Automotive Glossary

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U

U Bolts

U shaped bolts used to fix leaf springs to the axle or other similar tasks such as fixing a steering rack to the body.

U/J

Universal Joint.

Ultra Violet

A frequency of light that is above the visible spectrum.

Ultraviolet

Light/Radiation lying in the ultraviolet range; wave lengths shorter than light but longer than X rays i.e. beyond the violet end of the spectrum/rainbow.

Ultraviolet (UV) Light

That portion of the spectrum which is largely responsible for the degradation of paints. It is invisible to the eye and may also be referred to as "black light." Special UV lamps can be used to cure some paints and adhesives.

ULW

Unladen Weight – The weight of a vehicle inclusive of the body and all parts which are ordinarily used with the vehicle when working on a road. Unladen weight does not include the weight of water or fuel used for the propulsion of the vehicle,
or of loose tools and loose equipment.

Unburned Hydrocarbons

Engine or fuel tank emissions in the exhaust gas, fuel line vents or lubricating oil vapours. Harmful to health. Also HC or THC (total hydrocarbon content of exhaust gas).

Under-bake

The result of curing a paint film at too low a combination of time and temperature. The film may be too soft for good durability.

Undercoat

A first coat; primer, sealer, or surfacer applied to the substrate. Frequently used to provide corrosion protection and adhesion.

Understeer

Steering condition of a turning vehicle when the vehicle attempts to turn by a lesser degree than the steered position taken by the driver. This condition is usually provided by vehicle design in order to improve the driveability of the vehicle.

Underwritten

Sign and accept liability (legal).

Unequal Wishbones

Suspension type with an upper wishbone shorter than the lower wishbone. The geometry of this layout keeps the wheel camber reasonably constant during suspension movements. Also SLA suspension.

Unidirectional

Move in one direction only.

Unidirectional Clutch

A clutch, used in starter motors for example, to only allow drive to pass in one direction.

Union Nut

A hollow nut used to secure hydraulic pipes.

Unit-body Construction

Vehicle body and chassis constructed as a single unit. As distinct from a separate chassis and body construction. Also unitary body construction.

Unitary Body Construction

Vehicle body and chassis constructed as a single unit. As distinct from a separate chassis and body construction. Also unit-body construction.

Universal Joints

Rotating shaft coupling that permits angular axial displacement. Some types will also operate with linear misalignment of axes.

Unladen

Not carrying a load.

Unleaded Petrol

Petrol without any added lead to improve the octane rating.

Unsprung Mass

The part of the vehicle not supported by the suspension springs. The road wheels, hubs, brakes and part of the suspension system.

Unsprung Mass (Weight)

The part of the vehicle not supported by the suspension springs. The road wheels, hubs, brakes and part of the suspension system.

Up Draft

A carburettor where the choke tube (venturi) is fitted vertically and the air enters from the bottom. Upwards movement of air.

Upper Beam

The upper of the two headlamp beams. Also driving beam and main beam.

Upper Control Arm

The upper and shorter wishbone in an independent suspension system.

Upper Quartile

Data is split into 4 equal quarters. The highest quarter is referred to as the Upper Quartile. For example the Upper Quartile of 100 is the highest 25 of the numbers.

Urethane

A type of paint or polymer which results from the reaction of an isocyanate with a hydroxyl containing component. Urethanes are noted for their toughness and abrasion resistance.

USA

United States of America: North American republic containing 50 states - 48 states in North America plus Alaska in northwest North America and the Hawaiian Islands in the Pacific Ocean; achieved independence in 1776.

UV

Ultra violet.

UV Stabilizers

Chemicals added to paint to absorb the ultraviolet radiation present in sunlight. Ultraviolet radiation decomposes the polymer molecules in a paint film and thus UV stabilizers are used to prolong paint life.

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