Bicycle with chain drive, comprising: a frame comprising a bottom bracket as well as a horizontal rear fork; a rear wheel mounted rotatably in the frame, provided with a rear chain wheel, which rear wheel comprises a rear axle mounted to the frame; a crank set mounted rotatably in the bottom bracket of the frame, provided with a front chain wheel; a chain running about the front and rear chain wheel, closed in itself and defining a chain plane, comprising an upper chain part extending between the front and rear chain wheel and a lower chain part extending between the front and rear chain wheel; wherein the horizontal rear fork comprises at least one fork leg adjacent the rear wheel, of which the front end is connected to the bottom bracket and of which the rear end is provided with an axle mounting part to which an end of the rear axle is connected, which fork leg crosses said chain plane in a cross point between the front chain wheel and the rear chain wheel and between the upper chain part and the lower chain part; a chain tensioner engaging the lower chain part, for keeping the lower chain part tensioned; wherein the chain tensioner comprises a carrier mounted rotatably to the frame, as well as two guide wheels (110, 120) mounted rotatably to the carrier, wherein the rotation axes of the carrier and of the guide wheels (110, 120) are mutually substantially parallel and are substantially perpendicular to the said chain plane; wherein the lower chain part, coming from the front chain wheel, engages the lower side of a front one of said chain wheels, then runs over the upper side of the rear one of said guide wheels, and then engages the lower side of the rear chain wheel; and characterised in that the carrier is provided with bias means exerting a bias force on the carrier for moving the rear one of said guide wheels up; and wherein the chain tensioner is mounted in the space between the rear chain wheel and the said cross point; wherein the plane defined by the rotation axis of the carrier and the rotation axis of the front guide wheel and the plane defined by the rotation axis of the carrier and the rotation axis of the rear guide wheel make an angle with each other in the range of 80° - 100° and preferably an angle of about 90°; wherein the mutual distance between the rotation axis of the carrier and the rotation axis of the front guide wheel is such that, in the lowest rotation position of the front guide wheel, the lowest point of the chain is located higher than or at the most at equal level with the initial lower chain contour. a frame comprising a bottom bracket as well as a horizontal rear fork; a rear wheel mounted rotatably in the frame, provided with a rear chain wheel, which rear wheel comprises a rear axle mounted to the frame; a crank set mounted rotatably in the bottom bracket of the frame, provided with a front chain wheel; a chain running about the front and rear chain wheel, closed in itself and defining a chain plane, comprising an upper chain part extending between the front and rear chain wheel and a lower chain part extending between the front and rear chain wheel; wherein the horizontal rear fork comprises at least one fork leg adjacent the rear wheel, of which the front end is connected to the bottom bracket and of which the rear end is provided with an axle mounting part to which an end of the rear axle is connected, which fork leg crosses said chain plane in a cross point between the front chain wheel and the rear chain wheel and between the upper chain part and the lower chain part; a chain tensioner engaging the lower chain part, for keeping the lower chain part tensioned; wherein the chain tensioner comprises a carrier mounted rotatably to the frame, as well as two guide wheels (110, 120) mounted rotatably to the carrier, wherein the rotation axes of the carrier and of the guide wheels (110, 120) are mutually substantially parallel and are substantially perpendicular to the said chain plane; wherein the lower chain part, coming from the front chain wheel, engages the lower side of a front one of said chain wheels, then runs over the upper side of the rear one of said guide wheels, and then engages the lower side of the rear chain wheel; and characterised in that the carrier is provided with bias means exerting a bias force on the carrier for moving the rear one of said guide wheels up; and wherein the chain tensioner is mounted in the space between the rear chain wheel and the said cross point; wherein the plane defined by the rotation axis of the carrier and the rotation axis of the front guide wheel and the plane defined by the rotation axis of the carrier and the rotation axis of the rear guide wheel make an angle with each other in the range of 80° - 100° and preferably an angle of about 90°; wherein the mutual distance between the rotation axis of the carrier and the rotation axis of the front guide wheel is such that, in the lowest rotation position of the front guide wheel, the lowest point of the chain is located higher than or at the most at equal level with the initial lower chain contour.