Pretty sure the RL570 has a 31.8mm clamp. You'll either need to get a new lever with a 24mm clamp or make a huge shim (which I don't recommend).
Here:
http://bikeisland.com/cgi-bin/BKTK_S...ls&ProdID=1673
Also, if your current bars are 31.8 and you're getting bars that are 26.0, you're either going to need a handlebar shim or a new stem. Post a pic of your current setup.