Momentum is the key. Just yesterday I saw an SUV carrying a bicycle on the roof rack slowly enter a garage with low clearance. Although he was just inching along, the bike crumpled like a gum wrapper. Ouch. The same bike on its own would have bounced off the wall undamaged. Downhill momentum favors the heavier rider, but rolling resistance increases with weight. Gravitational acceleration, of course, is the same for all cyclists.