Why Run Low Mountain Bike Tyre Pressure
As the contact point between your bike and planet earth you need your tyres dialled in correct. The pressure that you run has a dramatic effect on how your tyres, and therefore, bike will perform.
A common mistake is riding off-road with tyre pressure too high. Experienced and pro riders will tell you that a lower tyre pressure is usually the way to go in MTB. Tradition used to dictate that higher pressure equals greater speed but that is now regarded as an out-of-date view, even when it comes to road bikes.
Today, we will shed some light on this topic and discuss the when and the why of low tyre pressure.
What does low mountain bike tyre pressure actually mean?
How many PSI is considered "low tyre pressure" will depend heavily on the volume of the tyre - and to some extent the weight of the rider, as well as if you are running inner tubes or have converted to running tubeless.
Each tyre has a range of recommended pressure, e.g. a 5-inch fat bike tyre may range from 4-7 PSI, while a narrow road tyre may require 90+ PSI. For mountain bikes, the range is usually 15-30 PSI across different widths of tyre.
Your tyres will often have a min and max rating on them but this is a large range and you need to factor in weight, riding style and terrain to find what works best for you within the recommended range.
Why low mountain bike tyre pressure?
The primary benefit of lower tyre pressures is allowing a tyre to use its tread and conform to the trails surface, achieving the best grip levels. Comfort levels also will undoubtedly increase on lower tyre pressures with further smoothing out of trail bumps and features like a bit of extra suspension, a comfy rider generally goes faster!
A lower tyre pressure allow the tyres to deform and grip onto rocky, rooty and loose trails as they can fatten out and make more contact onto the trail surface. You will also get greatly improved grip on corners and when braking when there's more forces acting upon your wheels.
If you are running your tyre pressures too hard you risk 'pinging' yourself off of rocks and roots and generally making for a more unpredictable and uncomfortable ride.
Less fatigue = more energy
With improved grip, less mental fatigue, fewer crashes, and more trust in your bike, low tyre pressure can help to conserve energy.
Vibrations from the ground, through your tyres and your body, causes muscle friction and heat. This all results in wasted energy which can add up over the day. Low tyre pressure reduces these vibrations and in turn, results in less fatigue. Coupled with increased grip, you get further benefits to your riding.
Is low bike tyre pressure always better?
While lower tyre pressure is recommended in many cases, finding a balance between speed, grip and performance is the key to choosing a pressure that suits you. There are no solid rules here, do not be afraid to tweak and find what works for you. Conditions also dictate - in wet slipply conditions, the grip gained from lower pressures is beneficial.
A key benefit of making the swap to running your tyres tubeless is that you can safely run much lower pressures than you can with inner tubes. The average tubeless tyre has stiffer sidewalls than non-tubeless tyres. There is a huge variety of casings within individual models of tyre - thinner casings will require more pressure in order to support the sidewalls of the tyre.
With too little pressure in your tyres you'll feel the tyres squirm in corners and you'll feel the impact of roots and rocks pushing through the tyre to the rim. Your risk of snakebite punctures increases. Lower quality tyres are especially susceptible.
Many riders prefer to run the front tyre a little softer than the rear. This adds a little extra grip to the front of the bike while keeping the rear firm for putting the power down. Typically on a mountain bike tyre, the average rider will benefit from running 2-3 PSI less in the front.
Our suggested starting point for a 80kg rider running tubeless 2.4 tyres is to start out with around 25 PSI in the rear and 23 PSI in the front. Make small changes of 1-2 PSI at a time with the use of a pressure gauge - ideally a digital one from brands like Topeak or Lezyne. Ride the same section of trail with different pressures so you can feel the difference. Terrain dependent you may find you can drop a little more without losing support in the corners.
If you're running narrower tyres and/or riding with a more XC focus then you will find a slightly higher starting point beneficial.
Taking it further with mountain bike tyre inserts
In recent years we have seen enduro and downhill riders start to fit tyre inserts such as Cushcore. These inserts provide extra absorption from trail vibration, extra stability from tyre roll or squirm as well as some extra protection from flats. Due to the reduced volume inside the tyre they make it possible to run extremely low tyre pressures. At bike parks and trails using an uplift where pedalling is less of a concern you will find riders running pressures as low as 15-20 PSI. Inserts are especially popular with those racing as the benefits increase when riding aggressively. In the event of a puncture the support offered by the insert will often let you complete your run.