A convertible bicycle, comprising: a front wheel unit, a rear wheel unit, a body frame, a plurality of pedals, a seat, a vertical handle rod, and handlebars, the front wheel unit being connected to the rear wheel unit via the body frame, the plurality of pedals and the seat being disposed on the body frame, the vertical handle rod being disposed on the front wheel unit and the vertical handle rod having a top end and a bottom end; and a vertical frame tube, the vertical frame tube being cylindrical and having a top end, a bottom end, an outer wall, and an inner canal, the vertical frame tube being attached to the body frame by the outer wall, the vertical handle rod passing through the inner canal of the vertical frame tube; wherein the front wheel unit comprises a front wheel and a frontal female interlocking gear, the rear wheel unit comprises a rear wheel, a rear wheel axle, a gear train, and a rear female interlocking gear, the front wheel unit may be removed and the vertical handle rod may interface with the rear female interlocking gear of another convertible bicycle to form a tandem tricycle, and the handlebars are connected to the top end of the vertical handle rod and the frontal female interlocking gear is connected to the bottom end of the vertical handle rod; characterized by the vertical handle rod having an upper rod hole, a lower rod hole, and a canal hole; and an upper connector ring with a screw hole and a lower connector ring with a screw hole, the upper connector ring being disposed on the top end of the vertical frame tube and the lower connector ring being disposed on the bottom end of the vertical frame tube. a front wheel unit, a rear wheel unit, a body frame, a plurality of pedals, a seat, a vertical handle rod, and handlebars, the front wheel unit being connected to the rear wheel unit via the body frame, the plurality of pedals and the seat being disposed on the body frame, the vertical handle rod being disposed on the front wheel unit and the vertical handle rod having a top end and a bottom end; and a vertical frame tube, the vertical frame tube being cylindrical and having a top end, a bottom end, an outer wall, and an inner canal, the vertical frame tube being attached to the body frame by the outer wall, the vertical handle rod passing through the inner canal of the vertical frame tube; wherein the front wheel unit comprises a front wheel and a frontal female interlocking gear, the rear wheel unit comprises a rear wheel, a rear wheel axle, a gear train, and a rear female interlocking gear, the front wheel unit may be removed and the vertical handle rod may interface with the rear female interlocking gear of another convertible bicycle to form a tandem tricycle, and the handlebars are connected to the top end of the vertical handle rod and the frontal female interlocking gear is connected to the bottom end of the vertical handle rod; characterized by the vertical handle rod having an upper rod hole, a lower rod hole, and a canal hole; and an upper connector ring with a screw hole and a lower connector ring with a screw hole, the upper connector ring being disposed on the top end of the vertical frame tube and the lower connector ring being disposed on the bottom end of the vertical frame tube. the front wheel unit comprises a front wheel and a frontal female interlocking gear, the rear wheel unit comprises a rear wheel, a rear wheel axle, a gear train, and a rear female interlocking gear, the front wheel unit may be removed and the vertical handle rod may interface with the rear female interlocking gear of another convertible bicycle to form a tandem tricycle, and the handlebars are connected to the top end of the vertical handle rod and the frontal female interlocking gear is connected to the bottom end of the vertical handle rod; characterized by the vertical handle rod having an upper rod hole, a lower rod hole, and a canal hole; and an upper connector ring with a screw hole and a lower connector ring with a screw hole, the upper connector ring being disposed on the top end of the vertical frame tube and the lower connector ring being disposed on the bottom end of the vertical frame tube.