Max speed on bike

Equipment
1

I’ve been thinking about this for a while whilst looking over strava segments; most of the flat KOMs have been taken at 52-55km/h. Regardless it seems if there is a group, or solo or slight downhill the speed is invariably the same.

Is there a max velocity that cyclists hit beyond which the power is too much? How hard is it to get to 60km/h on a flat segment assuming we’re not all out sprinting?

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Depends mostly on aerodynamics at higher speed. The current world record when drafting behind a vehicle is nearly 184 mph, set by Denise Mueller-Koronek in 2018.

3

The coveted flat KOMs down here in Socal are done on TT bikes on a good tailwind day.

Sustainable power in an aero position is often the limiter.

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4

Yup, aerodynamics are the major limiter and it only gets worse as speed increases. So, rider position and clothing will have the greatest impact, with wheels, helmet and bike helping with decreasing influence.

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5

Wind resistance is exponential. Going from 50kph to 60kph requires a lot more power. Out of interest I plugged the numbers into this calculator - Bike Calculator - and it reckons in the drops position a 70kg rider needs ~550W for 50kph and ~920W for 60kph. That’s a huge difference - lots of people can hold 500W for a minute or more, most would struggle to hold 900W for much more than maybe 20 seconds and they’d also struggle to hold that kind of number while also staying as aero as possible. That’s an estimate of course but it gives you an idea of the kind of step up in power (and/or aero) to jump from 50 to 60.

So yeah, 60kph on a flat road is pretty much an “all out sprinting” speed.

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6

As a rider rides through the air, they push the air forwards. The simple mechanics of this are:

  • mass of air being accelerated up to speed v by rider size A, per second: A * v * rho
  • energy of air of mass m moving at v: 0.5 * m * v**2

hence, energy per second being created by the rider is 0.5 * A * rho * v**3

plugging some numbers through, say A is 0.3 m**2, rho is 1kg/m**3, v is 17 m/s

you have 0.5 * 0.3 * 17**3, which is 740W.

This is neglecting rolling resistance, and A is actually CdA. This is why trains are so much better for the environment than cars.