I have carved many dirt bike seats, the carving knife does work nice for your initial cut, then shape the seat with the grinder and flap disk. Softly! Imperfections will show under your cover, so you want the finished product to be smooth, you CANT get it smooth with the knife. Just know once you cut a chunk off, it's gone, so start small, or for your first time just start shaping the seat with the grinder and flap disk. It's much easier to keep,your shape this way