Many athletes pump to a number they remember, or to the maximum on the sidewall. Over hours on the bike, pressure affects rolling resistance, how much vibration you carry into the run, and puncture risk.
Optimal pressure depends on system weight, tyre width, surface, and tyre construction — not a single chart for all riders. WattX calculates front and rear targets from your profile and setup; this guide explains why the number matters before you dial it in.
Why it matters
Why Pressure Matters
Too hard on real roads adds vibration loss; too soft adds deformation and pinch risk.
Harsh vibration over 90–180 km costs you on the run.
Slightly lower PSI in wet conditions enlarges the contact patch.
Variables
Variables That Move the Number
Rider + kit + bike. “100 PSI” without weight is meaningless.
Wider = less PSI. On rough roads, a 28 mm tyre often rolls faster than a rock-hard 23 mm.
Smooth roads: the reference pressure. Mixed: about 5% lower. Wet: about 10% lower.
Clincher, tubeless or tubular: each needs a slightly different pressure, and the calculator adjusts for it.
Rear carries ~55–60% load. Front typically rear − 3 PSI.
Calculator
Use the Calculator, Not a Static Table
Static charts (weight × width matrices) are useful for intuition but go stale the moment your weight, bike, or course changes.
The Tyre Pressure Calculator uses your system weight, tyre width, surface, and setup — reference ~70 PSI rear at 85 kg on 28 mm tubeless smooth road, then adjusts for weight, width, mixed (−5%) or wet (−10%) roads, and tyre type. Front = rear − 3 PSI. Pull weight from your profile and bike garage when they are set.
Reference pressures (tubeless, smooth, 28 mm)
Narrower tyres need more pressure, wider ones less. These are examples only; use the calculator for your numbers.
Workflow
Practical Workflow
Weigh rider + kit + bike (WattX pulls from profile when set).
Measure tyre width honestly — marked size ≠ mounted width.
Select surface and tyre type for race day in the calculator.
Read front and rear PSI; re-check race morning on-site with the same pump.
See race week for where PSI fits in final prep.
Race week
Link to Race Week
Pressure sits beside Race Pacing Targets in final prep — small error, measurable cost over hours.
After months of training, don’t let a small equipment detail cost you on race day. The race week walkthrough covers checklist, maintenance, nutrition, and when to set PSI on site.