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| Word | Description |
| Scrub Radius | The scrub radius is the distance in front view between the Steering Axis and the center of the contact patch where both would theoretically touch the road. The steering axis is the line between the top pivot point of the hub and the lower ball joint of the hub. On a MacPherson strut, the top pivot point is the strut bearing, and the bottom point is the lower ball joint. The inclination of the steering axis is measured as the angle between the steering axis and the center line of the wheel. This means that if your camber is adjustable within the pivot points you can change the the scrub radius, this alters the width and offset of tires you can safely run on your car. If the steer axis intersection point is outboard of the center of the contact patch it is negative, if inside the contact patch it is positive. |
| Shock (Absorber) | The shock absorber's duty is to absorb or dissipate energy. In general terms, shock absorbers help cushion vehicles on uneven roads. |
| Spherical Bearing | A spherical bearing is a bearing that permits angular rotation about a central point in two orthogonal directions (usually within a specified angular limit based on the bearing geometry). Typically these bearings support a rotating shaft in the [bore] of the inner ring that must move not only rotationally, but also at an angle. |
| Spindle | In an automobile, the spindle is a part of the suspension system that carries the hub for the wheel and attaches to the control arms. |
| Spring Rate | Spring rate is a ratio used to measure how resistant a spring is to being compressed or expanded during the spring's deflection. The magnitude of the spring force increases as deflection increases according to Hooke's Law. Briefly, this can be stated as F = -kx \, where F is the force the spring exerts k is the spring rate of the spring. x is the displacement from equilibrium length i.e. the length at which the spring is neither compressed or stretched. Spring rate is confined to a narrow interval by the weight of the vehicle,load the vehicle will carry, and to a lesser extent by suspension geometry and performance desires. Spring rates typically have units of N/mm (or lb/in). An example of a linear spring rate is 500 lb/in. For every inch the spring is compressed, it exerts 500 lb. A non-linear spring rate is one for which the relation between the spring's compression and the force exerted cannot be fitted adequately to a linear model. For example, the first inch exerts 500 lb force, the second inch exerts an additional 550 lb (for a total of 1050 lb), the third inch exerts another 600 lb (for a total of 1650 lb). In contrast a 500 lb/in linear spring compressed to 3 inches will only exert 1500 lb. The spring rate of a coil spring may be calculated by a simple algebraic equation or it may be measured in a spring testing machine. The spring constant k can be calculated as follows: k = \frac{d^4G}{8ND^3} \, where d is the wire diameter, G is the spring's shear modulus (e.g., about 12,000,000 lb/in or 80 GPa for steel), and N is the number of wraps and D is the diameter of the coil. |
| Steering Ratio | Steering ratio refers to the ratio between the turn of the steering wheel (in degrees) or handlebars and the turn of the wheels (in degrees). In motorcycles and bicycles, the steering ratio is always 1:1, while in most passenger cars, it is between 12 and 20:1. Example: If one complete turn of the steering wheel (360 degrees) causes the wheels to turn 24 degrees, then the ratio is 15:1 (360/24=15). |
| Strut | An automotive suspension strut combines the primary function of a shock absorber (as a damper), with the ability to support sideways loads not along its axis of compression. This means that a strut must have a more rugged design, with mounting points near its middle for attachment of such loads. The most common form of strut in an automobile is the MacPherson strut. The MacPherson strut combines a shock absorber and a spring in a single unit, by means of which each wheel is attached to the car body. |
| Suspension | Suspension is the term given to the system of springs, shock absorbers and linkages that connects a vehicle to its wheels. Suspension systems serve a dual purpose — contributing to the car'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 road wheel in contact with the road surface as much as possible, because all the 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. |
| Suspension Types | Suspension systems can be broadly classified into two subgroups — dependent and independent. These terms refer to the ability of opposite wheels to move independently of each other. A dependent suspension normally has a beam (a simple 'cart' axle) or (driven) live axle that holds wheels parallel to each other and perpendicular to the axle. When the camber of one wheel changes, the camber of the opposite wheel changes in the same way (by convention on one side this is a positive change in camber and on the other side this a negative change). De Dion suspensions are also in this category as they rigidly connect the wheels together. An independent suspension allows wheels to rise and fall on their own without affecting the opposite wheel. Suspensions with other devices, such as sway bars that link the wheels in some way are still classed as independent. A third type is a semi-dependent suspension. In this case, the motion of one wheel does affect the position of the other but they are not rigidly attached to each other. A twist-beam rear suspension is such a system. |
| Sway Bar | A sway bar (aka stabilizer bar, anti-sway bar, roll bar, or anti-roll bar) is an automobile suspension device. It connects opposite (left/right) wheels together through short lever arms linked by a torsion spring. A sway bar increases the suspension's roll stiffness—its resistance to roll in turns, independent of its spring rate in the vertical direction. |