Using the correct pressure for your road or mountain bike tyres can make a big difference to your comfort and your bikes performance. Inflation guides, often found on tyre walls or packaging, give the pressure needed in PSI (pounds per square inch) or bar (one bar is the atmospheric pressure at sea level).
This is a safety feature; at the upper limit, it is the maximum amount of pressure before there is a chance the tyre may blow off the rim, at the lowest it is how much pressure is needed to hold the tyre in place and prevent it rolling off. However, between these limits, you can tweak pressure for your individual needs and it is always better to know how to do so, as even little tweaks can have a big effect on how you ride.
Road tyres have smaller volume but higher pressure than mountain bike tyres. How hard you should pump your tyres up depends on three factors; the width of the tyre, the load and conditions. You should check your tyre pressure before every ride. When first inflating your tyres, make sure to check the sidewall or packaging for the manufacturer’s advice.
Road tyres come in a variety of widths, 23mm used to be the most common for general road riding and racing, touring tyres were generally wider 25-32mm with hybrids and gravel bikes running tyre widths of up to 30mm-50mm.
However, newer research from tyre manufacturers suggests that a 25mm tyre for road racing is faster so road and sportive bikes are now often spec’d with this width. The wider the tyre, the more volume it can hold and narrower tyres need to be inflated to a higher pressure.
How do I work out the ideal tyre pressure?
The load on your tyres is the combined weight of you and your bike generally speaking for every extra kilogram you carry the pressure should be increased by 1%. Lighter riders on lighter bikes can get away with slightly lower pressures. Change your tyre pressure if are carrying a rucksack or extra weight on your bike.
When should I reduce the tyre pressure on a road bike?
Whilst the general rule of thumb is that higher pressure tyres roll faster, in some conditions you can benefit from reducing the pressure. In wet weather reducing the pressure will increase the contact patch with the road, helping to improve your traction, you only need to reduce it by 0.5 bar or max 10 psi.
A slightly softer road bike tyre will also improve your comfort as more of the vibration from the road is absorbed, ergo your bike doesn’t bounce as much. If you are tackling a rough road surface, or even cobbles, lower pressures help improve traction as there is more tyre in contact with the ground and it will deform to roll over lumps and bumps more smoothly.
With lower pressures there is an increased risk of snake-bite punctures also known as pinch flats. To minimise this risk, run good quality, rubber butyl inner tubes as latex tubes are too fragile. A relatively new development for road bikes is ‘tubeless’ which eliminates pinch flats altogether. Without an inner tube the air pressure is held by the seal between tyre and rim so you can still puncture if the tyre gets a cut or hole in it.
Tyre Pressure for Mountain Bikes
Adjusting your tyre pressure is an integral part of getting the best performance from your bike. Tyre pressures need tweaking and adjusting for every ride, depending on the terrain and conditions.
Should I keep the tyre pressure within the manufacturers’ recommended pressure range?
The manufacturers’ recommended pressure range allows plenty of room for manoeuvre and as long as you stay within the upper and lower limit, your tyre pressure should be safe and not affect the longevity of the tyre. You can run your tyres lower than recommended but it can lead to damage to the sidewalls. Wider rims support the tyre better allowing you to run lower pressure without the tyre folding under you.
Why does changing tyre pressure have such a big effect on mountain bikes?
Your tyres are your contact with the ground. Tyre tread, volume and pressure have huge influence on your grip and traction, to an experienced rider even a few psi can make a difference to how the bike runs. At lower pressures you can increase grip and traction, at higher pressures the tyre will roll faster.
Pressure is related to the combined weight of you, your bike and your pack. The heavier this combined weight the more pressure you need in your tyres. The same tyre pressure might feel hard and lacking traction to a lighter rider, but soft and squirmy to a heavier rider. It is also influenced by riding style, if you ride heavy, slamming into rocks, then you will want a bit more pressure than a rider who rides ‘light’. If you are hucking off jumps and drops, a little more pressure will stop pinch flats and the tyre squirming or rolling as you land.
What else do I need to bear in mind when adjusting tyre pressure?
Terrain and conditions will affect how soft you want mountain bike tyres. Lower pressure provides more grip. On a trail with lots of roots and loose rock a softer tyre will give you better traction, but it is a balancing act between that and getting pinch flats. In muddy conditions a harder tyre can cut through better and when the surface is already soft a low pressure tyre can feel even less secure, which you definitely don’t want.