Tires are slightly taller ( 1/4 inch per side) and slightly wider ( about 1/4 inch per side as well). One size bigger usually fits fine, and will usually correct optimistic factory speedometers a little.
Most speedometers read a little bit high, meaning an indicated 60 mph is usually about 58 to 59 mph actual speed. The taller tire will correct this somewhat, depending on how much taller the tire is, and how far off the speedometer is.
IF the cars speedometer is dead on, at a true 50 mph the taller tire will show an indicated 49 ... at a true 100 mph, 98 mph on speedometer. Nothing to worry about.