It was easy to ferry winter wheel/tyre sets around when I had a Convertible as they would fit standing up on the folded rear seat, but that doesn't work with a Roadster so here, for your amusement, is my new method - one in the passenger seat, one and a half in the boot and one on the bike rack:
Thank goodness, the bonging from the car saying the boot is open stops after you drive away, but it still bongs once every time you move off after coming to a stop.....