EIBACH SUSPENSION GLOSSARY
- Anti-dive is a suspension characteristic that affects the amount of suspension travel when the brakes are applied. When a car is decelerating due to braking there is a load transfer off the rear wheels and onto the front wheels. Vehicle properties such as the center of gravity height, total weight, deceleration rate and wheelbase affect the amount of dive a vehicle experiences. 100% anti-dive refers to no change in front suspension height under braking. This is achieved by adjusting the pivot points of the suspension system or through hydraulics in the front dampers.
- Rear suspension kinematic characteristic which reduces the amount of pitch under braking forces. Street cars may have up to 150% anti-lift for driver comfort.
Anti-Roll Bar (aka: stabilizer bar, sway bar - from anti-sway bar)
- A transverse torsion bar linking both sides of a suspension system with bushings mounted on the chassis that allow it to rotate freely. The bar’s ends are connected to or shaped as lever arms, with attachments to the suspension linkages at each side via ball-joint links, rubber-bushed pivot links, or as on race cars, spherical rod ends called Heim joints. When both wheels take a bump equally, the wheels move the same amount without twisting the anti-roll bar. Individual wheel movement or body roll will force the bar to twist as the lever arms are moved, thereby adding the bar’s own spring rate to that of the car’s springs. Although an anti-roll bar’s main function is to reduce body roll in cornering, it also influences overall handling. You can fine-tune Over- or Understeering Tendencies.
- When a car is accelerating forward, there is a load transfer off the front wheels and onto the rear wheels. Vehicle properties such as the center of gravity height, total weight, acceleration rate and wheelbase affect the amount of squat a vehicle experiences. 100% anti-squat refers to no change in rear suspension height under acceleration. This is achieved by adjusting the pivot points of the suspension system or through hydraulics in the rear dampers.
- The geometric center and innermost point of a turn or corner on a roadway or race course.
- Description of handling characteristics of a vehicle, describing understeer, neutral, or oversteer.
- Weight added to a vehicle usually to bring it to a minimum weight requirement-useful for adjusting balance in racing vehicles.
- Torsional stiffness of the antiroll bar (or torsion bar), either at the drop links or at the wheel's contact patch. This is usually expressed in N/mm or lb/in.
- Linkage component with a central pivot and multiple link attachment points. Usually used with inboard suspensions to transfer loads from the pull/push rod to the spring/damper. Technically, a "rocker" uses the same pivot for pullrod and damper, while a bell crank has different attachments for each.
- Vertical movement of wheel towards chassis. Aka deflection, jounce. In racing, the terms "bump and droop" are used together to define suspension travel. For OEM" jounce and rebound".
- Change in toe angle under bump/droop. Normally, slight toe-in with bump is used in the rear and slight toe-out with bump is used in the front to aid stability. Excessive bump steer in the front can be caused from incorrect angle of the steering tie-rods from excessive lowering.
- The wheel angle relative to ground/chassis in front/rear view. Negative camber is when the tops of the wheels are closer together than the bottoms. Tuning the amount of negative camber can be very useful in achieving maximum grip in racing. Excessive negative camber can wear the inside edge of the tires under acceleration or braking and reduces grip. Not enough negative camber can wear the outside edge of the tire while cornering and reduces grip.
- The caster angle identifies the forward or backward slope of a line drawn through the upper and lower steering pivot points when viewed directly from the side of the vehicle. Caster is positive if the line angles towards the rear of the vehicle at the top, negative if the line angles towards the front. Positive caster improves directional stability.
Center of Gravity (CoG)
- The exact point around which an object, such as a vehicle, is perfectly balanced in every direction. It’s the center point of the vehicles mass. The position of the center of gravity affects stability and handling: lower is usually more stable.
- The apparent force that draws a rotating body away from the center of rotation. Centrifugal force is not a true force; it is a form of inertia.
- Named after Colin Chapman of Lotus Racing. It is basically a MacPherson type strut used in a rear suspension.
- A term used to describe a type of spring.
