When it comes to talking about an "extra tire", one may realize that there are multiple synonyms for it. Let's take a look. Firstly, an extra tire is commonly known as a spare tire. The word "spare" implies something that is available in case of an emergency or as a substitute. Another synonym for an extra tire is "emergency tire"; this term also alludes to its purpose of being there for rescue in times of need. If we want to get more technical, the term "donut tire" may be used, which refers to a compact spare tire that can be used temporarily to save space. All in all, there are several ways to refer to an extra tire - but they all ultimately mean the same thing: a back-up tire.