Slippery/bumpy surfaces

[alex25]

This is apparently different than drag, although I'm not sure how, as they seem closely related. Anyway, I'll add these parameters to Road Atlanta since this seems as good a time as any.

think of drag as proportional to the viscosity of the medium you are moving through. walking in water is always harder than walking in air because water has much higher viscosity. the rolling resistance is a property of the wheel coupled to the properties of the ground through the rolling resistance coefficient. imagine driving in sand. the rolling resistance coefficient drops, so the wheel slips and drag increases as the tire sinks into the sand. the two are not really related.

now, i play a physicist in real life but i haven't done this kind of physics in some 20 years (and i can't be bothered to look it up) so take everything i said with a grain of sand.

anyway, i'll take a look at the code to see what you've implemented.

--alex--