Plus-sizing in the tire industry is the growing practice of replacing a vehicle’s original equipment wheel size with a larger diameter wheel and replacing the tire with a lower-aspect-ratio tire of the same diameter. This practice is normally associated with aftermarket sales, and there is a growing trend for vehicle dealerships to fit these larger wheels/tires to new cars. This paper discusses the general practice and its effect on some of the performance characteristics of vehicles. A vehicle taken from the NHTSA New Car Assessment Program’s rollover “Star” rating program is used to illustrate the impact of plus sizing on static stability. Some of the dynamic tire effects that could influence vehicle stability are discussed, and preliminary testing data on the dynamic impact of plus sizing are presented.