Meh ...
No need to go thru Casper when there are way better options.
You will have clumps of motorcycles almost anywhere -
but way fewer if you are going around Sturgis by 100 miles or more.
Here are choices from Buffalo to Chadron in western Nebraska:
Section 1 - from Buffalo to Newcastle
Hwy 196 along the Bighorn Mountain Front has great views and almost no traffic.
Kaycee has a small campground, small motel, store, cafes, and bars.
Hwy 192 has light traffic; Hwy 387 has light/moderate traffic and shoulders.
Wright has camping, motels, stores, cafes, bars - modern coal mining town
Hwy 450 through the Thunder Basin has light traffic, remote High Plains scenery
Newcastle has all services.
https://ridewithgps.com/routes/50575087Section 2 - from Newcastle to Chadron
a) Is the best choice. You get the southern Black Hills, Mickelson Trail, and Fort Robinson.
It is the longest of the three. US 16 has moderate to moderate-plus traffic and a few narrow sections.
The backcountry of Fort Robinson is spectacular - far fewer people than the Black Hills.
b) Shorter option that skips Fort Robinson, but includes Wind Cave National Park.
c) Shorter option that skips the Black Hills, but includes Fort Robinson.
US 85 has moderate traffic, good shoulders, poor scenery.
https://ridewithgps.com/routes/50575163https://ridewithgps.com/routes/50575204https://ridewithgps.com/routes/50575346