Perfect tyre pressure for cyclocross is a personal thing, with variables in riding style, experience, setup and conditions all affecting the ideal arrangement. Correct pressure should be low enough to provide maximum tyre contact area and 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.
The first step to unraveling 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, say 50psi if you’re new to ’cross and using clincher tyres. 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 important to remember that what works well for one rider might not be best for another.
If you're serious about getting your tyre pressure dialed, then invest in a good gauge
Building a data set can save time when training and racing. But after all the measurements, tests and pre-rides, it still all comes down to feel. The tyre should have maximum traction and shock absorption without bottoming out on the rim, and you should be able to corner aggressively without the tyre collapsing and scrubbing sideways.
THINGS TO CONSIDER
Weight: If you weigh more you simply need more tyre pressure to create the same tyre 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, learn to unweight and float; subsequently, they can ride lower pressures.
Gauge: If you use any old gauge on a pump or compressor and don’t use the same one all the time there’s no way a decent baseline of pressures can be set. Get a good, decent quality gauge and use it and only it for everything. Once you get a feel for different pressures versus different conditions it’s easier to make smart decisions.
Wheels/tyres: 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.
Proper tyre pressure means maximum traction and shock absorption without bottoming out on the rim
Local conditions/course conditions: Once you get the hang of what kind of pressures you can ride, you can then start making adjustments based on local conditions and course types. For instance, here in Colorado the courses tend to be rough, rocky and dry. More rocks means a psi or so more so 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 techie for you, there is always the old-fashioned thumb test: Stand over your wheel, place your thumb across the tyre 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 tyre, rider, course or weather. Still, you can use this as a very rough gauge — just pay attention to the results and adjust from there.
The thumb test is the most basic check you can do — but also the least accurate