What you Should Know
Selecting tires for cyclocross can be daunting for newcomers. There are so many options -- how are you supposed to know what to choose? Here we'll run through the thought process of how to pick the right tire for you.
The right tire for the right conditions
Most tire makers are going to label their tires for a specific purpose. The three general types of cyclocross tires racers concern themselves with are mud tires, all-purpose/general-use tires, and semi-slicks.
Many people starting out are going to choose the all-purpose tread pattern because they are decent in many different terrains (though they may not excel in most). Most bikes that I've seen come with dry conditions tires, so if you have a new cross bike, you may want to look at getting some new tread before you start training for cyclocross in cross conditions. All-around tread patterns vary widely, but they tend to have decent corner blocks for turning corners, a tighter and/or low center tread for fast, straight line rolling, and they usually have many "working edges."
Mud tires are exactly what the name implies: they are designed for riding in mud. They are meant to grab modest amounts of soil so you can pedal through the slop but also tend to have an open tread pattern with widely spaced knobs to shed the mud. If the mud packs into the tread blocks, traction is greatly reduced.
Semi-slick tires, often called file treads, are for dry conditions where tons of grip is not absolutely necessary. They are very fast and feature micro-knob treads to create a lot of small working edges to grip the ground, but they do not have enough depth to dig in if things get soft. These tires are good for grassy courses or gravel roads. Some will have larger corner blocks -- similar to what the all-purpose treads have -- to allow better penetration of the soil, since corners are the first places to get chewed up and become soft in a cross race.
Semi-slicks are not good at all in mud, and even a slight wetness could decrease your confidence in them enough to elect to go for a more aggressive tread pattern.
If you can have only one set of tires...
As mentioned before, many people will choose the all-purpose as their only tire if they can only choose one. For beginners, it wouldn't be a bad idea to get a mud tire instead.
You will have better grip on most terrains, and you're not giving up much in terms of rolling resistance. Pavement or other very smooth surfaces is where they are not great (though they’re still decent).
Think of it this way, if you gain five seconds on a straight, fast section using all-purpose tread but slide out and crash in a corner, how much time have you really gained if it takes 20 seconds to get back up and riding again?
Semi-slicks should never be your one and only tread, as they are limited to dry conditions. If you choose only semi-slicks and it's wet and muddy, be prepared to slide and to run through the muddy stuff. Unless you live in a very dry climate and you only race golf courses, these should not be your go-to tread pattern for racing.
Tubes, tubeless, tubular... What's going on?
Okay, so you've been reading or talking to people and have discovered there are options other than just regular clincher tires. It can be overwhelming if you get stuck in the mentality that you have to have the best, so listen up.
First, you can race with any of these types of tires. They all have their advantages and disadvantages, but they all work, and all of them are used for racing.
Second, in cyclocross, tire pressure is very important. A small difference in psi can make or break a race. Changes as small as 10 psi can make you feel like you're riding around on ice or cornering on rails.
The bike tires that everybody has, these are, by far, the most common tires you will see among beginners and maybe even into the intermediate categories of racers. They are cheaper, more convenient and very easy to swap when you need to adjust for course conditions. The big disadvantage of clinchers is pinch flats. This limits how low of a pressure you can run with the tires. Another downside is, due to how they are constructed, you are unable to get the same tire suppleness and ride quality that you can with a tubular or tubeless setup.
Tubeless 'cross setups give all the same benefits of clinchers with only a little more hassle. At the time of this writing it is still fairly new to cyclocross and hasn't been readily adopted. The reason being is that most people willing to deal with setting tires up to be tubeless are willing to set up tubulars, which are much more available since they've been around much longer. The advantage is this: tubeless tires can't pinch flat because there's no tube. However, you can burp the tire or have the tire come off the rim if the tire and wheel are not friendly with each other.
While some may not agree, tubular tires are the best option if all you care about is performance. Most, if not all, pro racers use them -- many even using only a few select brands, Dugast being one that is highly sought after (some pros say they will only race Dugast tires). My point is, pros race what they are the fastest on, so if they're all running tubulars, there's probably a good reason why.
Tubulars kind of go hand-in-hand with cyclocross, like mud and broken bike parts. They allow for very low pressures, and the tire construction allows a very supple ride that can't be matched by clinchers. You also can't pinch flat because of the way the tires are made.
One might ask, "If they're so great, why doesn't everyone use them?"
Tubulars are like race cars, they offer up increased performance, but they also require more maintenance. Tubular tires requires tubular rims, since the tire is glued to the rim. The gluing process can be frightening for newcomers to do on their own and is much more time consuming and more difficult than mounting clinchers. The tires are also more delicate, due to their suppleness. Some can be damaged by water over time as the tire’s casing can rot.
Also, since the tires are glued to the rim, you will need multiple sets of wheels instead of just a quiver of tires in order to have multiple tires choices on race day. Many people will train on clinchers and then race tubulars to keep from wearing the tubulars.
As mentioned earlier, tire pressure is very important in regards to how the tires perform. Too high and you will lose traction and could experience an overly harsh or bouncy ride. Too low and you could pinch flat (if running clinchers), damage the rim, decrease high speed traction, or you will experience high amounts of rolling resistance.
So how much is enough? It all comes down to trial and error. You need to practice with what you will use to race. For clinchers, you'll be looking at the 40-50 psi range. Tubeless will be down in the 30-40 range, and tubulars are often below or around 30 psi. Theses are just reference points, of course, as pressures depend on the course conditions, the rider's weight and riding style, and the tires themselves.
Typically, the more you weigh the higher pressures you need to run. The softer the terrain the lower pressures you should run to get traction. If you are good about choosing race lines to avoid bumps and hits, you can take a little extra risk and run lower pressures, but if you are a “basher” and just pedal through and over anything and choose not to finesse over bumps, roots, etc., keep a little more air in the tire. This last part also goes for remounting the bike; if you plop onto the saddle when remounting, you might want a few extra psi in there.
For tubulars, my general rule of thumb is to lower the pressure to the point where the rear tire feels like it "wanders" on pavement. Usually this means it will grab the softer terrain of the race course pretty well. Lower the front psi accordingly; it should be lower than the rear by about 10 percent, but mess around with it a little to see what works for you. Even with tubulars, you don’t want the rim to be contacting the ground as it can slice tires and damage rims.
A final check on race day should always be done. Take a hot lap during warmups and see how the tires behave. If you are bumping the rim, add some air. If you are sliding through a lot of corners let some air out. Many courses are going to have spots where you want lower pressure for one section but need higher pressure for a different section. You have to decide which part you want to target as a spot that will improve your overall lap time. You may have to deal with decreased traction to run higher pressure or ride a little more cautious in a section if you run the pressures lower.
Wheels also have an effect on how the tires perform. Since cyclocross is an offshoot of road racing, a lot of the components are the same, wheels included. The problem with this is that you run wider tires in cyclocross, but you might be using the same wheels designed for the road. While this can be done, ideally you want a wider rim for a wider tire.
Wider rims are becoming more popular these days and some manufacturers are starting to make rims with cyclocross in mind instead of having a rim for the road that is acceptable for cyclocross. The wheel, spokes, hub and tire are all part of a system that links the bike to the ground. Tires and wheels are the single biggest equipment improvement you can make for CX, to the point that the pros will have several sets of wheels and tires so they can tailor the wheels and tires to the course.
Tread pattern, tire type, wheels, and air pressure all come together to make a complete system that is of big importance to traction and ride quality. Think it over, talk with other riders, and talk it over with the guys at the bike shop. See what has worked for them and use that as a starting point for finding the setup that works for you. Happy riding.