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Underframe
Support for the suspension, axles and wheels at chassis level or below it.

Undergeared
Vehicle in which the final drive ratio gives a top speed below the true potential, because
the engine runs out of revs.

Underinflation
Condition in which the tyre pressure is below the recommended figure.

Undershield
Panel fixed to the car's underside to protect components from stone damage or stop water
splashing onto them.

Undersquare engine
One with the bore diameter less than the stroke length.

Understeer
Cornering characteristic in which the tyres at the front develop more slip angle than those at the rear, causing the car's front to run wide on a corner.

Unidirectional Tyre
One designed to rotate in one direction only.

Unitary Construction
Vehicle without a separate chassis frame.

Unitised Body Construction
Complete body structure in which many panels are joined for structural strength and form the chassis frame, body floor, sides and turret.

Universal Joint
Coupling that allows one shaft to rotate at an angle to another without vibration.

Unleaded Petrol
Fuel containing no lead-based additives.

Unsprung Mass
The mass of those components - such as wheels, tyres, brakes and some steering parts - not carried by the main springing system.

Upper Cylinder Lubricant
Special oil mixed with the gasoline to provide lubrication for the valve guides and cylinder walls.

Upshift
The action of changing gear to a more direct gear ratio.

Utility
Load-carrying vehicle, with an enclosed passenger cab and a separate cargo tray.

U-turn
Manoeuvre to reverse direction in one continuous movement.

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This article was written by Bruce Gow, an Australian search engine marketer who does search engine optimization for websites such as Used Car Prices. He has completed extensive research on used cars in both Australia and the USA, but is NOT a used car dealer.

You can reach him at bruce@searchengine-guy.com.au for all used car or SEO (Search Engine Optimisation) enquires in Australia or the USA.