Bicycle frame with passive seat tube pivot joint
A bicycle frame assembly that includes an upper frame member and a lower frame member that each extend between a head tube and a dropout. A seat tube extends between the upper frame member and the lower frame member. The seat tube is preferably connected to a bottom bracket of the lower frame member and is connected by a pivot to the upper frame member so that the seat tube can deflect from a rest position without altering an orientation of a top tube to a bottom tube of the upper and lower frame members, respectively.
1. A bicycle frame assembly comprising:
a forward frame triangle comprising:
a top tube having a first end connected to a head tube and a second end;
a bottom tube having a first end connected to the head tube and a second end;
a bottom bracket connected to the second end of the bottom tube; and
a flexible, unitary seat tube extending in an upward direction from the bottom bracket;
a pair of seat stays connected to the top tube and extending in a rearward direction beyond the forward frame triangle; and
a coupling connecting the seat tube to the forward frame triangle proximate the top tube at a location nearer a bicycle seat than the bottom bracket.
2. The bicycle frame assembly of claim 1 , further comprising a passage formed proximate an intersection of the seat stays and the top tube and shaped to accommodate the seat tube passing therethrough.
3. The bicycle frame assembly of claim 2 , wherein an axis of the coupling is oriented normal to an axis of the passage.
4. The bicycle frame assembly of claim 1 , wherein the flexible, unitary seat tube is made of a fiber reinforced plastic.
5. The bicycle frame assembly of claim 1 , wherein the seat tube can rotate at least 7 degrees about the coupling allowing the seat tube to deflect from an at rest shape.
6. The bicycle frame assembly of claim 1 , wherein a longitudinal axis of the coupling is one of positioned forward of a longitudinal axis of the seat tube, aligned with the longitudinal axis of the seat tube, or positioned rearward the longitudinal axis of the seat tube.
7. A bicycle frame assembly comprising:
an upper frame member that includes a top tube and a pair of seat stays and that extends between a dropout and a head tube;
an opening formed in the upper frame member;
a lower frame member that includes a bottom tube, a bottom bracket, and a chain stay, and that extends between the dropout and the head tube;
a flexible, unitary seat tube extending from the lower frame member toward the upper frame member and passing through the opening in the upper frame member; and
a coupling connecting the seat tube to the upper frame member proximate the opening so that more of the seat tube is located between the coupling and the bottom bracket than extends beyond the upper frame member.
8. The bicycle frame assembly of claim 7 , wherein the coupling is oriented either forward or rearward relative to a longitudinal center-line of seat tube.
9. The bicycle frame assembly of claim 7 , further comprising a bridge that extends between the pair of seat stays and defines a rear wall of the opening.
10. The bicycle frame assembly of claim 7 , wherein the flexible, unitary seat tube is made of a fiber reinforced plastic.
11. The bicycle frame assembly of claim 7 , wherein the coupling includes a first portion and a second portion located on opposite sides of the flexible, unitary seat tube.