Unless the car's manufacturer instructs otherwise, a car should have matching tires. Tires for cars with ABS traction control, or four-wheel or all-wheel drive, must be the same size. Otherwise, at the very least, both tires on an axle must be the same size.
Car owners should also use the same types of tires, at least on the same axle, according to ETD Discount Tire. If radials and nonradials are mixed, the rear axle should have the radials and the front axle should have the nonradials. When mixing speed ratings, the higher-rated tires should go on the rear axle, even if the car is front-wheel drive. Tire Rack warns against mixing snow tires with all-season or summer tires and mixing tires that run flat with those that don't.