Tyre Pressure and Rolling Resistance: The Free Speed Most Cyclists Are Missing

For many cyclists, tyre pressure is a number they inflate to once and forget. They pump their tyres to whatever the sidewall says ("inflate to 80-120 psi"), ride on that pressure for weeks, and never consider whether it is optimal. This leaves meaningful performance on the table, and in some cases creates a less comfortable and less safe ride.

The science of rolling resistance and tyre pressure optimisation is more nuanced than the old rule of "harder is faster." Recent research, particularly from testing laboratories including Silca, Tour magazine, and Wheel Energy, has substantially changed the understanding of optimal tyre pressure.

Why Tyre Pressure Affects Speed

A tyre deforms as it rolls. This deformation requires energy, which comes from the rider. The energy lost in tyre deformation per unit of distance is called rolling resistance, measured as a coefficient (Crr) or as watts of power loss at a given speed.

Rolling resistance is one of three primary resistance forces a cyclist overcomes (alongside gravity and aerodynamic drag). On flat roads at typical road speeds, rolling resistance accounts for roughly 10 to 20% of total resistance. This is small but not trivial — reducing rolling resistance by 5 watts at 35 km/h is worth approximately 30 seconds per hour.

Here is the counterintuitive finding that has transformed tyre pressure thinking: beyond a certain pressure, increasing tyre pressure does not reduce rolling resistance. It often increases it.

The Road Losses Effect

At lower-than-optimal pressure, the tyre deforms excessively, creating significant energy loss through hysteretic deformation. This is the "flat tyre" effect everyone understands intuitively.

But at very high pressure on imperfect road surfaces (which is every road), the tyre becomes so stiff that it cannot absorb road vibration. Instead of the tyre deforming over surface irregularities, the entire bike (including the rider) is lifted and dropped over them. This vertical movement of the bike-rider system requires energy that comes from the rider's forward momentum. This is the "road losses" or "bump losses" effect.

The optimal tyre pressure for any given situation is the pressure at which tyre deformation losses and road losses are balanced at a minimum. On perfectly smooth surfaces, the balance point is at higher pressures. On rough, undulating, or chip-and-tar road surfaces, the optimal pressure is significantly lower than most cyclists run.

For typical UK road surfaces, this balance often occurs at pressures 15 to 30% lower than conventional wisdom has suggested.

Tyre Width Changes the Calculation

Wider tyres change at what pressure the balance point occurs. A wider tyre at lower pressure has more volume, allowing the tyre to act as a larger air spring that absorbs road bumps without excessive vertical movement. To get the same bounce absorption from a narrow tyre, you need lower pressure (which increases deformation losses) or you accept more road losses at high pressure.

This explains why road cycling has steadily shifted from 23mm tyres at very high pressures (110 to 130 psi) toward 25mm, 28mm, and 32mm tyres at significantly lower pressures. Modern testing consistently finds that 28mm tyres at 70 to 80 psi roll as fast or faster than 25mm tyres at 100 to 110 psi on the same road surfaces, with improved cornering stability and puncture resistance as a bonus.

For most UK roads, a 28mm or 30mm tyre is optimal for the combination of rolling resistance, comfort, and handling. Only on smooth indoor tracks or velodromes do narrower tyres at extreme pressures show meaningful advantages.

Calculating Your Optimal Pressure

Several tools and calculators help estimate optimal tyre pressure based on rider weight, tyre width, and riding surface. The most accessible is the Silca tyre pressure calculator, which accounts for all relevant variables.

Key inputs:

Rider plus bike weight: Heavier riders need more pressure to support the load without excessive deformation. A 65kg rider and a 90kg rider with identical bikes and tyres should run different pressures.

Tyre width: Wider tyres require lower pressure to achieve the optimal deformation amount. A 28mm tyre at 70 psi has more internal volume than a 23mm tyre at 70 psi and therefore deforms less.

Front vs rear distribution: Most bikes carry approximately 40 to 45% of weight on the front wheel and 55 to 60% on the rear. The rear tyre needs more pressure than the front to support proportionally more load. Many cyclists run equal pressures front and rear, which typically means the front is overinflated and the rear is correctly inflated, or the rear is correct and the front is too high.

Road surface: Rough roads lower the optimal pressure; smooth roads raise it. For sportive riding on mixed surfaces, use the rough surface estimate.

A Practical Framework

For a 75kg rider on typical UK road surfaces with 28mm tyres: - Front: approximately 65 to 70 psi (4.5 to 4.8 bar) - Rear: approximately 70 to 75 psi (4.8 to 5.2 bar)

For the same rider on 25mm tyres: - Front: approximately 80 to 85 psi - Rear: approximately 85 to 90 psi

These ranges are starting points. You may find 5 psi lower or higher suits your preference and your roads. What you should not do is default to maximum sidewall pressure, which is typically 10 to 25 psi higher than optimal for most road cyclists.

Tubeless Tyres

Tubeless tyres (tyres that seal against a tubeless-ready rim without an inner tube, using sealant) can be run at even lower pressures than clinchers without pinch flat risk, because there is no inner tube to pinch. This allows accessing the lower end of the optimal pressure range more safely.

Rolling resistance of tubeless tyres is also typically 2 to 5 watts lower than equivalent clinchers due to the absence of inner tube flex losses. For riders who can access tubeless-compatible wheels, the combination of tubeless tyres and optimised lower pressure represents meaningful free speed.

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