If you check out the builds section you may see several alternatives. I don't carry a spare tire but I do carry a portable air compressor and a plug and patch kit. I have never had a flat but we have worked on two quads that had flats because of older weathered tires, they are not that hard to repair in the field.
If you look at the rack system I have one mine its got a tire mount. It was really tight with the 31”BFG’s but its really tight and doesn’t rattle. A HUGE PLUS. I can send you a close up pic if you want.