I love taking women on the back of my bike. I rode for 1.5 years before I took on that responsibility though. The last 3-4 girlfriends I had loved riding pillion. 5 girls ago, that chick hated it, she was terrified and didn't want me going over 35, I only took her out once, she was a nutcase anyway.
My present girl likes riding on my bike but doesn't want to ride her own bike on the road. Meanwhile she's owned 2 250 cc dirtbikes, and owns a quad. She just doesn't want to ride on the road and I respect that. Just means I get her rubbing up on me more often.
I did break the 1 penis per bike rule though. My good friend and coworker is kind of a dumbass and lost his license. In early December my car didn't want to start so I texted him "Bundle up and pack light, we're taking my bike" and picked him up on my KLR. It was a funny site when we pulled into work, and stops were kinda weird because he slid into me.
I lent him my spare Icon helmet that's a medium, fits most women I've dated. When we got to work I told him "Eric you're the first person to wear that helmet that I haven't slept with"
It's fun making him feel awkward, perhaps enough of that and he'll get his shit together and get his license back.