Truck Equipment Glossary - S

SAE
Abbreviation for Society of Automotive Engineers.  
 
Safety Chains
Chain assemblies used to connect the towing and towed vehicles as a secondary coupling system. 
 
School Bus
A bus that is sold or introduced in interstate commerce for purposes that include carrying students to and from school or related events. Does not include a bus designed and sold for operation as a common carrier in urban transportation.
 
School Bus Passenger Seat
A seat in a school bus other than the driver’s seat.
 
Self Regeneration System
An onboard system that converts a hybrid vehicle’s kinetic energy (energy of motion) into potential energy (stored electricity or high-pressure hydraulic fluid) during deceleration or braking (regenerative braking). This energy is then returned to the drive system during subsequent operations.
 
Semitrailer 
A trailing unit that is supported in the rear by its own suspension system and at the front by the towing vehicle. This type of unit is sometimes supported by a separate suspension unit with towing provisions (thus becoming a full trailer). An exception is the utility-type trailer, house trailer, etc. that is towed by a ball coupling (referred to simply as a trailer and is not designed as semi- or full trailer).
 
Serial Number
A number stamped on a metal plate by the manufacturer and placed on a component or the vehicle for identification purposes. See Vehicle Identification Number (VIN).
 
Set-back Front Axle
The front steering axle is normally as close to the front of the vehicle as the design and wheel and tire size permit. When the front axle is purposely located farther toward the rear, it is referred to as being “set back.” Center line of front axle to front of front bumper is normally from 28" to 37" on regular models and 48" or more on set-back front-axle models. The purpose of moving the axle rearward is to increase loads applied to the front axle and increase maneuverability. Standard type front-axle setting generally enables more economical cab construction and meets axle spread requirements of states using the Bridge Formula.
 
Shipping Weight
The dry weight of a complete truck with all standard equipment including grease and oil but without any fuel or coolant. 
 
Short Chain

Method of attaching a tow sling to a towed vehicle so that the tow chains support the entire load.
 
Side Rails
Upper or lower extensions of the body sides that run longitudinally, front to back.
 
Single & Double Reduction Gears
Generally rear-axle terminology. Standard rear-axle gearing is single reduction, (i.e., one step of speed reduction through the rear-axle gearing). In certain heavy-duty applications a double reduction is desirable. This permits a greater gear reduction in a smaller gear case, thus allowing better road clearance and more compact design.
 
Slideback Cylinder
A hydraulic cylinder, usually a long stroke, mounted horizontally at front of body used to slide body forward or rearward.
 
Snatch Block
A single or multiple pulley used to reduce cable load or change cable direction. 
 
Spacer
Steel or wood section between chassis frame and body underframe to give proper tire clearance and/or required ground-to-floor height.
 
Spacer Block
Used in conjunction with 4x4 wood beam to provide additional clearance between the tow bar, chains and body of the vehicle. 
 
Spade
One or more hydraulically operated ground-penetrating feet designed primarily to resist rearward movement.
 
Speedability
The speed a vehicle will attain based on engine power, gross weight, power train efficiency, air resistance, grade resistance and road type.  
 
Splash Guard

See Mud Flap. 
 
Spring Capacity
(1) Capacity at Pad: The total weight that the spring can support in its maximum position; (2) Capacity at Ground: The total weight that the spring can support in its maximum position plus a portion of the weight not supported by the springs.
 
Stabilizers
Hydraulic or manually operated leg devices attached to trucks to give additional support down to the ground for improved stability. Examples are outboard legs, outriggers and jack legs.
 
Stake Pockets
Apertures in the floor or sides of bodies for the reception of stakes.
 
Stakes
Metal or wood posts by means of which sides are attached to platforms; when used alone stakes are a means of retaining loads on flat deck platforms.
 
Steering Wheel Lock
Independent device used to secure the steering wheel of a towed vehicle.  
 
Stationary Lighting Loads
Vehicle electrical loads that provide lighting on stationary vehicles for work area protection or safety (e.g., flashers and strobe lights) and interior and exterior work area lighting.
 
Steering Wheel Lock
Independent device used to secure the steering wheel of a towed vehicle.
 
Stopping Distance
The distance traveled by a vehicle from the point of application of force to the brake control to the point at which the vehicle reaches a full stop. 
 
Stroke
(1) In engines, the distance traveled by a piston from top dead center to bottom dead center; (2) Maximum distance traveled by the piston in an air or hydraulic cylinder.
 
Sub Pan
Horizontal surface installed either between or above crossmembers prior to insulation and installation of flooring in reefers.
 
Suction Line
A tubular connection between a reservoir or tank and the inlet of a hydraulic pump.
 
Supply Tank
An oil reservoir used in the hydraulic system.
 
Sustainability
The use of methods, systems and materials that minimize or avoid resource depletion and harm to natural cycles.
 
Swing Axle
A drive axle arrangement found on some passenger cars and some light-duty trucks. The differential is mounted rigidly on the vehicle frame and the axle shafts are allowed to “swing” as the vehicle moves up and down while running. Lower unsprung weight is one advantage of this system. Universal joints are required on each half of the drive axle to accommodate the vertical motion.
 
Synchronized or Synchromesh Transmission
A truck transmission with built-in devices to automatically match the rotating speeds of the transmission gears. With this type of transmission, “double clutching” is not necessary.