- When a spring is compressed to a point that the coils make contact. The spring has travelled to its maximum compressed height or at full block.
- Coilover is short for “coil spring over shock”. Consists of a shock absorber with a coil spring assembled together as one unit. Some coilovers (Eibach: Pro-Street-S) have adjustable ride height using an adjustable spring perch.
- It’s actually a torsion bar, wound into a helical shape. It’s the Heart of the Suspension System carrying the car’s weight under all static and dynamic conditions, absorbing the shocks from uneven roads and bumps, and correctly positioning all other suspension components. But it can provide only partial roll resistance as the Anti-Roll Bars (Eibach: Anti-Roll-Kit) provide additional support.
- The displacement of sprung and unsprung masses in the suspension system in which the distance between the masses decreases from that at static condition. Compression damping is the primary factor in ride quality, road compliance and steering response.
Control Arm (aka: A-arm)
- A hinged suspension link between the chassis and strut or wheel hub. A Double A-Arm suspension has upper and lower control arms. A control arm may also attach to a spring, damper, anti-roll bar and pull/push rod.
- The ability of a vehicle to travel through a curved track or highway. Cornering force (side force) is the lateral force that will push the vehicle toward the outside of the corner while cornering.
- Optimizing the weight of the vehicle at each wheel to maximize the vehicles transitional response. Tire traction and suspension movements are determined by the force (weight) on each corner of the vehicle. Equal diagonal weighting provides the best transitional response while equal front weight provides the best braking response. Adjustable ride height coilovers (Eibach Pro-Street-S) allow easy fine tuning for maximum and balanced cornering performance without adding ballast.
Damper (aka: shock absorber)
- Shock/strut used to dampen the kinetic energy of a spring and control rate of load transfer. All hydraulic dampers (shock absorbers) work by the principle of converting movement into thermal energy (heat). For that purpose, fluid in the damper is forced to flow through restricted holes and valve systems, thus generating hydraulic resistance. See also shock absorber.
- Digressive damping describes a style of damper valving. Digressive means that as damper shaft speed increases, damping forces increase at a decreasing rate. In comparison, a linear rate damper follows the same increasing path. This allows for sport dampers (Eibach Pro-Damper) to offer more low speed control for performance handling without being overly harsh on rough roads or big bumps.
Dive (aka nose-dive)
- Vehicle pitch under braking.
- Independent suspension design with a short upper and long lower arm connecting chassis to suspension upright. Each arm is in the form of an A or V when viewed from above. Very common in racing; allows precise control of camber and roll center.
- (aka: double a-arm)
Downforce (aka negative lift)
- Downwards thrust created by the cars aerodynamics, typically through wings and spoilers. Additional downforce allows a car to corner faster by increasing the vertical force on the tires, which creates more grip.
Droop (aka rebound)
- Amount of down travel of a suspension system. In racing, the terms 'bump and droop" are used together to define suspension travel; automotive engineers call it "jounce and rebound".
- Attach anti-roll bar to suspension arms, upright or strut. The name comes from the typical configuration: a link drops down from the anti-roll bar to the lower suspension arm.
Dynamic Weight Distribution
- Weight distribution while driving under transient handling or aerodynamic forces.
Full Coil Suspension
- A vehicle suspension system in which all four wheels have their own coil spring.
Gas-filled Shock Absorber (aka: gas shock or damper)
- A shock that uses nitrogen gas, to pressurize the fluid in the shock to reduce or prevent aeration or foaming which can cause cavitation and loss of damping.
- The amount of adhesion (traction)a tire has to the road.
Heavy-Duty Shock Absorber
- Shock absorbers having reinforced seals, a mono-tube design to reduce heat build-up, and a rising rate valve for precise spring control.
- A very soft spring used in racing to prevent the Main Spring (or Main- and Tender Spring) from becoming loose in the spring seats, when the suspension is unloaded or at full droop.
- 1) Suspension spring system where the spring/damper is mounted near or within the chassis via rocker and pull/push rod system. Principal advantage is removing the spring/damper from the airstream, improving drag and downforce on ground effects cars (motorsport).
