@boringcyclist are you familiar with the Silver State 508?
Have you ever ridden with Marko Baloh or Shane Trotter? 508 miles in 26 hours (and change) including 22,000 feet if climbing.
The 508 has categories for solo (supported), solo (unsupported, aka "solo rando"), and fixed gear.
I've ridden the two-man and four-man relay categories (31-ish hours).
#SS508 #SilverState508 #EnduranceCycling