Ah, a simple, very valid question. But the answer isn’t as simple as we’d perhaps like. In fact the relative complexity of the answer is one of the reasons mountain biking is so appealing. So let’s dive into the not-so-simple answer.

Let’s start with what the most important needs are in a mountain bike tyre: Traction/grip, comfort, puncture resistance, durability and low rolling resistance. Unfortunately you can’t have the best of all of these together. Some sacrifices need to be made…

If you ride long distances on relatively non-technical surfaces like gravel roads and jeep track, then you will be choosing a tyre that’s not too wide, has low rolling resistance, and is quite light. On a tyre like this you can have a little more pressure.

If you ride a mixture of surfaces, including smooth hardpack, stones, gravel, rocks and roots, which is what most marathon races include, then you will be choosing a wider tyre that has moderate rolling resistance but good grip. It will also need have to pretty decent sidewall strength to reduce the risk of sidewall cuts. On a tyre like this you will have a little less pressure.

If you ride mostly gnarly rocky, rutted trails that are technical, then you will be choosing the widest tyre with lots of volume to be able to absorb the big hits. This tyre will need the most sidewall strength, plenty of grip and must have a reasonable amount of pressure. Not too little and not too much.

We have discussed a little more and a little less, but what is the baseline? Here’s a widely accepted guide using a rider that weighs 80kg with clothing and gear: 

You need to take your weight and the type of riding you are doing adjust accordingly. Tyre rim width is mentioned here because it has an impact on the shape of your tyre, which can affect your traction and rolling resistance. 

Increasing your tyre pressure will decrease the rolling resistance because there is less tyre surface touching the ground and adding friction, making the bike more efficient and easier to carry speed.

Lowering your tyre pressure will give you more grip, enabling the tyre to deform better over objects.

For this reason, lower pressures can be more comfortable and provide more insulation from the trail below.

However, too little air can make a bike feel sluggish and can be a recipe for picking up punctures because the tyre can more easily be pinched by the rim.

Ultimately, finding the right air pressure gives you safer, more predictable handling characteristics, while adding comfort and puncture protection to your bike.

You need to experiment with what works best for you, starting with a the above guide. Make notes after each ride and use a decent pump or pressure gauge to see exactly what pressure you are running. Over time, you will work out what is the best tyre pressure for you.

If you’re unsure, speak to one of the staff members at Lynnwood Cyclery for advice.