Choosing the perfect tire pressure for racing cyclocross is a very personal thing, with variables in riding style, experience, set up and conditions all affecting the ideal amount of squish in your ride.
As a general rule, your correct tire pressure should be low enough to provide the maximum tire contact area possible and the highest degree of shock absorption without bottoming out on the rim. So what PSI is that, exactly? You will have to experiment to discover what works best for you. Here's how.
How to start experimenting with your tire pressure
The first step towards unravelling this mystery is to establish benchmarks. Either get a good gauge (more on that later) or at least commit to using the same pump all the time, as different pumps can have wildly varying readouts.
Now, start at a fixed point. 50psi is a good point to begin if you’re new to ’cross and using clincher tires. Next, make some notes as you ride and race. Then, adjust the pressure according to the points below — and keep track of the exact pressure and the results.
Pinch flat during a training session? Add some pressure. Feel like you’re getting rattled around like a pinball? Let a little out. But above all, keep track of what you’re doing and how it works.
It might sound complicated, but it doesn’t take long to accumulate some experience and build a good data set. It's also important to remember that what works well for one rider might not be best for another.
Things to consider
Weight: If you weigh more you simply need more tire pressure to create the same tire footprint as a lighter rider. You can’t fight this one, it’s physics, but you can mitigate against it; see Riding style below.
Riding style: If you are new to ’cross you are more likely to make more mistakes and ride rough or harsh instead of light and smooth. With experience, riders typically get lighter on the bike and learn to unweight and float over rough terrain. Subsequently, they can ride at lower pressures.
Gauge: If you use any old gauge on a pump, or don’t use the same one all the time, there’s no way to ensure your baseline of pressures is reliable. Get a good, decent quality gauge and use it for everything. Once you get a feel for different pressures and different conditions it’ll become much easier to make informed decisions.
Wheels/tires: This one is easy. Clinchers with tubes can pinch flat, so they need more pressure. Clinchers with latex tubes are slightly harder to pinch and ride better. Tubeless clinchers ride nicely and can go to lower pressures, but may eventually burp. Tubulars are the best by far, they are very flat-resistant and have an outstanding ride quality. Different tubulars require different pressures depending on casing suppleness and construction quality, but that’s a whole other story.
Local conditions/course conditions: Once you get a hang of what kind of pressures you can ride you can then start making adjustments based on local conditions and course types. For instance, rough, rocky and dry courses may require slightly higher pressures so your rims don’t get beaten up. In areas where the courses are smoother or muddier, riders can go lower.
Weather: Same as above. Once you have your baseline numbers, adjustments can be made for weather. Generally as the weather gets worse, overall speeds go down and lower pressures can be run.
If this is all too technical for you, there is always the old-fashioned thumb test.
Stand over your wheel, place your thumb across the tire and the palm of the other hand over it. Push down until you either lift yourself off the floor or feel the rim under your thumb.
‘Correct’ pressure here would be touching the rim right as you’re lifting onto your toes. This method works in a pinch but doesn’t take into account the variables of tire choice, riding style, the course or weather. Still, you can use this as a very rough gauge — just pay attention to the results and adjust from there.