I cycled Beartooth Highway last year. Did about 20 miles from our BnB outside Red Lodge to about a 1/2 mile over the Wyoming line. Really great ride. The grade really isn't bad so not difficult in that regard. But, would take some acclimatization if you're a low-lander. Our road trip also included the Badlands. I got in an early morning ride in the park - more a rolling hill ride than a hill climb. But I really enjoyed the quiet cycling the Badlands.