Wear & tear on tires and brakes are normally not covered under extended warranties, with the exception of road hazards/curb rips/punctures/nails...etc. As stated by others, you want to replace the tires with OEM or matching tire sets. You can buy the same tires from tire rack, discount tire or equivalent tire retailers, but they must be put on by an authorized tire installer. If not, you could potentially void your warranties.
You can also save a little bit, by ordering from a outside tire retailer and have the tires sent directly to your dealership for installation. That would be cheaper and not void any insurance coverage.
