Zenith Aircraft developed a new nose gear shock suspension system for the Zenith CH 650 / CH 750 series kit aircraft that uses stacked rubber shock disks (or "donuts") as an optional replacement to the single nose gear bungee shock cord ring (that has been in use since the 1980s). Using these stacked silicon rubber “donut” disks, the new shock suspension system is expected to last longer and to provide increased shock absorption, while also being adjustable to allow for increased or lowered tension (to better accommodate different engine weights on the nosewheel).
This new nosegear shock suspension system is an optional replacement to the nose gear bungee system. Existing Zenith CH 650 (including the CH601XL-B models) and CH 750 series kits can be updated with the new nosegear shock suspension system.
More info:
http://www.zenith.aero/profiles/blogs/nosegear-shock-suspension