Have you specifically asked him about the things you indicated that you "don't understand"? If he can't articulate rational reasons for his objections and/or can't admit there's something more to it, then perhaps you should do what Red's boyfriend did and buy the bike. Don't do it behind his back. Rather, just day that he's offered no reason for his objection that makes any sense and that while you wish you had his support, you're not going to forego the purchase. At some point, you do have to just do what's best for you with or without your partner's support. I sure hope it doesn't come to that though.