There comes a moment in every cyclist's hill-climbing life when they think: sod this for a game of soldiers; I'll get off and push. As soon as that little gremlin of doubt pops into your head, you're done for. It is a matter of pride not to dismount once you start a climb - a test of mental resilience rather than fitness - but everyone has days of weakness.
So I was wondering: when is it more efficient, in terms of energy expended, to get off and push your bike than to struggle onwards and upwards in the saddle?
Perhaps it's best not to know. When you're toiling up a mountain or that steep hill on the way home from work you sometimes have to shut off the logical part of your brain and close yourself down like a blinkered old nag to stagger to the top. Especially if there's another cyclist on your tail.
But forget the competitive stuff; let's consider an everyday example. A typical steep hill for a commuting cyclist probably has a gradient of 15%. Faced with this, he'll select a low gear and toddle on at the slowest speed at which he can balance. Tough, but doable.
Efficiency comparison is not an easy calculation since there are so many variables. However, drawing from a variety of research over the past 40 years, David Wilson, author of Bicycling Science, has made a good stab at it. His conclusion is blindingly bike-nerdy but I love it.
Advertisement
His studies take into account the oxygen consumption of pedestrians and pedallers, their metabolic gross efficiency (energy required to move the bike and/or body), air resistance and gearing. After considering all the data, Wilson calculated that it would be 18% more efficient for a cyclist to ride up a 15% gradient at 1.5mph than it would be for a walker. At anything steeper than 20%, it would be better to dismount.
All the boy racers will frown at this. They'll probably say that if he's moving at only 1.5mph at 15%, then the wuss would be at a standstill and fall off at 20%. But Wilson's assumption here is of an ordinary cyclist who doesn't want to expend more than about 75 watts of power.
In the real world it is not always efficiency that springs to mind; it's the perception of effort. The normally dressed cyclist in this experiment will have a body temperature rise of about 0.5C on the hill, which means he'll feel a bit hot and bothered even at his creeping pace. That is the gremlin that will probably make him dismount on a commute.
Riding round the Kent hills, I've found one with an impossibly steep section: you have to lean so far forward, the rear wheel doesn't have any weight and therefore has no traction. On a wet day it cannot be done. A more devilish efficiency question might be: how steep does a hill have to be to stop you cycling up it, however much power you apply?
A few years ago I thought I'd found one in France. (I hadn't - I'd just run out of puff.) I wobbled to a halt, then keeled over sideways, still clipped into my pedals, like a fallen tree. And, of course, I was too embarrassed to measure the gradient. So, back to you, David Wilson.