Русско-англо-русский юридический словарь

A spare wheel is a wheel with a tyre on it that you keep in your car in case you get a flat tyre and need to replace one of your wheels. (Collins Dictionary)

A spare tire is an additional tire carried in a motor vehicle as a replacement for one that goes flat, has a blowout, or has another emergency. (Wikipedia)

The PP would advise Jane to take a spare tire while driving as a reasonable precaution against a flat tire. (Owning the Genome by David B. Resnik, State University of New York Press)