Your ideal tire pressure depends on your weight, your bike's weight, tire width, and the road surface — not a single number printed on the sidewall. This calculator estimates front and rear pressure from your own numbers, using a published formula you can check for yourself.
45% front, 55% rear, and the psi gap that follows
What comes back is the pressure that suits your weight, your bike, your tire width and your riding surface — not a number copied off the sidewall, which lists only that tire’s safe maximum rather than the pressure your setup actually wants.
The front and rear numbers are separate on purpose — most bikes carry more weight on the rear wheel, so it typically needs a few psi more than the front to hit the same target tire drop. Treat both as a starting point: air up to the suggested pressure, ride your usual roads, and adjust a few psi at a time based on feel. If either number shows the built-in floor, or a wide-tire warning appears, lean more on your tire’s own printed range than on this estimate.
With a rider in a forward-leaning position the rear wheel often carries 55–60% of the load, which is why it needs those extra psi to reach the same drop. Running identical front and rear pressure usually means the front is slightly over-inflated relative to the load it is actually carrying.
153.6 × load ÷ width^1.5785, and the 15% drop it targets
Nothing here is a black box. The base pressure comes from Frank Berto’s published research — 153.6 × wheel load (lb) ÷ tire width (mm)^1.5785 − 7.1685 — targeting roughly a 15% drop in tire height under your weight, the balance point most riders find comfortable and efficient. That figure is then adjusted for tire type and terrain.
The 15% benchmark is what Berto settled on after measuring how much dozens of tires compress under load: at about a 15% drop in tire height (roughly 20% measured from rim to ground), most tires balance rolling resistance, comfort and grip reasonably well. It is a widely cited starting point, not a law of physics.
What the estimate holds fixed while you change one number:
- Total riding weight is rider weight (with gear) plus bike weight, split between front and rear wheels by the percentage you enter — about 45% front / 55% rear is typical for a drop-bar road position.
- The base pressure targets roughly a 15% tire drop under load, the benchmark from Frank Berto’s original research.
- Tubeless setups are assumed to run about 10% lower than tubed for the same feel, since there’s no tube friction and no pinch-flat risk at the same pressure.
- Rougher terrain reduces the target pressure, since lower pressure generally improves comfort and control once a road gets bumpy, at a small cost in smooth-road rolling resistance.
- A 18 psi floor applies regardless of the raw formula output — pressures below that risk rim strikes on almost any setup.
160 lb on 28mm tubeless comes out at 51.1 front, 63.9 rear
A 160 lb rider on an 18 lb road bike, 45% of the weight on the front wheel, running 28mm tubeless tires on smooth pavement. Total system weight is 178 lb, split into an 80.1 lb front load and 97.9 lb rear load. The formula suggests 51.1 psi front and 63.9 psi rear — noticeably lower than older tubed-tire guidance for the same tire, which reflects the roughly 10% reduction this calculator applies for tubeless setups.
That discount is not cosmetic. The same tire with an inner tube wants more air, because the tube adds friction that drags on rolling resistance and brings pinch-flat risk — the tube caught between tire and rim on a hard hit. With neither of those to worry about, a tubeless setup can run lower for the same feel.
Rougher surface, lower psi — smooth pavement is the exception
Rougher surfaces generally benefit from lower pressure: it lets the tire absorb bumps instead of transmitting them into the bike and rider, which improves comfort, control, and — on real-world rough roads — can even lower overall rolling resistance despite the tire itself flexing more. Very smooth pavement is the one situation where higher pressure has the fewest downsides.
Gravel sits inside this model rather than at its edge. Enter your gravel tire’s actual width (commonly 35–45mm) and choose “Gravel / light off-road”: that range is comfortably the range the formula was built from, unlike full mountain-bike widths.
The 18 psi floor sits between two ways of getting it wrong
Too high, and the tire cannot absorb small bumps, so it bounces and transmits more vibration into the bike — usually a harsher, less controlled ride, and on rough surfaces, not necessarily faster. Too low, and the tire deflects too much, increasing rolling resistance, risking a pinch flat or rim strike on a hard hit, and making the bike feel vague in corners.
The floor exists specifically to stop the second failure being recommended: whatever the raw formula returns, the output never drops under 18 psi. A result sitting exactly on it is the tool saying it has run out of range — check your tire’s own printed minimum before you ride that number.
Wide MTB tires, and why SILCA answers with a different number
For mountain-bike widths this is not precise: the underlying research measured tires roughly 20–45mm wide, and the formula extrapolates poorly beyond that, sometimes suggesting unrealistically low numbers before the safety floor catches them. Treat the result as a rough starting point for wide tires, and lean more heavily on your tire and rim manufacturer’s guidance.
Commercial calculators such as SILCA’s give different figures because they are built differently, not because one is more “correct”. This page uses a published, reproducible formula from Berto’s tire-drop research. SILCA’s is based on their own proprietary field testing — finding the pressure “breakpoint” where rolling resistance and surface impedance cross over, across many tire and terrain combinations they have measured themselves. Both are reasonable starting points; neither replaces testing on your own roads.
The limitations worth reading before you trust a number from this page:
- Built from road/gravel-width tire data (roughly 20–45mm); it extrapolates poorly to wide mountain-bike tires, where it becomes a rough starting point only.
- Frank Berto’s 15%-drop benchmark came from tire manufacturers’ own recommendations in the 1990s, not independent lab testing, and modern supple, high-thread-count tire casings can behave differently at the same pressure.
- Does not account for rider skill, riding style, or personal preference — many riders end up a few psi off this estimate once they’ve experimented on their own roads.
- Does not replace your tire and rim manufacturer’s stated minimum and maximum pressure, which always takes priority.
- This is a different, and simpler, model than commercial calculators (like SILCA’s) that are built from proprietary field-testing rather than a published formula — see above for how the two differ.