Have ridden the Needles highway four times and each time I'm more impressed with the scenery and the natural formation of the surrounding land. If you have the time take it in both directions. Spend some time at the summit, parking can be difficult, limited space.
I have rode it many times. Traffic will be heavy lots of cages that like to stop in the road.
The road is in very good shape. And definitely run it both ways. It is an awesome ride with lots of twisty. Take lots of pictures.
I ride it about once a year. You can ride the Needles and Iron Mountain in the same day or catch some of the side roads also and make a longer trip out of it. If you do the Needles and then Iron Mountain you will come out of the tunnel and will be looking at the Presidents at Rushmore 9Very cool). The tunnels and some parts of the road are only wide enough for 1 vehicle or motorcycle at a time so be careful.
Deadwood is also right there if you like to gamble and you can spend the night there.
The Needles is only about 14 miles if I recall correctly. I am thinking about taking one of my bicycles out also. I am assuming bicycles are permitted on those roads. Ride it on Harley then maybe in evening on bicycle.
Rode it one time and I will ride it every time I go there now. Unreal is pretty much the only words for it. I would not suggest riding a bicycle during the rally as that would be real dangerous for you and everybody else on the road. It's not that wide and passing you could be real tough with all the traffic. Before or after event would be a nice and safer ride.