I always thought grind in Gravel grinder refereed to hard or unpleasant work or preserving through a difficult task not the pedaling style to be employed.
Gravel Grubbing?
Gravel Travel?
Gravel Humping? ( not that kind of humping you pervs)
Gravel Devil?
Gravel Pickle?
Gravel Jackpot? (not the fun kind of jackpot)
Probably none of these are what OP had in mind.