- 2) Brake system where the disk and caliper are mounted on the sprung mass, via axles and CV joints. Principal advantage is reducing unsprung mass. (motorsport)
- Any suspension which is not a solid axle type. This allows each wheel to move vertically (reacting to bumps or road irregularities) independently form each other.
- The wheel and tire motion is constrained by the suspension links on the vehicle, the motion of the wheel package in the front view will scribe an imaginary arc with an "instantaneous center" of rotation at any given point along its path. The instant center for any wheel package can be found by following imaginary lines drawn through the suspension links to their intersection point.
- Vertical force applied on chassis under cornering. This force can lift the vehicle if the roll center is above ground or drop if underground. Susceptible with swing axle suspension design. Typically, jacking will cause a slight increase in ride height and slight loss of camber while cornering, which results in loss of grip.
- Temporary lowering of chassis on bumpy roads due to excessive rebound damping.
Jounce (aka bump)
- The upward travel or compression of the spring and shock absorber.
- Describes the motion characteristics of a suspension, as opposed to the force characteristics (motion ratios).
- The energy an object possesses due to motion.
- Opposite of downforce.
To raise a vehicles ride height for additional ground clearance to increase off-road capability. Eibach offers two types of fully engineered lifting:
- Pro-Lift-Kit: For light off-road use, this suspension spring system lifts the vehicle on average up to 30mm. Engineered to maintain top-performance handling and excellent ride quality, the added ground clearance will allow for exploring your favorite dirt roads with confidence.
- All-Terrain-Lift: For the serious off-roader, these are complete spring and damper systems that will lift your vehicle up to 3.5” depending on application. Designed to tackle whatever the road conditions, the additional clearance also allows for a larger wheel and tire package to further your off-road capability. Precision engineered to deliver maximum performance, as well as improved response and control over rugged terrain—all while maintaining class leading street comfort and handling.
Linear-rate coil spring
- A coil spring with equal spacing between the coils, one basic shape, and constant wire diameter having a constant deflection rate regardless of load.
- Aka oversteer (motorsport—NASCAR).
Lowering (aka suspension lowering)
Lowering the vehicles CoG. The main goal in lowering a vehicles CoG with the suspension is to improve handling and stability (street performance and motorsport). As always there is a right way and a wrong way to lower a vehicle.
Yes—Right way: With a properly engineered lowering suspension kit (Eibach Pro-Kit, Sportline and Pro-Street-S), the components fit perfectly into the factory locations and maintain proper fitment from full droop to full jounce. The lower CoG benefits are many, both in performance and appearance:
- Performance: reduced nose dive under braking, squat while accelerating and body roll when cornering. Also, with the reduced ride height there is another benefit that is often overlooked: better aerodynamics. Since less air goes underneath the vehicle (where most aerodynamic drag occurs) it requires less horsepower to move the vehicle forward. The results, better fuel efficiency and higher top speeds (motorsport).
- Appearance: The lower CoG and corresponding ride height reduces excessive fender-well clearance giving the vehicle a more aggressive stance: Traction + Attraction!
No—Wrong way: Improper lowering (short springs, cut springs, heating springs) can be very dangerous; too low results in improper suspension arm angles causing severe bump steer, improper wheel alignment and the suspension and/or chassis bottoming out—which can all contribute to a complete loss of handling and control. Short or shortened springs can fall out of their spring seats at full droop, which can cause a severe accident. Heating the spring causes the spring to lose tensile strength and will cause the spring to fail and collapse very quickly. Lowering the wrong way can lead to catastrophic results and a much bigger expense in repairs to get it corrected.
- Type of car suspension system which uses the top of a telescopic damper as the upper steering pivot. It is widely used in the front suspension of modern vehicles and is named for Earle S. MacPherson, who developed the design.
- Inboard suspension system which is actuated by both left and right wheels to a single spring/damper. All roll resistance is then carried by the antiroll bar. (motorsport - Formula series).
