The pump is built as a cartridge/module that slides into a matching wheel hub and locks onto it.  The cartridge includes the wheel axle and one bearing and adds about 4 ounces to the wheel weight. Air is pumped from the end of the hub through a small polyurethane air line that connects to the tire valve stem.  The outer diameter of the hub (center) is about 1.3",  which is similar in size to current bicycle hubs,  and the outer surface of the hub (center) is smooth and cylindrical.

Desired tire pressure is set by the user via an adjustment screw. A small silver lever on the side turns the pump on.  Typically, riding the bike  inflates the tire until it is fully pumped up,  at which point the pump shuts off.  If the tire is flat, the wheel is spun by hand (or for the rear wheel by turning the crank) until there is enough pressure to ride.  This usually takes about a minute.  For a standard road bicycle tire (700 x 23), a good approximation is 1 1/2 miles of riding to pump a tire up from flat.  There is a light drag while spinning with the pump on, which goes away when it shuts off.

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