You need a rack with a dog-legged rear stay like this. http://www.rei.com/product/780549 I have a similar Radical Explorack that cost about $40. With my previous rack I swung the panniers into the spokes several times when making sudden swerves. I now use a trunk bag on top of the rack because I used to carry too much in panniers. I keep the U-lock permamently at work.