Mine go through spells - I'll replace 'em a few times in one year, and then get 2 whole years of life. They aren't that expensive, just a hassle to change so I don't really worry about it.

1998 Silver Frost SVT Contour born on...8/28/01[/i]
American Iron Shootout Radial Tire 2 Class Champion, Cecil County Dragway April 20, 2002