Uncork

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Free a motorcycle from a sealed or constrained state to unleash its power.

In general use, it can simply mean to open up the throttle to obtain top speed.

More specifically, it means to modify a stock motorcycle by removing factory-installed engine restrictions, which “plug up” the engine’s performance. The restrictions are due to government emission control requirements. Such modifications would also require carburetor adjustments to optimize the performance.

Under Brake

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Failure to apply the brakes to their full capability, resulting in a longer than needed stopping distance. This is usually caused by fear of the results of over braking.

Unit Construction

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Motorcycle or automobile engine design where both the engine and gearbox are integrated within the same casing. Earlier engine design was a pre-unit construction where engine and gearbox were in separate casings.

Unloading

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Reducing the weight, or load, on the motorcycle suspension.  Examples: The front and rear suspension of a motorcycle are completely unloaded when the bike is on a stand with both tires off the ground.  Hard acceleration will load a motorcycle’s rear suspension and unload the front suspension.  A “wheelie,” with the front wheel off the ground, would represent a completely unloaded front suspension.  (Compare Loading).

Unsprung Weight

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The mass of the motorcycle that is not supported by the suspension, such as the wheels, brakes, tires, etc. (Also known as unsprung mass). For comparison, the rest of the motorcycle that is supported by the suspension is called the sprung mass or sprung weight.

Upside-Down Forks

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Telescopic forks that are installed inverted compared to typical forks. In this case the slider tubes are at the bottom and the heavier bodies are at the top. This decreases the unsprung weight of the motorcycle and improves its handling. Also known as inverted telescopic forks.