- The difference of motion on a vehicles suspension spring and shock travel for a given amount of wheel travel. If the spring is half the distance from the control arm pivot as the wheel, the motion ratio relative to the wheel is 1 to 2.
- Common on independent suspension systems, using three or more lateral arms instead of only one upper and lower control arm per corner.
- Handling characteristic between understeer and oversteer. This is usually the goal of chassis tuning, with a slight bias towards over or under-steer depending on track conditions and driver preference (motorsport).
- Lateral distance between a wheel's vertical centerline and hub face. Positive offset has wheel center line further outboard than hub face; generally found on front wheel drive vehicles and newer rear wheel drive vehicles. Improper offset can negatively affect the handling of a vehicle.
- Traditional suspension system where the spring/damper is mounted directly between the chassis and lower/upper arm or upright.
- The lengths of a vehicle, either front and rear, which extend beyond the wheelbase.
- Vehicle handling characteristic that occurs when a car turns (steers) by more than (over) the amount commanded by the driver. Therefore, the rear wheels tend to lose traction before the front.
- Amount of longitudinal (accel. & braking) slip between the tire and the road. This is expressed as the ratio of the velocity of slipping to the CL wheel velocity. As with slip angle, there is an optimum percent slip for maximum grip, beyond which the tire spins. (Motorsports).
- Viewed from the side, the change in vehicle angle with respect to the ground. For example, in braking, weight is transferred from the rear to the front, causing unloading of rear springs and additional load on the front springs, resulting in nose dive. The effect may be reduced or eliminated with anti-pitch suspension geometry, lower CoG, longer wheelbase or higher spring rates.
Polar Moment of Inertia
- The resistance of an object to rotational acceleration. When the mass of an object is distributed far from its axis of rotation, the object is said to have a high polar moment of inertia. When the mass distribution is close to the axis of rotation, it has a low polar moment of inertia. A mid-engine car has most of its mass within its wheelbase, contributing to a low polar moment of inertia, which, in turn, improves cornering turn-in.
Pre-Setting (aka Blocking)
- A complex production technology. All Eibach suspension springs go through the Pre-Setting process. Designed to expand the stress levels to higher limits each spring is compressed to full block, meaning all coils make contact under pressure. This allows new engineering limits to design superior products and to make springs permanently block-resistant—no more sagging! All product design characteristics will now be maintained for the life of the spring, unless damaged; physically or by corrosion.
- A spring system (Eibach Pro-Kit = Progressive Spring Kit) that increases in spring rate with increase in deflection/travel.
- Inboard suspension component which place the spring/damper unit inboard and out of the air stream to further reduce air resistance. The pull rod typically attaches near the upper ball joint and pulls on the inboard rocker when in bump. Pull-rod designs often have somewhat lower and more non-linear motion ratios due to packaging of the rocker next to the ground, which allowed the designers to put more components close to the car's floor, lowering its center of gravity. (Motorsport)
- Aka understeer (motorsport—NASCAR).
- Inboard suspension component which place the spring/damper unit inboard and out of the air stream to further reduce air resistance. The push rod typically attaches near the lower ball joint and pushes on the inboard rocker when in bump. Push-rods may be preferred to pull-rods for more adjustability with higher and more linear motion ratios, however may introduce buckling concerns. (Motorsport)
- The wheel and suspension go back down away from the chassis. The main function of rebound in a damper (shock absorber) is to control the speed by which the suspension travels during rebound—controlling the spring rate on the car. Rebound damping also provides the roll control of the vehicle.
- A suspension system where the spring rate increases when the wheels move further into jounce. This action can be accomplished by configuring the geometric shape of the suspension, by using progressive rate springs (Eibach Pro-Kit) which change tension as they are compressed, or by using two or more springs with rubber stops. The purpose of a rising-rate suspension is to maintain consistent ride and handling characteristics under a variety of situations: loaded or unloaded, straight roads or curves, and smooth roads or bumpy.
- The ability of a vehicle to maintain contact with the road surface under all conditions. The constant contact of the tires to the ground is crucial for the vehicle to steer, brake and accelerate.
