Parametric airless tire

This design is inspired by Bridgestone's airless tire concept:

http://www.physorg.com/news/2011-12-bridgestone-airless-concept-tokyo.html

Using the natural springiness of plastic, this design can absorb shock and vibration in a manner similar to a pneumatic tire, but cannot be punctured.

Videos here:
http://www.youtube.com/watch?v=3LctFwZhY1M
http://www.youtube.com/watch?v=sXBgaaI7dHY

This design is fully parametric.

Update: Added tiny (0.001) offset between spirals. Openscad errored when trying to export an STL otherwise.