I regularly ride my Steamroller geared at 46/18 to the top. There's really no need to flip your wheel, it's not a long or steep climb. 69 inches is plenty low enough to take you to the top. The observatory itself is still closed due to renovations but the road to the top remains open. Avoid weekends due to tourist traffic near the top. Have fun....keep your bike simple and leave your chaintool, extra chainring and cog at home...