Working under the obvious assumption that they aren't simply flying these bikes directly from world to world, do we know what they use for transportation? Clearly they would need something capable of transporting not only them and their bikes, but presumably a cargo container as well. But the movie doesn't appear to address this.
They travel aboard a (hyperspace capable) carrier ship called the Aerie, according to the Solo: A Star Wars Story The Official Guide
"Enfys Nest leads the Cloud-Riders on strikes. The nomadic group travel aboard a carrier ship, the Aerie.
The ship rarely lands, since the swoop bikes can launch from altitudes of 400 kilometers."
An alternate answer from an alternate universe. ;-) The Art of Solo: A Star Wars Story concept art book introduced the Buckshot as the vessel that carried Enfys Nest's Cloud-Riders from planet to planet. The ship was specifically designed to fire out the speeder bikes, and it was originally planned to be used in the train sequence. Unfortunately, the idea never made it to the big screen, and the ship was only later re-introduced as the Aerie.