Mounting on the side would be much easier, however the maximum load on the sides is 18kg
Maybe just mount the spare tyre, not the wheel? Justification:
1. Tyre is < 18Kg
2. Tyre is custom, whereas tyre filters are common
3. If you really wanted luggage as well, a circular bag inside the wheel would work.
Would work on the side blade or on the boot/trunk.
Not sure I would want the weight of a spare wheel on the back without some reinforcement and/or custom mount. Over the bonnet would also need a custom mount, but given the high seating position would not cause a visibility issue
