How Much Air To Put In A Mountain Bike Tire (PSI)

I've been asked quite a few times by a number of people how much air pressure to keep in your mountain bike tire for cross country riding and racing. The answer isn't so black and white. There are a number of factors to consider and most of them depend on the current conditions of the single track.

I never ride with more than 45 psi and never less than 30 psi. If I'm riding on hard packed dirt or pavement, I'll ride a higher psi because the higher the psi, the lower the rolling resistance. However, if there are a lot of rocks and roots or the course is muddy, I'll lower the pressure in the tire to increase the amount of traction. There are a few things to consider that will eventually be common knowledge after one has ridden a lot. Even if the course is dry but has a lot of rocks and roots, you'll not want to have the pressure too high in your tires. The bike tends to bounce a lot in these situations and you'll fatigue faster, even though there is less rolling resistance. You'll have to use your own judgment as to the trade off between the amount of root / rocky sections compared to smooth packed sections of the trail.

Just remember:
High Pressure = Lower Rolling Resistance + More Bounce
Low Pressure = Higher Rolling Resistance + More Traction

Also, it should be noted that I'm speaking about tube tires. Tubeless tires can run at lower pressure without the threat of pinch flats. That's when you hit a root or rock and your tube gets pinched between your rim and the root or rock causing a piercing of the tube.