What CdA value should I use?

Typical CdA values: road bike on hoods 0.35-0.40, road bike on drops 0.30-0.35, TT bike with aero position 0.22-0.28. Professional TT riders can achieve 0.20-0.22.

Does this account for hills?

This calculator assumes a flat course. For hilly TT courses, actual times will be slower as power spent climbing is not recovered on descents due to air resistance increasing with speed.

What is a good 10-mile TT time?

For a 10-mile (16.1 km) TT: under 25 minutes is good club level, under 22 minutes is competitive, under 20 minutes is elite. Course and conditions make a big difference.

How does this calculator work?

It uses Newton–Raphson iteration to solve the power equation: WheelPower = 0.5 × CdA × rho × v³ + Crr × m × g × v, finding the speed that matches your power output. Your entered power is treated as crank power and reduced by a 2.4% drivetrain loss (drivetrain efficiency 0.976, per Martin et al. 1998) to give power at the wheel.

bikecalcs.uk

Time Trial Calculator — Estimate TT Finish Time

Estimate your time trial finish time from power, CdA and course distance.

Average Power

Your average power at the cranks (from a power meter) for the effort

Rider Weight

Your body weight including kit, shoes and helmet

Bike Weight

TT bike with bottles and accessories, typically 7–9 kg

Distance

10-mile TT = 16.1 km, 25-mile = 40.2 km

CdA (Drag Area)Aerodynamic drag area (CdA) in m² — lower is faster

How We Calculate This

Time Trial Physics

On a flat course, your power must overcome two main forces:

Aerodynamic drag: F_drag = 0.5 * CdA * rho * v^2
Rolling resistance: F_roll = Crr * m * g

Power at the wheel: P_wheel = (F_drag + F_roll) × v = 0.5 × CdA × rho × v³ + Crr × m × g × v

Your entered power is measured at the cranks, so we first apply a 2.4% drivetrain loss (efficiency 0.976, per Martin et al. 1998) to get power at the wheel. The calculator then solves this cubic equation iteratively using the Newton–Raphson method to find the speed that matches your power. Time is then simply distance ÷ speed.

Default values: air density (rho) = 1.225 kg/m³ at sea level, rolling resistance (Crr) = 0.004 for good road tyres on asphalt.

Frequently Asked Questions

Related Calculators

Speed Calculator

Calculate your cycling speed from distance and time.

Distance Calculator

Work out distance covered from speed and time.

GPS Distance Calculator

Estimate true distance from GPS coordinates with elevation correction.

Split Calculator

Calculate split times for even-paced riding.

Wheel Speed Calculator

Calculate wheel RPM and speed from tyre size and cadence.

Was this calculator helpful?

Last updated: June 2026

All calculations are estimates. Always verify results and consult a professional bike fitter where appropriate.