The frame of the bicycle is the part in which all components are directly or indirectly attached to. It is also by far the largest part of the bike and the frame construction is extremely decisive for the character of the bike.
- The frame connects the following four components:
- bottom bracket. (For mounting bottom bracket and crankset).
- saddle post lug. (For mounting seatpost and saddle).
- Head tube. (For mounting fork and handlebar).
- Rear dropouts. (For mounting of the rear wheel).
To the frame can be confirmed all sorts of components such as the rear brake, luggage rack, mudguards, stand, bottle cage, derailleur, lock and cable guides.
- A bicycle frame must have the correct geometry, focusing on expected conditions of use and the height of the rider. The geometry of the frame, is the distance and the angles between the bracket, the saddle post lug, the head tube and dropouts. Frames of racing bikes, mountain bikes, city bikes and touring bikes have a different geometry. Also, frames for people of different length have a different geometry.
- The frame should not break down during use by the forces which the road surface and rider exercised and on the frame. At this point, however, bicycle frames stand out hardly. Each manufacturer is required in order to construct his frames that they are sufficiently safe. They are therefore extensively tested by manufacturers. Better materials and structures are not used to make the frame more strongly, but rather to make frames lighter while retaining the same strength.
- The frame should not be too heavy. High frame weight is particularly disadvantageous when accelerating and climbing bike. Weight is often seen as the most important feature of the frame. The importance of weight reduction of the speed is usually overestimated. Especially in the flat Netherlands has a slightly higher weight hardly affect the speed. However, weight saving is usually expensive.
- The frame should not distort too much by the forces that are put in place when cycling. In particular, the kick forces must be transmitted efficiently. The bracket may also not move too much sideways while cycling. The extent to which the frame from bending is designated by the term rigidity.
- The finish of the frame should be good. This applies to the paint, cams, lugs and weld beads. With more expensive bikes, this is usealy better than with cheaper bikes.
- The frame must have the appropriate cams, depending on the future use. For instance, mountain bake-frames with cams for the mounting of cantilever brakes or V-brake.
- In addition to having the correct geometry, a frame must also be properly focused. Especially for the steering head, the bracket and the rear dropouts, it is important that the position relative to each other is good. It is also important that the bottom bracket and head tube been centered properly so that the bottom bracket and head tube bearing to be mounted in the correct manner. With more expensive bikes manufacturer pays attention to this more than cheaper bikes.