pick up an avid caliper. an 8" rotor is going to run you about 30-40 bucks, and an 8"adapter about 15 bucks at a bike shop. thats 45-55 bucks, a brand new avid caliper and rotor and adapter goes for about 60-70 bucks, and is a far better upgrade. or check ebay and for sale forums for just the avid caliper, you can re-use your shimano rotor.