Are you asking about bicycles, scooters, or motorcycles ??
If you're asking about scooters or light weight motorbikes then the VersaHaul brand is great. It plugs into your reciever hitch hole and will carry close to 400lbs. I got one to haul a 150cc Honda scooter, easy one person load/unload. The scooter just stays on the MH, it's a blast to ride too
HTH
Don
PS: No It won't support a Harley
Use a trailer for that.