# Frame tubes.

#### Frame tubes.

The classic frame is composed of:

• The top tube.
• The down tube.
• The seat tube.
• The bracket (where the crankshaft is in).
• The chainstays.
• The dropouts.
• The seatstays.

The frame should achieve strong rigid connection between bracket, head tube, seat sling and dropouts.
The two triangles in the frame, the frame tubes are mainly of tension and pressure. Only the tubes are also subjected to bending and torsion forces by stairs on the bottom bracket and torsional forces on the steering head.
Due to the forces on the frame, it will have a tendency to deform in three ways:

1. In the vertical direction the frame will bend through . A large stiffness in the vertical direction makes the frame less comfortable. So suspension in this direction is desirable. In this direction the frame is therefore not to be rigid.
2. The bracket will tend to move out of the frame plane.In a non rigid frame the bracket will be much more swerve to the right through the chain force and turning on the left leg. This allows the chain to come to the front derailleur. If by the lateral movement of the bracket energy is also lost and how much energy that is then, is not known. At first glance it seems that with the lateral push of the bracket force is wasted unnecessarily.
For lateral pushing away of the bracket energy is needed..
However, this energy is stored in the frame.What happens next with this energy is not known. It may be that the energy is converted into heat, it could also be that the energy is again delivered and eventually used to drive the bicycle. Especially in racing bikes with lightweight frame bracket stiffness may be small. If the wall thickness of the frame tubes is reduced without changing the shape of the frame, the bracket stiffness of the lightweight frame will be lower. This can be improved by carrying out a heavier frame, a frame with larger tube diameters or by using oval frame tubes at the bottom bracket in the transverse direction .
3. The head tube will rotate relative to the rear dropouts. Because of this driving behavior may be adversely affected. Especially when heavily loaded bicycles and at high speeds a limp frame can in this direction come in an annoying low-frequency vibration. In ordinary city bicycles stiffness plays no role. Due to the construction and use of thick-walled steel tube, the frames of this bicycles are sufficiently rigid. Critical is the stiffness of lightweight race frames (both the torsional stiffness as a bracket stiffness), ladies frames (torsional stiffness) and tendem frames (torsional stiffness). Under normal circumstances, the frame is sufficiently strong and will not break down. Due to extreme loads such as collisions, falls and vandalism it can still break. The frame is the most vulnerable in the head tube, the bracket and dropouts.

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