Run your front tyre 2–4 psi lower than your rear. On a typical road bike, 40% of system weight is on the front wheel and 60% on the rear. All three major calculators reflect this: SRAM uses a 42/58 front/rear load split, Silca 40/60, Pirelli 41/59. The front needs less pressure because it carries less weight.
Weight distribution and why it drives pressure
Tyre pressure is fundamentally about managing the contact patch under load. Inflate too high and the contact patch shrinks, reducing grip and transmitting road vibration directly to the rider. Too low and the contact patch grows too large, rolling resistance rises, and the tyre starts to squirm under lateral load.
The optimal contact patch size scales with the load on that wheel. Since road bikes put roughly 40% of system weight on the front wheel and 60% on the rear, the rear tyre needs to support more weight and therefore runs at higher pressure. The front runs lower — and this isn't just a preference, it's the physically correct setup for minimising rolling resistance and maximising grip simultaneously.
The actual split varies by bike type. An aggressive road position moves weight forward slightly (towards 43/57). A relaxed endurance position or a loaded touring bike pushes it back further (38/62). Calculators use fixed standard splits — they can't know your exact position — so treat the output as a calibrated starting point rather than a precise measurement.
How the three calculators implement front/rear splits
SRAM's AXS calculator uses a 42/58 front/rear load split. This is slightly more weight-forward than Silca's 40/60 split, which means SRAM's front pressure recommendation is marginally higher relative to the rear. In absolute terms, for a 85 kg system on 32 mm road tyres, SRAM recommends approximately 68 psi front / 77 psi rear. Silca recommends 65 psi front / 79 psi rear — a slightly lower front and higher rear.
Pirelli uses 41/59, landing between the two. Their rear pressure tends to be slightly lower than Silca's because their K constant is calibrated differently.
In practice, the difference in the front/rear gap between calculators is 1–2 psi. All three agree on the direction: front lower than rear by 3–8 psi depending on weight and width. What changes is the magnitude — larger riders on narrow tyres see bigger front/rear gaps; lighter riders on wide gravel tyres see smaller gaps.
When to break the rule
The 2–4 psi rule covers 90% of riding. The remaining 10% involves setups that shift the actual weight distribution away from the standard assumption:
On a heavily loaded bikepacking setup with panniers, the rear carries proportionally more weight and should run higher than the standard formula suggests. If you're carrying 10 kg of rear load, add 4–6 psi to the calculator's rear recommendation.
On modern enduro MTB bikes with aggressive slack geometry, the rider weight can shift to 45/55 or even 50/50 in some configurations. Running equal pressure front and rear is reasonable on these setups — the geometry puts the rider further back relative to road bikes.
On technical terrain where front grip is paramount — loose gravel corners, wet descents, rooty singletrack — run the front 5–6 psi lower than standard. The penalty in rolling resistance is worth the traction gain when the consequences of front wheel wash are severe.
One setup not to break the rule for: smooth road cycling. Some riders intuitively feel that running equal pressure front and rear gives a more "balanced" feel. It doesn't — it just means the front is overinflated and losing grip and compliance for no efficiency gain.