I clean and lube the bikes about once a week or when the drive train gets noisy
The wife will only ride on mups and the one's around here are gravel for the most part
I spray the drive train done with Gunk Foamy engine degreaser everywhere let sit a while
then use a bristle brush then hose off and relube with Tri-Flo. or chain lube
This size can lasts forever
http://www.lifeandhome.com/gunk-foam...FUxgMgodm1gALQ