The tide is turning a little in the bike industry and brands are listening to consumers then building designs around their desires more than ever. An excellent example is the adaptation of disc brakes in the cyclocross and road segments.
With new designs; even if it's merely an adaptation like adding disc brakes to these segments - new issues are bound to arise and new techniques are developed to deal with them. It is no different here and there are some great ways to get your brakes working well and ready for race season - even if you're not immediately familiar with the nuances of disc brakes on a cyclocross frame. Let's start at the beginning:
Correct Installation is Key: Just as it is with any other bike part - but disc brakes have a smaller margin for error than other brake systems. Not to call them finicky; but the clearance between the pads and rotor are generally closer than with other brake systems. If your desire is to have no pad rub on the rotor - starting with correct positioning of the calipers is the key. Some systems are easier and more forgiving than others depending on what level of adjustment they allow on the posts, but none-the-less this is a place to take your time or trust a professional.
Part of the secret here is also the selection of your calipers. Some allow for adjustment of the inboard and outboard pads - providing some fine-tuning beyond lateral adjustment of the caliper on the posts or shimming your rotors (which we'll talk about next). Finding a caliper with adjusting bolts or wheels (like in the case of the Avid BB7) on the inner and outer faces of the caliper is a good visual cue that these will offer more adjustment.
Position your Rotors: On occasion; all the adjusting of the calipers in the world won't provide a desirable relationship to the rotors. Additionally; if you are the type to take spare wheels to a race you may find that the different hubs position the rotors in slightly different places relative to the caliper. Fine tuning your rotor position relative to the calipers will make wheel changes quicker and less problematic.
My suggestion is to try all the wheels you plan to use in the frame you are setting up. Identify the wheels where the rotors sit furthest outboard - farthest from the hub - and set your caliper position to those wheels. From there; use some 0.2mm disc rotor washers or shims (available at many bike shops' service department) to position the other rotors in a similar spot relative to the caliper. This will take some time and possibly a little trial and error; so be patient because it is worth it.
Straight and True: In a perfect world your rotors are perfectly straight and true all the time. However, we haven't discovered that world yet and so your rotors are likely to have a small wave in them or their interface with the hub is not perfectly parallel to the caliper. Additionally, harsh braking with vast changes in rotor temperature can cause the rotors to warp slightly. All of these will cause the rotors to "wobble" relative to the caliper when the wheel is spun.
Regular readers know I'm big on having the right tools; and here is no exception. Don't go at this with your channel-lock pliers; folks! A rotor truing tool like Park Tool’s DT-2 Rotor Truing Fork is the tool for the job and a worth while investment. Again here; take your time. It is possible to get over-zealous and make a rotor worse. My suggestion is to possibly use an old set of rotors to practice on until you've honed your technique before working on your good rotors. The other thing to remember: because of the likely imperfect alignment of the hub shell to the caliper I mentioned above; once you have trued a rotor it will likely only be straight relative to that hub and that position on the hub. So don't expect to move rotors around from wheel to wheel and get similar results.
Choose your pads carefully: Disc brakes often come out of the box with what is the most economical pad the manufacturer makes or sources. Often a steel-backed pad with sintered metal braking surface. The backing material is mostly a matter of weight; but bears a little influence over the system's ability to dissipate heat. Pad material though is where a lot of the magic happens and you want to choose based on your desired characteristics.
As with much of my advice here; my first suggestion is to talk with your local shop about what works best in your climate. Generally though; an organic pad will be the quieter choice with the better braking response but not last as long as the noisier and less responsive metallic pad.
Send 'em to Bed: Ooooh, important final step. People often remark that disc brakes aren't as powerful and responsive as they had expected when they have their initial experience. Just like automotive brakes; the purpose for this is that the pads and rotors aren't "bedded". This is an important "break-in" step that is best done purposefully as part of your final set up for best results.
My preference for this step is to find an open downhill area - especially on a very quiet street or parking lot - which will allow you to carry some speed and the brake over a distance. Build up some velocity and the apply the brakes - slowly but deliberately at first then building intensity - until you're at full braking force over about 10-12 seconds. This builds heat in the system and beds the pads and rotors. I like to do this 5-10 times depending on the response I'm getting with about a minute between cycles (just long enough to climb back up that hill...). It's possible to do this on flat ground if you have an area you can build up to a full sprint and get 10-12 seconds of braking; but you may have to repeat it more.
This all should help you get more performance out of your brakes and enjoy them better. If you've been riding them for a while with lack-luster performance; try starting over with some new pads and possibly new rotors. Your calipers may not be the issue; but is often the first place we look to place blame. As you can see from the steps above; the steps you take to set up and break in your system can be just as crucial as your initial caliper and system selection.