- The vehicle’s ability to absorb shocks from irregular road surfaces and keep them from the passenger compartment.
- Inboard suspension component used to transfer wheel loads to the spring. The rocker may be either an entire suspension control arm (usually the upper arm) or a component between the pull/push rod and spring.
- A line that connects the front and rear roll centers. If the axis runs nose-down, the car tends to oversteer. If the axis runs nose-up, the car tends to understeer.
- The theoretical point around which the chassis rolls, and is determined by the design of the suspension. Front and rear suspensions have different roll centers. The amount that a chassis rolls in a corner depends on the position of the roll axis relative to the car’s center-of-gravity (CoG). The closer the roll axis is to the center of gravity, the less the chassis will roll in a corner.
Roll Couple Distribution (RCD)
- The ratio of weight transfer of the front and rear wheels, usually expressed as a percentage. The roll couple percentage is a simplified method of describing lateral load transfer distribution front to rear, and subsequently handling balance. It is the effective wheel rate, in roll, of each axle of the vehicle as a ratio of the vehicle's total roll rate. It is commonly adjusted through the use of anti-roll bars (Eibach Anti-Roll-Kit), but can also be changed through the use of different spring rates.
- Expressed as degrees of chassis roll per G of lateral acceleration. Street cars range between 2.5° and 6°. Most race cars 0.3° - 0.8° (ground effects cars essentially do not roll -- below 0.1° is common). Excessive roll stiffness degrades handling on bumpy circuits. Insufficient roll stiffness reduces transient response and tire grip.
- The roll moment is the product of the sprung mass and the square of the distance between the vehicle's roll center and its center of mass. If the vehicle is subjected to centrifugal forces, such as in a turn, the roll moment will cause the body to rotate (lean) towards the outside of the turn. Together with the roll stiffness, this factor determines the roll flexibility.
- Roll rate is similar to a vehicle's ride rate, but for actions that include lateral accelerations, causing a vehicle's sprung mass to roll about its roll axis. It is expressed as torque per degree of roll of the vehicle sprung mass. It is influenced by factors including but not limited to vehicle sprung mass, track width, CG height, spring and damper rates, roll center heights of front and rear, anti-roll bar stiffness and tire pressure/construction. The roll rate of a vehicle can, and usually does differ front to rear, which allows for the tuning ability of a vehicle for transient and steady state handling. The roll rate of a vehicle does not change the total amount of weight transfer on the vehicle, but shifts the speed at which and percentage of weight transferred on a particular axle to another axle through the vehicle chassis. Generally, the higher the roll rate on an axle of a vehicle, the faster and higher percentage the weight transfer on that axle.
- The resistance to chassis roll from the springs, anti-roll bars or both. Together with the roll moment, the total roll stiffness of the vehicle affects the roll flexibility.
- Lateral displacement of the wheel centerline in bump/droop due to an instant center above or below ground. Suspension design should keep scrub to a minimum to reduce unwanted side loads generated during a bump. Scrub is not the same as "scrub radius".
- The distance in front view between the steering axis and the center of the contact patch of the wheel, where both would theoretically touch the road. If these lines intersect at the road surface, a zero scrub radius would be present. When the intersection is below the surface of the road, this is positive scrub radius. Conversely, when the lines intersect above the road, negative scrub radius is present. The point where the steering axis line contacts the road is the fulcrum pivot point on which the tire is turned. Scrub radius is changed whenever there is a change in wheel offset as on the tyre line where the wheels are pushed outboard causing scrub radius to become more (+). Older cars tended to have very close to zero scrub radius but often on the (+) side, newer cars with ABS all have negative scrub radius (that's why all the newer cars have the wheels offset more inboard).
- The sidewall distance from the wheel rim to the unloaded tread surface. A low section height improves transient response; a high section height improves ride quality.
- Maximum width of an unloaded tire. Wider is normally better for grip, though excess width may result in insufficient tire temperatures and unnecessary unsprung weight.
