A good set of all-terrain tires changes how your truck handles the dirt, but running on bald rubber is a gamble you do not want to take. Maintenance costs add up fast when you factor in mounting, balancing, and alignment, so keeping an eye on the total bill before you hit the shop is just part of owning a truck.
You want to time your purchase around holiday sales events like Memorial Day, Labor Day, or Black Friday when retailers drop prices on rubber. Separate the tire negotiation from how you pay for them, because locking in the lowest price on the hardware comes first, and the financing is just a tool to smooth out the cash flow.
That 0% window is a deadline, not free money, and any leftover balance when the 18 months ends will trigger standard interest charges on what is left.