To attach the down tube or seat tube to the bottom bracket so that the center of these tubes is offset from the center of the bottom bracket, use the Aero tubing option.

In the Tubing tab, select Aero or offset for the down tube. The term Chord length might seem to apply more to an aero tube. However, in the case of a standard round down tube being mounted offset from the center of the BB, the chord length is simply the tube diameter. The term Leading edge offset from centreline just refers to the distance from the front edge of the down tube to what would theoretically be the centerline of a round tube mounted straight through the centerline of the bottom bracket.

The first bicycle was seen in Paris in 1791 and was a form of hobby-horse. The first treadle-propelled cycle was designed by Scotsman Kirkpatrick Macmillan in 1839.