S2Thizzle

It depends which track and organization your choose. With every group I've run with, no aftermarket roll bar was required. When you choose an event to attend, just make sure to contact someone from that group and ask.

Thunderhill has it's own HPDE which requires either a hardtop or roll bar. However, I strongly believe a hardtop is not suitable for rollover protection and should not be relied upon for such purposes. You can't go wrong with a well-built bolt-in roll bar.