Air down off-road: why lower tyre pressure gets you grip on gravel

What airing down changes

At road pressure a tyre is hard and round. Let some air out and it softens, flattens where it meets the ground, and puts more rubber down. Michelin says it plainly: lowering pressure for some off-road surfaces increases the tyre's contact area, which can improve grip on loose or soft ground.

That's the difference between skating over gravel and gripping it. It matters most on loose gravel, dirt and slush, the stretches where the tarmac just stops.

How low to go: your tyre decides, not a percentage

I'm not giving you a number on this page, on purpose. The right off-road pressure depends on your tyre, your rim, your load and whether you run tubes. Two bikes dropped by the same percentage can end up on opposite sides of the safe line. Start from the road pressure in your owner's manual, come down a little at a time, and follow your tyre maker's guidance over anything posted online. Know the two limits before you let any air out.

• Tubed tyres. Go too low and the tube gets pinched between tyre and rim when the tyre compresses on a rock. That's a pinch flat, and the rim can take damage too.
• Tubeless tyres. Very low pressure can unseat the bead from the rim.
• Either way, check it cold, with a gauge.

Air up when the tarmac is back

This is the half people skip. Mountain routes come in patches: a bad stretch, then a long run of tarmac. Air down for the patch, forget to air up, and you're riding a loaded bike soft at road speed. Metzeler lists what low pressure does on the road: poor handling, a bike that wanders, faster wear and less control. Carry a gauge and a pump that works, and use them at both ends of the rough section.