of the wheel is further out than the top, it is called negative (-) camber.
- Camber angle alters the handling qualities of the suspension. Negative (-) camber improves grip during cornering maneuvers. The negative angle provides the outer tire which is taking the greatest proportion of the cornering loads, at a better angle to the road, increasing the contact patch of the tire and transmitting the forces perpendicular to the tire, rather than through a shear force across it. On the other hand, for maximum straight-line acceleration, obviously the greatest traction will be attained when the camber angle is zero (neutral) and the tread is flat on the road. Proper management of camber angle is a major factor in suspension design, and must incorporate not only great geometric models, but also real-life behavior analysis of the components such as flex, distortion, elasticity, etc. What was once an art has now become much more scientific with the use of computers, which can juggle all the variables mathematically instead of relying on the designer's intuitive feel and experience, and as a result the handling of even low-priced automobiles has improved significantly.
- In older cars with double wishbone suspensions, camber angle was usually adjustable, but in newer models with McPherson strut suspensions it is normally fixed. While this may reduce maintenance requirements, if the car is lowered by use of shortened springs, this changes the caster angle (as described in McPherson strut) and can lead to increased tire wear and even impaired handling. For this reason, individuals who are serious about modifying their car for better handling will not only lower the body, but also modify the mounting point of the top of the struts to the body to allow some fore/aft movement for caster adjustment. Aftermarket plates with slots for strut mounts instead of just holes are available for most of the commonly modified models of cars.
- Another reason for negative camber is that a rubber tire tends to roll on itself while cornering. If the tire had zero camber, the inside edge of the contact patch would begin to lift off of the ground, thereby reducing the contact patch. By applying negative camber, this effect is reduced, thereby maximizing the contact patch.
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Service Specifications
Front Suspension
This page covers the front suspension service and alignment characteristics of the 350Z. Toe, camber, ride height are covered in the below chart.
Rear Suspension
This page covers the rear suspension service and alignment characteristics of the 350Z. Toe, camber, ride height are covered in the below chart.
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