ive always heard that it doesnt matter what drivetrain (8/9) you ride, the front and rear derailleurs are "dumb" components. i just got a new frame and need just my derailleurs now to finish it. im planning on stickin with just 8. all discriptions that ive seen for derailleurs say theyre designed for 9 speed systems. does that matter? how do i figure out my clamp size? measure circumference and figure out diameter in mm?