Tyre pressure is one of the few race-day variables you control in minutes — yet many athletes inflate to a remembered number or the sidewall maximum. Over hours on the bike, PSI changes rolling resistance, vibration 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 in T2.
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. 28 mm often rolls faster on chip-seal than 23 mm rock-hard.
Smooth ↑ · Mixed −5% · Wet −10% vs reference.
Clincher floor vs tubeless (+~7% modifier) vs tubular in WattX math.
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)
Change width to 25 mm and pressure rises; 32 mm lowers it. Always confirm in the calculator — illustrations only.
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 Explained 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 long Build Blocks from Race Planning Explained, verify equipment details before you lean on fitness alone. The Race Week Explained walkthrough covers checklist, maintenance, nutrition, and when to set PSI on site.