- Any independent suspension system with short upper arms and long lower arms (double a-arm, multi-link).
Single Wheel Bump Rate
- Vertical wheel travel spring rate when only one wheel hits a bump. When this occurs the anti-roll bar does alter the spring rate. What happens is that the anti-roll bar twists as the wheel is raised—since the other wheel does not move. The bar twists over its whole length adding this spring rate to the suspension spring rate.
- A circular area of flat pavement used for various tests of a car's handling. The most common skidpad use is testing lateral acceleration, measured in g-force.
- Referring to tires—the indirect measure of the fraction of the contact patch that is sticking.
- The angle between a rolling wheel's actual direction of travel and the direction towards which it is pointing. Tire grip increases with slip angle until a certain point, at which the tire starts to skid.
- Suspension where left and right wheels are rigidly connected. They are nearly universally used in heavy-duty trucks and most light and medium duty pickup trucks, SUVs, and vans. Still used in motorsport: circle track, Trans Am and off-road.
- A mechanical device, which is typically used to store energy due to resilience and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces. They are made of an elastic material formed into the shape of which returns to its natural length when unloaded. Springs come in various forms: helical coil, torsion beam, leaf (semi-elliptical), rubber (polyurethane) bushing and air bag. The helical coil spring (Eibach Pro-Kit and Eibach Racing Springs—ERS) are most commonly used in street performance vehicles and motorsport. The other spring types are nearly universally used in heavy-duty trucks and most light and medium duty pickup trucks, SUVs, and vans.
- The spring rate (or suspension rate) is a component in setting the vehicle's ride height or its location in the suspension stroke. When a spring is compressed or stretched, the force it exerts is proportional to its change in length. The spring rate or spring constant of a spring is the change in the force it exerts, divided by the change in deflection of the spring. Vehicles which carry heavy loads will often have heavier springs to compensate for the additional weight that would otherwise collapse a vehicle to the bottom of its travel (stroke). Heavier springs are also used in performance applications where the loading conditions experienced are more extreme.
- Springs that are too hard or too soft cause the suspension to become ineffective because they fail to properly isolate the vehicle from the road. Vehicles that commonly experience suspension loads heavier than normal have heavy or hard springs with a spring rate close to the upper limit for that vehicle's weight. This allows the vehicle to perform properly under a heavy load when control is limited by the inertia of the load. Riding in an empty truck used for carrying loads can be uncomfortable for passengers because of its high spring rate relative to the weight of the vehicle. A race car would also be described as having heavy springs and would also be uncomfortably bumpy. However, even though we say they both have heavy springs, the actual spring rates for a 2,000 lb (910 kg) race car and a 10,000 lb (4,500 kg) truck are very different. A luxury car, taxi, or passenger bus would be described as having soft springs. Vehicles with worn out or damaged springs ride lower to the ground which reduces the overall amount of compression available to the suspension and increases the amount of body lean. Performance vehicles require different spring characteristic than average vehicles.
Spring Sag (aka: sagging)
- The loss of spring load and length caused by a poor design, insufficient material or excessive loading beyond its physical limits. Over time, this can cause the spring to collapse or even break. There is a stress limit even for the best materials, but the max allowed stress levels are then superior. But even those high stress levels can be expanded by special production technologies - see Pre-Setting (aka: Blocking). All Eibach Performance and Motorsport Springs are preset to avoid any sagging.
- In a vehicle with a suspension, sprung mass (or sprung weight) is the portion of the vehicle's total mass that is supported above the suspension, including in most applications approximately half of the weight of the suspension itself. The sprung weight typically includes the body, frame, the internal components, passengers, and cargo.
- Vehicle pitch under acceleration.
- see anti-roll bar.
Static Weight Distribution
- Static weight distribution is the weight resting on each tire contact patch with the car at rest, exactly the way it will be driven or raced (with driver – motorsport).
- Lever arm rigidly attached to upright or hub, which is connected to the tie rod. Steering arm and tie rod placement define the Ackerman steering system.
