In (almost) every fully test report from BIKE there is a diagram with the suspension characteristics on the test letter. The blue line stands for the suspension fork and the red line for the rear triangle. We determine this characteristic curve on our "Triceratops" test rig from the Zedler Institute for Bicycle Technology and Safety.
The diagram describes the ratio of force (y-axis) to travel (x-axis). The spring characteristic curve can be either progressive, linear or degressive. A linear characteristic curve means that twice the force must be applied for twice the suspension travel. Suspension forks with steel springs, for example, have very linear characteristic curves. With a progressive spring characteristic curve, on the other hand, the resistance increases over the course of the spring travel. So if you want to compress twice as far, you would have to exert three times as much force (depending on the progressiveness). Due to their design, air suspension forks always have a progressive characteristic curve. With a degressive characteristic curve, the resistance decreases over the course of the spring travel. Only a few manufacturers use this type of characteristic curve for MTB rear triangles in order to achieve a plush rear end - without sacrificing efficiency.
The spring characteristic curve can be divided into three parts: The breakaway torque (1), the progression in the spring travel (2) and the end progression (3). Ideally, the breakaway torque is barely perceptible, the middle section of the spring travel increases linearly - so that you don't rush through the spring travel - and the end progression prevents noticeable bottoming out.
Deviations can result in the following losses:
- Excessive breakaway torque results in uncomfortable, wooden response behaviour and the wheel has no traction. Tip: Tuning dust wiper with lower friction.
- If the characteristic curve is too flat in the centre section, the suspension travel is rushed and the suspension generates too little counterpressure. Tip: Increase the compression stage.
- If the end progression kicks in too early, the suspension travel cannot be utilised. If there is too little end progression, the spring elements often bottom out. This is not only unharmonious, but also puts unnecessary strain on man and machine. Tip: Installing or removing volume spacers.
