My HPV Street Machine is Rohloff equipped. Has anybody got any idea what is supposed to be the optimal number of teeth on the front cog (is that the chain ring?) and on the rear one? I think I've got 50-odd on the front on mine. Secondly to what extent do those Schlumpf gadgets extend the gear range (I'm thinking of hilly areas i.e. extending at the low rather than the high end)?