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Beginner cyclists often don’t give much thought to the amount of air that should be in their tires. What matters is whether or not the tire has air in it, and if it does, the bike is ready to ride. Bicycle tire pressure is, in fact, a rather complex topic and having the right pressure for not only the type of bike you ride, but also the kind of tires you use and terrain you ride on is critical for a good ride quality and handling characteristics. In this article we explain the basics of tire pressure and tell you how to put the right amount of air in your tires.
What units do we use to measure tire pressure?
When we talk about air pressure, we have to first define the units of measurement we use. While there are various units used to denote air pressure, the most common in the cycling world is Pounds Per Square Inch (PSI). You may see other units being referenced, like kilopascal (kPa) or bar, but for the sake of simplicity, we will only use PSI here.
Different pressures for different bikes
Different types of bikes have different tire pressure requirements. The skinny tires of road bikes typically require much higher pressures than the higher-volume mountain bike tires. The different pressure requirements are not only a result of the different kinds of tires, but also a reflection of the different types of terrain these bikes are ridden on.
Road bike tires need to have the least possible rolling resistance on smooth tarmac, and hence need to be firm enough to roll fast with a minimal contact patch between the tire and the ground. That’s why road bike tires need inflation pressures between 90-120 PSI (track bikes, ridden on closed velodromes, often need even higher pressures!).
Conversely, mountain bikes are ridden on off-road trails and need to maximize traction on loose dirt, which means that the tire contact patch needs to be large enough for it to conform to the irregularities on the trail and allow those aggressive knobs and protrusions in the tire tread to bite into the ground. Therefore, mountain bikers typically inflate their tires between 15-35 PSI. On fat bikes with even bigger tires (3-4in), pressures can drop to as low as 5 PSI.
Optimal pressures are not maximum recommended pressures
Tire manufacturers often print pressure guidelines on tire sidewalls, and many new riders will often just inflate their tires to the maximum pressure listed by the manufacturer, which isn’t the best way to get the best performance out of your tires. Setting the optimal pressure in your tires takes a bit of experimentation to find the sweet spot.
Finding the Goldilocks zone of PSI
The key things to consider when setting your tire pressure are:
Tire type
Tire width/volume
Rider weight
Terrain type
Tubes or tubeless?
Generally speaking: lower pressures are optimal for wider tires, lighter riders, smoother terrains and tubeless setups. The opposite is true: you will need more pressure in your tires if you run inner tubes, if your tires are narrower, if you’re a heavier rider and if you ride rough terrain.
It really helps to have a pressure gauge when experimenting with different pressures, because then you can have meaningful numbers you can record and use to re-inflate if you experience flats or have to deflate your tires for maintenance. The pressure gauge doesn’t need to be super accurate, it just needs to give consistent readings. Many floor and mini pumps now come with integrated air pressure gauges.
One simple method to experiment with tire pressures and find your optimal PSI is to inflate your tires to their maximum recommended pressure (but don’t exceed that pressure or you risk the tire blowing off the rim!), then go for a ride and decrease your pressure in increments of 5-10 psi and observe the changes happening to the handling characteristics. At max pressure, ride quality will be too harsh and you will feel all the bumps on the road (and traction will suffer especially on mountain bikes). At pressures that are too low, handling will feel vague and sloppy and you may easily get pinch flats. Your optimal pressure will be somewhere in between!