Cyclocross are semi-specialized bikes that look like normal road bikes. They are built a little different though to withstand the abuse of a cyclocross course.
Frame: A true cyclo-cross bike is a road bike adapted for off-road use. When shopping for a frame, weight should be a primary consideration. Aluminum has carried more riders to victory than any other frame material. But it is less durable than steel, so don’t count on using the same frame for more than a couple seasons. If you decide on a steel frame, get the lightest you can afford.
Choose the same size frame you use for road racing, but with extra seat stay, chain stay and fork crown clearance. This helps prevent the build-up of mud and other debris that can add unwanted rolling resistance. You also need a higher-than-normal bottom bracket to prevent pedals from rubbing against the ground. Water-bottle braze-ons are unnecessary – cyclo-cross races are too short to pack a bottle on your bike, and the bottle would be in the way when you shouldering your bike.
When fitting your ‘cross bike, your saddle height should be 1 cm lower and stem length 1 cm shorter. This allows for more body movement when maneuvering your bike in technical sections.
If you decide to use two bikes – and a spare is a good idea, since cyclo-cross can be hard on equipment. Strive for consistency in equipment. When you have to jump off one bike and onto another, it’s important that your shift levers, saddle and other components be in the same places.
Wheels: Cyclo-Cross wheels should be tubulars, which are light, strong and dependable, which means your tires are less likely to get pinch-flats on rough terrain. Wheels with thirty-two spokes or fewer work on almost all courses. Tire brands to look for are Clement, Barum, Vittoria and Wolber.
Gearing 13-26 cog set should be sufficient (if you need more than a 26-tooth cog, it may be time to start running). Use a high-quality road derailleur or a short-cage mountain bike derailleur. Up front you may choose to use a single chain ring, probably no more than a 46-tooth, but you should run a chain guide to keep the chain on the ring over bumpy sections. If you decide to use two chain rings, a 48/42-tooth combo is standard.
Handlebars and Shifters: Use road-style dropped bars with bar-end shifters. Cut off the tips of your bars – maybe 3 to 5 cm, depending on the size of your hand – which brings your shift and brake levers closer and makes for less space to shuffle between the two. Shift/brake-lever combinations are a good alternative, although they are a little exposed, a lot heavier and can be damaged beyond repair in a crash.
Brakes: Cantilevers offer superior stopping power, light weight and clearance to help prevent debris buildup. V-brakes also work well but require an adapter to work with cyclo-cross levers. Some racers choose disk brakes, which are the ultimate in mud clearance and performance, but are heavier and less common on less-expensive ‘cross bikes.
Pedals: Look for something along the lines of the old Lyotard 460D, which has been the standard in cyclo-cross for years. These aluminum pedals are symmetrical, serrated on both sides, wide, light and inexpensive. Symmetry is important because any pedal becomes unbalanced when you add a toe clip, making it very difficult to flip over and slip your foot in; unbalanced pedals only increase the problem. Double-sided serration is important in case you need to ride on the back side of the pedal; it gives you a good surface with which to make contact.
Some tips: If your foot hangs up on the front pedal plate, attach a small ramp to guide your foot past it (a 2 or 3mm washer slipped between the pedal plate and toe clip also makes it easier to enter the pedal when you first flip it around). Toe clips should be doubled to prevent them from being broken or bent down to the pedal body when stepped on. The toe straps should be made of stiff leather and attached to the pedal on each side with rivets. Attach a plastic tab to help you tighten your straps should it become necessary.
Double-sided clipless pedals, which are common on mountain bikes, are very good and getting better all the time. Some are not effective in muddy or icy conditions, but brands such as Time and Crank Brothers have been proven to perform in poor conditions. They are preferable to clips due to their consistent engagement and release.
Clothing: It should fit skin-tight, especially shorts – you don’t want any loose clothing snagging on your saddle when you’re jumping on and off your bike. But remember, it’s wintertime, which generally means bad weather. Your race-day bag should include clothes that layer well for temperature changes.
Shoes should be made with a soft toe and good traction for running, similar to mountain-bike shoes. If you are using toe clips, look for shoes that accept the old-style slotted cleat, which will help you pedal with 360 degrees of power.
Finally, consider buying (or borrowing) a shoulder pad like those common in women’s clothing to sew inside the right shoulder of your jersey or skinsuit. It will minimize the bruising you can expect from dumping a bike on and off your shoulder.
Using a Mountain Bike: Strip if of all non-essential gear – spare tire, pump, fenders, water-bottle cages, and shocks. Remember, you’ll be carrying this bike, and it should not be heavier than is absolutely necessary. As for suspension, it may be great for the long, steady efforts of mountain biking, but in cyclo-cross, you have to accelerate repeatedly on each lap – which is much easier on a lighter bike with a stiff fork.
The wheels should have as small a tire profile as the rims will accept (1.5" to 1.0"). You should consider adding road-style drop bars and bar-end shifters – this will help you carry your mountain bike more comfortably and allow more hand positions for maneuverability.
One other note: cyclo-cross is a mass-start race, and according to US Cycling Federation rules, bikes used in mass-start events may not have objects that protrude forward. This means no bar ends in USCF sanctioned cyclo-cross races. Remove them before race day and save yourself an unpleasant surprise at the start line.
When using a road bike, consider having a frame-builder add cantilever bosses to your fork and seat stays – cantilevers are a lot better than road calipers for stopping in all conditions. While you’re at it, move your brake and chainstay bridges up a bit to allow for more tire clearance. Don’t forget to swap your road pedals for something more suitable for the rigors of off-road riding.