You really can't put a milage on them , I'm knocking on wood as I type this, but my Denali has 130k on it and I'm on the originals , replaced a buddies on his Duramax 3500 with 80k . Lifted jeep will eat'm in a year..... It all depends on the quality of the bearing, the quality that was put into the install and driving style and abuse..... I would think on mommy's minivan you could expect 100+k out of a set short of her jumping parking stops for sport !! .....
