U

 

 

UNCONTROLLED FINAL POSITION

A final position reached by a traffic unit after an accident without conscious human intervention.

 

UNCOUPLING LEVER OR ROD

A rod with a bent handle forming a lever, usually attached to the end sill, by which the lock of the automatic coupler is opened and the cars uncoupled without going between them.  The lever proper is the part attached to the rod and operating the unlocking mechanism, but in the case of freight cars, the lever and rod are generally made in one piece.

 

UNDAMPED

Un-damped systems are those in which there are no forces opposing the vibratory motion to dissipate energy.

 

UNDER DRIVE

Refers to a condition in which the vehicle's transmission is in a gear having a ratio less than 1:1, that is, the engine crankshaft turns at a faster rate than the vehicle's drive shaft.  Opposite of overdrive.  (Also see direct drive).

 

UNDER STEER

A characteristic of a motor vehicle that results in a tendency to steer toward the outside of a curve.  Motor vehicles with more weight on the front wheels than on the rear or with too little pressure in the front tires are likely to understeer at high speed.

 

UNDERBODY  

Assembly of the floor pan and rear compartment pan assemblies forming the lower closure of the body.

 

UNDERBODY DEBRIS

Debris consisting of mud, dust, rust, paint, snow, or road tar loosened by collision from the underside of the vehicle body, fenders, and other parts.

 

UNDERSTEER

A vehicle is understeer at a given trim if the ratio of the steering wheel angle gradient to the overall steering ratio is greater than the Ackerman steer angle gradient.

 

UNDERSTEER/OVERSTEER GRADIENT

The quantity obtained by subtracting the Ackerman steer angle gradient from the ration of the steering wheel angle gradient to the overall steering ratio.

 

UNIFORM ACCELERATION

Uniform acceleration is a constant acceleration, meaning that the speed changes at a constant rate.

 

UNIFORM VEHICLE CODE

A specimen set of motor vehicle laws, designed and advances as a comprehensive guide or standard for state motor vehicle and traffic laws.

Units
Setup parameter to select the display units of measure in the ProDriver ( Detroit )

UNIVERSAL JOINT

A coupling providing transmission of power through an angle.

 

UNREPORTED ACCIDENT

An accident which is not reported by police, but may be reported to an insurance company, doctor, or to no one.

 

UNSPRUNG MASS

The un-sprung masses are the equivalent masses which reproduce the inertia forces produced by the motions of the corresponding un-sprung parts.

 

UNSPRUNG WEIGHT

The part of the weight of the motorcycle which is not supported on springs (wheels and tires).

 

UPC

Uniform parts code, designed to classify auto parts and used primarily for cost accounting.

 

UPPER BACK PANEL

Portion of body sheet metal between backlight and decklid.

 

UPPER STRUCTURE

The portion of the body including the roof and glass areas.

 

URBAN AREA

An area within boundaries fixed by State or Local officials designated by the US Bureau of Census as having a population of 5,000 or more, and not within another urban area.