I know everybody recommends using a lockring with the track cog on a converted freewheel hub. But after putting in a spacer for chain alignment there isn't enough room on the threads for a lockring on any hub I have used. I have never had a problem with a cog loosening on me and, in fact, have a heck of a time removing the cog when I go to change it. Does anybody else go without a lockring without problems?