- Static friction, usually referring to suspension, is friction that needs to be overcome to enable the motion of stationary objects. Higher stiction in a suspension, may lead to unpredictable chassis heights and poor handling.
- The term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels and allows relative motion between the two. Suspension systems serve a dual purpose — contributing to the vehicle's road holding/handling and braking for good active safety and driving pleasure, and keeping vehicle occupants comfortable and reasonably well isolated from road noise, bumps, and vibrations, etc. These goals are generally at odds, so the tuning of suspensions involves finding the right compromise. It is important for the suspension to keep the wheel in contact with the road surface as much as possible, because all the road or ground forces acting on the vehicle do so through the contact patches of the tires. The suspension also protects the vehicle itself and any cargo or luggage from damage and wear. The design of front and rear suspension of a car may be different.
- See anti-roll bar.
- Simple independent suspension of 1 lateral link rigidly connected to the wheel (early VW Beetle). With this design, wheel camber changes radically through the suspension stroke.
- Linear or progressive Tender Springs combined with Main springs provide a dual or multi-stage Suspension characteristic with a softer initial rate and a firmer final rate. (Motorsport – Eibach ERS)
- A mix of materials that goes into making a tire. For performance and motorsport it’s mainly about the hardness of rubber - softer is stickier, harder lasts longer.
- The symmetric angle that each wheel makes with the longitudinal axis of the vehicle. Positive toe, or toe in, is the front of the wheel pointing in towards the centerline of the vehicle. Negative toe, or toe out, is the front of the wheel pointing away from the centerline of the vehicle. Toe can be measured in linear units, at the front of the tire, or as an angular deflection. Front wheels that toe-out slightly is preferred for turning response and toe-in for rear wheels adds stability.
- In chassis design to prevent flex. Geometric configuration of chassis tube members. By adding a diagonal member, connected corners are held at a fixed distance. They can't be spread apart or moved closer together. Despite pivots for corners, the structure cannot be forced out of shape, and is therefore rigid. The additional member to a four-sided structure forms two triangles in the structure. This is called triangulation.
- Suspension and chassis adjustments to optimize handling.
Understeer (aka: push)
- Vehicle handling characteristic when a car steers less than (under) the amount commanded by the driver, meaning the front wheels tend to lose traction before the rear.
- The mass of the suspension, outboard brakes, wheels and other components directly connected to them, rather than supported by the suspension. The unsprung weight of a wheel controls a trade-off between a wheel's bump-following ability and its vibration isolation. Bumps and surface imperfections in the road cause tire compression—which induces a force on the unsprung weight. The unsprung weight then responds to this force with movement of its own. The amount of movement, for short bumps, is inversely proportional to the weight - a lighter wheel which readily moves in response to road bumps will have more grip and more constant grip when tracking over an imperfect road. In contrast, a heavier wheel which moves less will not absorb as much vibration; the irregularities of the road surface will transfer to the cabin through the geometry of the suspension and hence ride quality and road noise are deteriorated. For longer bumps that the wheels follow, greater unsprung mass causes more energy to be absorbed by the wheels and makes the ride worse.
- See static weight distribution.
- Square root of (wheel rate/sprung mass carried by wheel). A characteristic of suspension stiffness that may be used to compare cars of different weights. Race cars typically have higher front frequencies than rear to reduce dive and improve traction; street cars are the opposite for "flat ride" over bumps.
- Wheel rate is the effective spring rate when measured at the wheel. This is as opposed to simply measuring the spring rate alone. Wheel rate is usually equal to or considerably less than the spring rate since springs are mounted on control arms, swing arms or some other pivoting suspension member. Wheel rates are usually summed and compared with the sprung mass of a vehicle to create a "ride rate" and corresponding suspension natural frequency in ride (also referred to as "heave"). This can be useful in creating a metric for suspension stiffness and travel requirements for a vehicle.
- The distance between the centers of the front and rear wheels. Longer wheelbase improves stability, shorter wheelbase improves maneuverability.
- The angle between vehicle centerline and actual direction of motion around a turn. (oversteer/understeer).