Anti-vibration springs while in motion. I already lost the other side drum spring which must have flown off at some point with out me hearing or feeling it. I think a slight vibration now exist. I'll have to test in the next week or so.
These are the lightest drums on the market without mentioning the Aluminum GM types that could probably be adapted with a trick that I thought of a long time ago using a GM type bolting/end flange pattern.