Opinion: Why Climbing Efficiency Matters More Than You Think

I occasionally hear mountain bikers say that they don't care about climbing efficiency at all. "I'll get there when I get there" is something I often hear.

But do you ever wonder why pro mountain bikers often train on lightweight, efficient road bikes? If the goal is to get stronger and fitter, wouldn't a less efficient bike be just as good, if not better?

Victorian economist William Stanley Jevons might have an insight into this. In 1865, he noticed that whenever steam engines got more efficient, people used more coal, not less. This phenomenon has become known as the Jevons paradox, which occurs when improved efficiency leads to lower costs, and lower costs lead to more energy use.

A more recent example is the increase in vehicle fuel efficiency has probably contributed to an even bigger increase in driving in many countries, as it makes going by car more cost-competitive when compared to public transport, cycling, or even living in a walkable neighbourhood.


If this seems totally counter-intuitive, think of it like Tim Hortons offering a two-for-one deal on donuts, hoping you'll spend more money, not less.


What's this got to do with cycling?

You often hear bike reviewers say that efficient bikes seem to push you to pedal harder, while inefficient ones encourage you to take it easy. I've experienced this myself - I used to ride all kinds of test bikes home from the office on the same hilly route, and whenever I was commuting on a road bike or XC bike, I'd usually try harder and break more of a sweat than on an enduro bike.

This makes sense in the context of the Jevons paradox because, with a more efficient bike, you get more bang for your buck in the form of extra speed for every extra watt you put in. Your effort is more rewarded.

This means that with a more efficient bike, you're not just going faster and further for every unit of power you can squeeze out of your legs; you might put down more power too, and end up going even further or faster than you'd expect from the efficiency gains alone.

You might even get fitter as a result, or squeeze an extra lap into your lunch ride.


What makes a bike efficient?

By efficiency, I mean how much distance or height gain you can achieve for a given amount of energy input at the crank. There are several factors that affect this.

The most obvious one is weight. But as we discussed in a previous article, saving a kilogram (2.2 lb) from your bike will only make you go about 0.2% to 1% faster, depending on how steep the hill is. Of course, there is scope to save more than one kilo when comparing enduro bikes to XC bikes, or if you include the rider and riding kit, but when comparing similar bikes, it's probably not the biggest factor.

In another article, we found the difference in climbing speed between a Nukeproof Reactor (a 130 mm travel trail bike) and a Nukeproof Giga (a 170 mm travel "parkduro" bike *sighs*) was less than 1% when using the same tires. Yet in the same test, we found that swapping from trail tires to Enduro tires (thicker casing, stickier rubber, more aggressive tread) made the bike go over 4% slower for the same power.

An idler pulley costs at least 2% in drivetrain efficiency, and even the choice of chain lube can affect efficiency by more than 1%.

Suspension efficiency (pedal bob), geometry, chain line and more can play a role too. The overall result, according to previous efficiency tests, is that some bikes can be as much as 10% less efficient than others in the same category, meaning they went 10% slower for the same power.


What about e-bikes?

If getting more reward for your effort encourages you to pedal harder, does that mean an ebike is the ultimate training tool? Not necessarily. The Jevons paradox is not a law of nature; it's only observed occasionally.

For example, LED lightbulbs are at least four times more efficient than incandescent bulbs. This may lead to more widespread use of lighting, but not four times more, so LED bulbs are thought to have significantly reduced electricity use around the world.

So how does it work out with e-bikes? One study had 33 mountain bikers ride a regular bike and an electric mountain bike for one lap each and compared the effort with heart rate monitors. The average heart rate was similar on both bikes, suggesting riders weren't taking it easier on the e-MTB (although they were riding for less time).

With some motors, it is possible to soft-pedal and let the electrons do most of the work. On the other hand, several e-bike converts insist they ride more often than they otherwise would, tackling steeper climbs and more trails. So, it probably depends on the rider.

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Reviews and Tech Op Ed Seb Stott