They used a special urethane wheel instead of steel. Not quite as durable, but you experienced the ride difference.
[edit -> fixed typo]
lincoln "Windows XP has so many holes in its security that any reasonable user will conclude it was designed by the same German officer who created the prison compound in "Hogan's Heroes." - Andy Ihnatko, Chicago Sun-Times [link|mailto:bconnors@ev1.net|contact me]
The hills and curves are wide enough that there is no lateral or vertical jarring as well, like on the Beast. That thing beat the shit out of me. And then there's the time that my son convinced me to ride the back seat on the Blue Streak...