I flew as a passenger on a straight wing Citation II a few years back in order to be positioned to pick up an aircraft. This aircraft would occasionally land on gravel runways. The crew told us that the nosewheel had an auto-spinup feature in order to reduce the likelihood of gravel being picked up and hitting the belly. This is part of the optional gravel kit installation.
A look at the nosewheel showed that there did appear to be some sort of add-on to the axel(perhaps axle) portion of the wheel.
There is mention about it in this link.
1977 | 1244 | Flight Archive