Are you required to get city approval and permits for your ride? If so, then you will also be required to have event insurance. If this is a non-public (ie limited to a bike club or something) ride that you are organizing then you should be OK. No waiver is fool proof. But laws in different states and counties apply. I'm in California. Generally, insurance in some form is required to hold an event of that nature. Your broker and attorney should be able to provide the right advice.