First of all Welcome to the forum.
The tire on the back is a metzler 280. You can do any size up to 280 to use the stock warrior parts. Its a kit fabricated by one of the vendors on the forum, there are several on the forum. KyleNV was the one that did this one for me, everyone on the forum can vouch for him. The conversion uses all OEM parts to get the fat tire for the Warrior. You have to send our cores; swingarm, Rim. They are hen widened and sent back to you completed. You then use the OEM hardware to mount them, rear rotor, brake calipers, rear pulley, axel and drive belt. He does provide a spacers for the rear pulley. Installation is not too hard because the swingarm is easy to disassemble. There are several options also (weld grinded off, hidden brake caliper, color for powder coat and so on). If you decide to go with Kyle let him know I sent you. LMK if I can assist you in any other way.
Regards
Randy