how often do you need to replace tires
A good time to rotate your tires is when you get the oil changed, assuming you do that at least once a year and more often if you drive, say, more than 10,000 miles annually. Most vehicle manufacturers recommend that the tires be rotated on the same schedule as oil changes. In most cases that means every 7,500 miles or six months, though some have stretched the oil-change interval to 10,000 miles, such as on many Fords, Volkswagens and Toyotas.
Unless you drive fewer than about 7,500 miles per year, you should probably rotate tires every six months or so. The tires mounted on the drive wheels of any vehicle perform extra duty because they apply the power to the pavement.