Different shorts for Tri bike vs road bike?

Just to clarify - you can wear road bike shorts on any bike you want, same with tri shorts! You don't have to be riding a tri bike to wear tri shorts and vice versa. The different between tri shorts and regular cycling shorts is that you can't really swim or run in regular cycling shorts because the chamois is too thick. Tri shorts have less padding. But you can wear either kind of shorts to ride either kind of bike. There's no law In a triathlon, you'd probably want to stick to tri shorts for the reasons I specified above. But it has nothing to do with the kind of bike you're riding.