How much air should I put in my tires?
New cyclists often don’t give much thought to the topic of tire pressure. When they go to inflate their tires, the primary concern is whether or not the tire has enough air in it. Bicycle tire pressure actually has a significant effect on things like ride quality and handling characteristics. Optimizing the pressure inside your pneumatic tires to suit the type of bike you ride, where you ride it and how you ride it is important to getting the most out of your bike. In this article we explain the basics of tire pressure and tell you how to put the right amount of air in your tires.
Understanding air pressure units
There are different units used to measure air pressure. For our purposes in this article, we’re going to use Pounds Per Square Inch (PSI), which is the most commonly used in cycling. You may see other units being used, like kilopascal (kPa) or bar, but converting to PSI is easy.
What air pressure for which type of bike?
Different types of bikes have different tire pressure needs. The narrow tires on road bikes typically require much higher pressures than the much wider mountain bike tires. Those different pressure requirements are not only a result of the difference in tire sizes, but also reflect the different riding applications these bikes are used for.
To maximize speed on smooth tarmac, road bike tires need to minimize rolling resistance, and thus need to be inflated to high enough pressures to make them firm enough to roll fast with a small contact patch between the tire and the road.
By contrast, mountain bikes are ridden on rough terrain and need to maximize traction in loose and uneven terrain conditions. This means that the tire contact patch needs to be large enough for it to conform to the irregularities on the trail and allow the knobby tread to bite into the ground.
General pressure guidelines by type of bike are as follows:
- Road bikes with 25-28mm tires, 90-120 PSI
- Mountain bikes with 2.0-2.5in tires, 15-35 PSI
- Gravel bikes with 30-45mm tires, 25-40 PSI
A note on maximum 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 optimal way to get the best performance out of your tires. It takes a bit of experimentation to find the sweet spot, as we discuss below.
Factors that affect optimal tire pressure
There are five main factors to be considered when determining the optimal inflation pressure for your bike’s tires:
- Tire type
- Tire width/volume
- Rider weight
- Terrain
- Tubeless vs tubes
In general terms: lower air pressures are good for wider tires, lightweight riders, smoother roads/trails and tubeless tires. Conversely, higher pressures might be needed when running narrower tires, when using inner tubes, with a heavier rider or when riding particularly rough terrain with a higher risk of pinch flats.
When experimenting with different pressures, having a tire pressure gauge can be very helpful. A gauge will give you concrete pressure numbers you can record and refer to if/when you have a flat tire or have to deflate your tires for periodic maintenance. The pressure gauge doesn’t need to be very accurate, it just needs to give consistent pressure readings.
Finding the sweet spot for tire air pressure
A simple method to find the optimal PSI for your tires is to inflate your tires to their maximum recommended pressure, then go for a ride. Observe how handling characteristics change as you drop your tire pressure by increments of 5-10 psi. At very high pressures, you will likely notice that the ride quality will suffer. Riding over bumpy roads will feel too harsh. On mountain bikes, you will experience worse climbing and braking traction. By the same token, at pressures that are too low, you might experience sloppy handling and there will be a much higher likelihood of pinch flats or even tire carcass damage if you ride rough terrain. With some patience, you are going to find the sweet spot for your tire air pressure. If you ride more than one kind of bike, it goes without saying that you will need to repeat these steps accounting for the factors we have mentioned in this article.
