How to model gearratio into a power->velocity bicycle model with Simulink

I'm working on power to velocity model for cycling in Simulink. It works fine, until I add gearratios and something goes wrong in de simulation. The problem is there is hardly any difference between a 20/16, 40/16 en 60/16 (front/rear) gearratio, where in reallife the difference would be significant (See plots). And after about 1 second the 20/16 gear ratio makes a weird transition to way higher accelerations and velocity.

It seems something is wrong in the calculation of de force depending on the given power and gearratio. I already tried to overcome this with limiting the maximal rounds per minute (RPM) of the pedal and the maximal possible force produced by the rider, but it doesn't have much of an influence.

vStart and Fstart are now values of velocity and force at t=0 (and become zero at t=0.00000001) to overcome dividing by zero in F=P/v, not pretty but it works for now. (any solutions are welcome though).

• How do I properly model gearratios in my power to velocity model? What connections do I overlook or get wrong in the model?