I had the same inquiry an called or emailed Progressive. The response was something about spring rate. The Harley is a heavier bike so the springs are stiffer. The person said it would be like riding a hardtail.

SOLD: 07 Black BA, 39mm FCRs, TPUSA stage 1 head, TPUSA 813 cams, TPUSA 10.8:1 pistons, TTP #3 igniter, Specialty Spares Long Cannons, Tsukayu Hard Bags. 82HP/55tq NEW: 19 Goldwing Tour DCT