something like “It would make me really uncomfortable with you bringing the motorbike on our trip. I want you to have fun, but i really don’t want you to get hurt and i hope you can see where im coming from and understand stand that” he should be able to understand where you’re coming from and if he doesn’t, and brings it anyways then that’s on him. you communicated how you felt
NTA, It sound like you’re stressed about him getting hurt and a trip to the ER which is an instant vacation killer - especially if he gets seriously hurt. It great everyone wants him to have fun, but it’s both of your vacation and it can be hard to relax when you’re stressed about where the Hubby is. Maybe he can plan a different vacation/ bike trip with his friends? That way he can still enjoy his bike but you’ll get some rest.