Trail MTB: 23–28 psi front, 27–32 psi rear for a typical 80 kg rider on 2.4 inch tyres. Enduro: subtract 3–4 psi from those numbers. XC race: add 4–5 psi. The width effect is enormous on MTB — going from a 2.3 to a 2.5 inch tyre drops optimal pressure by 4–6 psi with no other change.
Why MTB pressure is different from road and gravel
Mountain bike tyres operate at the lowest pressures of any cycling discipline because the objective is fundamentally different. On road, the primary goal is minimising rolling resistance. On gravel, it's balancing rolling resistance with traction. On MTB, traction and control dominate; rolling resistance is secondary to whether you can maintain speed through technical terrain without losing control or damaging the rim.
At low pressures (20–30 psi), the large MTB tyre casing deforms substantially under load. This deformation is intentional — it allows the tyre to wrap around rocks, roots, and rough terrain, maximising the contact patch and grip. The same principle that makes a wide gravel tyre at 30 psi feel planted also makes a 2.4 inch MTB tyre at 25 psi feel glued to the trail.
The risk at very low pressure is rim strikes — the wheel hitting an obstacle hard enough that the tyre bottoms out and the rim contacts the ground. This can damage rims and causes sudden deflation. The lower bound on MTB pressure is set by rim strike avoidance, which depends on rim width, tyre volume, and riding aggressiveness. Running tyre inserts (foam or liquid) allows you to go 3–5 psi lower by providing a cushion against bottoming out.
The width effect — bigger than on road or gravel
The relationship between tyre width and optimal pressure is exponential, not linear, and this becomes very visible in the MTB range. Going from a 2.3 inch (58 mm) to a 2.5 inch (63 mm) tyre drops optimal pressure by 4–6 psi. Going from 2.3 to 2.6 inch (66 mm) drops it 7–9 psi.
For a reference 80 kg rider, a 2.3 inch rear tyre wants approximately 28–32 psi. A 2.5 inch wants approximately 24–28 psi. A 2.6 inch wants approximately 22–26 psi. If you upgrade from 2.3 to 2.5 inch tyres and don't adjust pressure, the new tyres feel harsh and boardlike — you're running them at the equivalent of a road tyre at 110 psi.
Volume matters as much as nominal width. Two tyres with the same stated 2.4 inch width can have different volumes depending on casing profile and tread pattern design. High-volume "plus-style" 2.4 inch tyres behave like a 2.5 or 2.6 when inflated — measure the actual inflated width at your target pressure if you're unsure. The calculator uses nominal width and is a starting point, not a definitive prescription.
Discipline, hardpack vs loose, and insert tyres
XC cross-country racing prioritises rolling resistance. XC riders typically run 28–34 psi rear and 25–30 psi front on 2.2–2.4 inch tyres — high for MTB, but XC courses are groomed and the speed premium justifies it. Traction on XC courses rarely requires the extreme compliance of enduro setups.
Trail riding is the broadest category. Use the calculator's MTB settings as your baseline. Hardpack trail: run towards the upper end of the range. Loose and rooty trail: run towards the lower end. Most trail riders settle 2–4 psi below their calculator starting point after a season of experimentation.
Enduro and gravity riding requires the lowest pressures — typically 4–6 psi below trail riding. The higher speeds, bigger features, and steeper terrain increase the importance of traction and rim strike resistance. Enduro riders frequently use tyre inserts, which allow them to drop another 3–5 psi without rim strike risk.
Tyre inserts (Cushcore, Rimpact, Nukeproof ARD) sit between the tyre and rim and provide a foam or polymer buffer against impacts. With inserts, you can safely run 3–5 psi lower than the standard recommendation. The insert adds 100–200 g per wheel — worth it for technical enduro, optional for trail riding, rarely justified for XC.