So I built a touring bike with BB7s. While I was readjusting them (its winter and I am bored) I notice the rear rotor is ever so slightly out of true. Seems like a good reason to spend some money so what is the determining factor on what size rotors I use. Can I intermingle brands, say a shimano or hayes rotor. Dont know if it matters but its a Soma double cross frame with the IRD strait blade disc specific fork.