I have a lot of spare tires for bikes. I can either store them inside my house in the basement or in the garage. I've got a lot more open space in the garage, so that's my preference. However, I live in the northeast U.S. where we get a lot of temperature fluctuation around the freeze point and sometimes temps lower than 0F (which is rare, but happened quite a bit last winter). Is it generally okay to store my spare tires in the garage or should I bring them in the house for the winter?
Very cold and very hot are generally not good. Zinn has written an excellent article on this topic, and notes that Michelin recommends storing in 5C to 35C temperatures.
You should hang the tires, or keep them mounted and inflated. In general you want to avoid UV and ozone (so keep the tire away from a heater, if you put them inside), and store the tires in a cool, dark, well ventilated, dry place.
I'd say just throw the tires in the garage, even though 0 F is below the recommendation of Michelin; I've left bike tires on bicycles outside in the winter at those temperatures, and the tires are fine. Of course, there may be some life cycle reduction, but the risks are tiny overall.