Ive bought tires from TireRack.com twice, in fact UPS just seconds ago delivered me a tire, had to replace a tire that went flat on me last week and couldnt be fixed, they orginally were ordered by Southern Tire when I bought 4 tires and whereever they ordered from didnot have the General tire I needed and it was on back order, at least 2-3 weeks before it would come in. I went home and checked TireRack and they had the tire in stock.
After paying for the tire ,shipping, and having someone mount and balance I really dont see where you save alot of money buying online.