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In this situation, I would suggest that you consider:
- Have the wheel bearing repacked, and this should include a brake check-up while the drums are off the axle. Properly greased bearings and functional brakes are critical safety measures with a single axle coach.
- Your coach would have originally been equipped with Load Range C 15" ST tires . . . most likely . . . . ST 205/75R15 . . . or ST 225/75R15. Either size would likely fit your coach, but clearances can be tight on the single axle coaches.
- The specifications for the wheels on your coach are likely the same as other Airstream coaches, and those specifications would be:
- 15" x 6" wheel with 2,600 pound or greater weight rating.
- 6 lugs on 5.5" centers
- 4.25" center bore
- 0.0 offset
You can learn more about the specifications for your coach on this link
Since you know little about the age of the tires, a new pair of tires would be a cheap insurance policy along with new metal valve stems. Any blowout on an Airstream is potentially very expensive particularly if the tire doesn't remain in-tact. Blown tire shrapnell can seriously damage your coach to the tune of thousands of dollars . . . so new tires are a comparatively inexpensive insurance policy. Sometimes, trailer tire specialty shops will offer special deals on trailer tire and wheel combinations . . . or, your local tire dealer will likely have sources where he can source trailer wheels as well as tires.
Good luck with your coach!