The weight myth: Why we ignore the real energy guzzlers

​Shedding a kilo on your bike often costs a four-figure sum – and makes very little difference. The laws of physics clearly show that the real performance-killers lie elsewhere.

​Conclusion

Fine-tuning weight down to the gram is something for techies and perfectionists. After all, the quest for the lightest bike is an expensive hobby that often comes to nothing in practical terms. Road cyclists gain an advantage through aerodynamics and tight-fitting clothing, gravel cyclists through the perfect tubeless set-up with boldly reduced tyre pressure on gravel, and mountain bikers simply get the most out of their bikes through perfectly maintained, clean drivetrain components and maximum tyre grip on steep climbs. So, if you’re smart, you’ll start by cutting back on the real power guzzlers – and only tackle weight right at the very end.

​In the world of cycling, the mantra is: lighter is better. Manufacturers are outdoing one another with thin-walled carbon-fibre frames, carbon rear triangles, titanium bolts and hollow axles in an effort to reduce the overall weight. But anyone who analyses the raw physical forces at work on a bike will quickly realise that the industry is often selling us expensive plasters for the wrong wounds. Depending on whether we’re riding a road bike, a gravel bike or a mountain bike, the laws of physics shift dramatically.

The biker’s four opponents

To keep a bicycle moving, the body has to overcome four main forms of resistance: the resistance of the gradient (F-st), aerodynamic drag (F-w), rolling resistance (F-r) and mechanical friction losses (F-foreign) in the drive system.

The total power P (watts) is the sum of the individual power components, i.e. force multiplied by the relevant speed in each case. Weight is a factor solely in the climbing resistance and, to a minimal extent, in the rolling resistance. As soon as the route levels out, the weight advantage is almost entirely lost – but on the climb, it really comes into its own.

Road bike: The merciless tyranny of the wind

Average speeds on a road bike are often high. Amateur cyclists manage an average of around 30 km/h, whilst very fit road cyclists achieve speeds well above that. Because air resistance increases in proportion to the square of the speed, aerodynamics is the overriding factor here.

• The weight: Even on long Alpine passes (e.g. 10 km long, 7 per cent gradient at a constant 250 watts), an exorbitantly expensive weight reduction of 1 kilogram yields a time saving of only around 25 seconds (approx. 2.5 watts). In the Tour de France, that’s obviously a significant amount, but in amateur cycling it’s probably negligible. And on flat terrain, the effect is barely measurable.
• The greatest lever: Aerodynamics. Yet the greatest potential for savings lies not in the frame, wheels or handlebars, but in the rider themselves. They account for 80 per cent of the drag. Tight-fitting road cycling kit, compared with flapping wind jackets, easily saves 25 watts at 35 km/h. An aerodynamically efficient riding position also pays off massively.
• Ergonomics factor: A streamlined riding position is therefore important, but: anyone who sits on their bike in a position that is aerodynamically low but biomechanically completely restricted will immediately lose 5 to 10 per cent of their performance due to poor muscle power transfer.

Gravel bikes & MTBs: The rolling resistance paradox

When it comes to rolling resistance, many cyclists still harbour a serious misconception from the old days of road cycling: “The harder the tyre is pumped up, the faster it rolls.” On perfectly smooth tarmac, this is true. However, as soon as we venture onto rough surfaces – particularly gravel, forest tracks or trails – this logic is turned on its head. Here, the principle is: lower tyre pressure means greater speed.

The physical secret: impedance beats walking effort

A tyre on uneven ground loses energy in two ways:

• Walk-work (hysteresis): The tyre deforms as it rolls. This costs energy. A firm tyre deforms less.
• Impedance (micro-suspension): A tyre inflated to the absolute limit cannot absorb bumps (pebbles, roots, coarse gravel). The entire bike, including the rider, is lifted slightly off the ground with every small stone. From a physical point of view, this constant vertical lifting of the system’s weight is a form of continuous lifting work – and that costs a huge amount of forward momentum. A softer tyre, on the other hand, moulds itself around the obstacle. The bike rolls smoothly straight ahead, whilst only the tyre ‘absorbs’ the unevenness. Anyone who pumps up their gravel bike to 4 bar for a gravel ride, instead of the material-friendly 2.5 bar (for tubeless tyres), suddenly loses 15 to 25 watts on rough terrain due to the impedance effect. Although the rock-hard ride feels subjectively fast because of the vibrations in the handlebars, the watch and the power meter show the opposite: you’re riding into an invisible wall of vibrations.

Mountain biking: A dirty drivetrain ruins your performance

With mountain biking, the priorities shift completely. On technical trails in the woods, the average cycling speed (without a motor) is rarely more than 12 to 15 km/h. On flat terrain and on technical trails, air resistance is therefore absolutely negligible at low speeds. However, mountain bikers often wear loose-fitting, sturdy baggy trousers and loose-fitting jerseys. This comes back to haunt them as soon as they pick up speed on forest tracks or a headwind blows straight into their faces.

• The Flattershirt calculation example: A mountain biker is cycling along a long, flat stretch of gravel road at 25 km/h against a light headwind (effective wind speed 30 km/h). Switching from loose-fitting baggy trousers and a loose-fitting jersey to close-fitting cross-country kit saves energy due to the lower aerodynamic drag (Cw (value) at this pace is around 15 to 22 watts. Anyone who lets their loose-fitting clothes flap in the wind is, from an energy perspective, effectively riding with a brake constantly applied.

Weight vs. Steepness

MTB routes, particularly in the Alps, often have only two modes: steep uphill or steep downhill. On off-road gradients of 12 to 20 per cent, the bike’s overall weight becomes your main adversary. This is where a lightweight bike really makes a difference, because the effort required to pedal takes centre stage. However, when it comes to MTB, a super-light carbon frame is of little use if the tyres have to be heavy to prevent punctures. The weight of the rotating parts (wheels/tyres) feels twice as heavy when accelerating off-road. Thanks to modern tubeless systems, however, you can get the most out of this: less weight due to the absence of an inner tube, combined with low tyre pressure for minimal rolling resistance off-road.

The Crunch Drive: MTB maintenance beats lightweight construction

However, the biggest drain on power when mountain biking is mechanical in nature. The drivetrain suffers greatly from mud, dust and puddles.

• A clean, waxed MTB drivetrain loses only around 1–2 per cent of its power (approx. 3–5 watts at 250 watts). Clean chains lubricated conventionally with oil lose between 1.5 and 2.5 per cent.
• A completely grubby, squeaky chain dramatically increases friction on the chain, cassette and the tiny derailleur pulleys. According to studies, the power loss amounts to 10–20 watts and, in extreme cases, can even rise to 25–30 watts.

A direct comparison of the bicycle categories