What determines descent speed?

Terminal descent speed is determined by the balance between gravity pulling you downhill and air resistance plus rolling resistance slowing you. Heavier riders descend faster due to higher gravitational force relative to drag.

Why do heavier riders descend faster?

Weight increases gravitational force linearly but drag stays the same (it depends on size, not weight). A 90 kg rider will reach a higher terminal speed than a 60 kg rider with the same aerodynamic profile.

How does braking affect descent?

The braking settings are an indicative speed-management illustration rather than a precise physical brake model. Light braking reduces the freewheel terminal speed by roughly 13%, moderate by about 26% and heavy by around 41%. The effect on speed is smaller than the force scaling because speed varies with the square root of the net driving force, so trimming the force has a sub-linear effect on the resulting speed.

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Descent Speed Calculator — Estimate Downhill Speed

Estimate safe descent speed based on gradient and conditions.

Descent Gradient

Average descent slope as a percentage (rise ÷ run × 100). A typical fast road descent is 4–8%; Alpine passes reach 8–12%.

Total Weight

Combined rider + bike + kit mass. Heavier systems reach higher terminal speeds for the same drag area.

CdA

Drag area (m²): ~0.40 upright/hoods, ~0.30 on the drops, ~0.25 in a full descender's tuck. Lower CdA means higher descent speed.

Crr

Rolling resistance coefficient: ~0.004 fast slick road tyres, ~0.006 typical clinchers, ~0.010 wet or rough surfaces.

BrakingIndicative speed management. Relative to a free freewheel, light braking trims roughly 13% off terminal speed, moderate about 26% and heavy around 41%.

How We Calculate This

Terminal Descent Speed

At terminal velocity (steady freewheel speed), the slope component of gravity equals aerodynamic drag plus rolling resistance. The gradient percentage is rise/run × 100 = tan(θ), so θ = atan(gradient ÷ 100):

Net driving force = m × g × sin(θ) − Crr × m × g × cos(θ)
Terminal speed = √(2 × Net force ÷ (air density × CdA))

Heavier riders reach higher terminal speeds because the gravity term scales with mass while the dominant aerodynamic drag term does not. The braking option scales the net driving force to illustrate speed management — it is an indicative scenario, not a precise brake-force model.

Frequently Asked Questions

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Last updated: February 2026

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