1974 Argosy 27 foot - Tire question
There is a lot of info available about tires. My 75 had 7.00x15 light truck tires on it. The oldest of which by the DOT numbers could be original or from 1985 no way to tell for sure, the newest was from 1999; all with good tread, no cracking and holding air. The 7.00x15s were 27.88" in diameter. Due to signs of tire damage on the lead edge of my wheel wells, I replaced the antique/vintage tires with 205/75-15 trailer tires which are 27.1" in diameter. 225/75-15s are 28.1" The original tires were load range C, so the new ones were also; load range C rated at 1,820 pounds each, so 7,280 pounds total and the GVWR of the trailer is 7,000 pounds.
The general guidance from the tire industry is tire lifespan is anywhere from 3-10 years depending on the source you read and even more dependent on whether the tire is under load and subjected to UV light. Tire warranties are typically 4 years from purchace.