Cycling on hilly roads, what is the best option to save energy: go as fast as possible downhill to gain momentum for the next climb, or stop pedalling to have a rest and regain some strength?
Hillary Shaw
Newport, Shropshire, UK
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Without air or friction, and if every hill were the same height, a cyclist would need no energy input – downhill speed would just take them up the next hill. Rollercoasters work a bit like this.
But in reality there is friction and air, and the faster you travel, the more energy goes into overcoming these things. So, you should freewheel down and save your energy for the next hill. As you slow down, pedal to boost your uphill speed and delay slowing so much that you must dismount.
Steve Willey
London, UK
Freewheel. Save your energy.
Having ridden a bicycle from Bogotá in Colombia to Lima in Peru, among other moderately hilly excursions, I am intimately familiar with this conundrum.
Unless the resultant climb is short, there is no point in wasting energy by pedalling on the descent, as gravity on the climb will get you very soon and you usually need all the energy you can muster. Additionally, you rarely get just a hill, singular, on your journey. There is always another one waiting just over that brow unless you are cycling somewhere flat where the wind will probably get you anyway.
Cyclists sometimes pedal downhill because the psychological benefit of making progress is worth the effort
Having said all that, I would rather cycle uphill all day than cycle into a headwind all day.
Chris Daniel
Glan Conwy, UK
When going downhill, it is tempting to pedal as fast as possible to maximise speed and therefore kinetic energy, which can be translated into potential energy in the subsequent ascent. This may not be the best strategy.
Cyclists are aware that the greatest source of drag is aerodynamic resistance. The power output required to overcome it rises with the cube of velocity, so a lot of additional effort is needed for only a small gain in speed. For example, from 22 kilometres per hour to 25 km/h is a 14 per cent increase in speed, but it requires 47 per cent more power.
At this speed, wind resistance amounts to 70 per cent of the total drag – the rest rolling resistance between the tyres and the road, mechanical frictional forces in the drive train and axles, and gravitational resistance. However, when going at a more sedate pace up a hill, the gravitational force will predominate.
Fortunately, most bikes have a wide range of gears. It is sensible to take advantage of gravitational acceleration when going downhill by pedalling in high gear at an increased speed, but with no more than your normal power, so that you aren’t additionally battling increasing aerodynamic resistance, tiring yourself out before the ascent ahead of you. The acquired kinetic energy will take you uphill until your speed has decayed to a point at which you can change to a lower gear and continue pedalling at a hopefully manageable power output to the top.
Ian Cairns
Seaford, East Sussex, UK
The best option to save energy is to stop pedalling. The additional kinetic energy gained by pedalling downhill is less than the total energy expended, as energy is increasingly lost in overcoming air resistance, which is proportional to speed. Still, cyclists often pedal downhill because the psychological benefit of making progress on the next hill is often worth the extra effort. Also, if the previous uphill has been a long slog, it can feel good to “warm down” the legs by pedalling downhill – and, of course, going fast can be fun in the right situation!
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