[MazingerS14]

"helper" springs have almost negligible spring rate and only purpose is to keep the main spring properly seated (and thus prevent rattles and such).  "tender" springs on the other hand can add a "progressive" characteristic to your main spring because of the higher spring rate compared to a "helper" and will help to prevent wheel lift in cars with that problem since it has enough tension to actually push down on the suspension.

Puck