* Check the sidewall of your existing tires: The tire size (e.g., P245/70R17) is printed on the sidewall. The "17" indicates the wheel diameter in inches.
* Look at your wheels themselves: The size is often cast into the wheel.
* Consult your owner's manual: This will specify the factory-recommended tire and wheel sizes for your specific truck.
* Check the sticker in the driver's side doorjamb: This sticker often lists the original tire size.
Without this information, it's impossible to say definitively what the OEM wheel size was. Common sizes for the 2005 Ram 1500 2WD include 16", 17", and possibly 18" depending on the options.
