Transmission ratio between rear swing arm and rear shock

Characteristic curve transmission ratio

Kinematic analysis of the suspension system

The transmission ratio between rear swing arm and rear shock is used to tune the chassis kinematics with the shock element. This consideration is generally travel-based, i.e. change in spring travel on the rear wheel axle to change in the rear shock stroke. The analysis is based purely on position and takes no account of force elements, e.g. that of the rear shock. As a result conclusions are only drawn on the overall kinematic system, while the dynamic factors of influence are not taken into account.

ROTWILD specific tuning of the chassis kinematics with the suspension element

It is important for us that our ROTWILD chassis kinematics should always be optimally tuned to the nonlinear parameters of the latest shock absorber generation. For purposes of optimization, we divide the overall spring travel into three regions:

  • Sag range (20-30% of the total spring travel)
  • Effective spring travel range (30-85% of the entire spring travel)
  • End range (85-100% of the entire spring travel)

Diagram of the suspension travel

Sag range (20-30% of the total suspension travel)

This range is essentially determined by the position of the virtual pivot point and initial section of the wheel trajectory curve.

Effective suspension travel range (30-85% of the entire suspension travel)

This is known as the working range of the rear shock, i.e. the range in which the rider most frequently operates when travelling uphill, riding over obstacles and also during descents. When optimizing the parameters, we aim to achieve a curve for the transmission ratio that is as linear as possible and hence a linearly increasing force on the rear wheel. The chassis then perfectly supports and carries the rider. In addition, the linear curve of the chassis makes it very easy to adjust (air pressure setting on rear shock) to individual body weight.

End range (85-100% of the entire suspension travel)

The end range is necessary to minimize bottoming out on the rear shock and provide reserves of suspension travel. End progression that sets in too early may result in the total suspension travel not being used sufficiently so that the chassis quickly hardens. Contrary to the trend of describing a suspension system exclusively via the term ‘progression’ we regard it as considerably more important to achieve an optimum design for the individual subranges of the suspension travel.

Schematic illustration of forces at the rear wheel

Dynamic analysis of the suspension system

The dynamic analysis of the suspension system concerns the movement of the rear swing arm under the influence of forces. The energy fed into the entire system, e.g. by an impact, is transferred mechanically to the rear swing arm and into the rear shock (conservation of energy).

The aim of our optimization is to minimize the forces acting on the frame components, to guide the energy caused by impacts exclusively into the rear shock and convert it into heat (dissipation). This prevents vibrations due to elastic deformation of the frame components.

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