Most chain tire stores, such as Goodyear, have access to a database of tires appropriate for a Ford Mustang. While independent tire dealers may not use such databases, they likely still have a basic chart of the best tire sizes for a Mustang.
AmericanMuscle.com offers a resource for choosing tire sizes for Ford Mustangs as related to safety, handling and sidewall protection. The website offers a tire guide for Mustang vehicles going as far back as 1987. Older cars are considered classics and have different considerations for their tires.
Three numbers are associated with tire size. The first number states the width of the tire in millimeters. The second number is the ratio of the sidewall height related to the width. The third number gives the diameter of the rim in inches.
Some Mustang owners like to choose a different tire size than recommended because it affects the overall look of the car. When upsizing a tire, owners should change the aspect ratio accordingly; in this case, decreasing the ratio. Decreasing the ratio gives a wider contact path to the wheels and tires. The wider contact path improves cornering ability and makes the car safer to drive while still giving the tires an oversized look.
Wide tires give cars a drag look. Mustang owners shouldn't choose an over-wide tire unless it is specifically branded as a "drag tire." Doing so not only reduces the tire's life, it also makes steering and handling dangerous.