In This Series
- How to Cycle Faster According to New Book Cycling Science
- Get Fitter Cycling
Photography: Glen Burrows. Model: Ben Bradley@WModels
Understanding the key factors behind moving efficiently on two wheels can help you get fitter and go faster. You’ll find Glaskin’s advice on how to cycle faster below, and on the next page why working out on two wheels can improve heart health and help you live longer.
Understanding external forces and basic aerodynamics can give you a speed injection. There are four external forces that every cyclist must work with or against. These are gravity, air resistance, rolling resistance and friction – and there’s a fifth effect, referred to as inertia. None of them can be entirely vanquished (and it would not necessarily be desirable to do so). However, it is wise to understand what you’re dealing with for each of these so that you can minimise the negative consequences and harness the positive.
As you may remember from school science lessons, it’s the force that gives weight to matter. The Earth pulls everything to itself with a gravitational acceleration of about 9.8m/sec2. In fact, gravity is obviously what makes cycling possible – by pressing the bike to the ground – while it also makes riding uphill harder. Descending is made easier by the pull of gravity, but you never get back all the energy you put into climbing the same hill.
2. Air Resistance
This generally works against the cyclist. The planet’s gravity is strong enough to hold a blanket of air 100km thick to the Earth’s surface. Although none of us could breathe without it, cyclists must push it aside continually to make progress.
This same force can be helpful, too, if you’ve got a fair tailwind. A cubic metre of dry air at 20°C at sea level has a mass of about 1.2 kg. When the cyclist and the atmosphere meet head on, some of a rider’s energy is lost to pushing this air out of the way. If the difference in their speeds is more than about 15 km/h on a flat road, this becomes the biggest drain on the rider’s energy.
3. Rolling Resistance
Bike tyres deform under the weight of bike and rider as the rubber comes into contact with the road surface. Because the tyre doesn’t spring back with quite the same energy as it had when it deformed, this shape-changing absorbs a small amount of the energy, which, in the main, has been put into the system by the cyclist pressing on the pedals. A hard tyre on soft ground suffers from similar rolling resistance, although this time it’s the ground that deforms, once again absorbing the rider’s energy.
Friction helps to move the bike forward by maintaining contact between tyre and road and is crucial for forward motion. Without it the wheel would spin on the spot, as if on ice. However, friction in the bearings of the bicycle’s drivetrain – from the pedals through to the chain, gears and hubs – can absorb up to 5% of the cyclist’s energy.
Riders must also overcome inertia, which is not a force at all, but an innate property of matter – its resistance to any change in its state of motion. What this means is that an object doesn’t change its motion unless there is a force acting on it. The bigger the force, the greater the change in motion (in speed or direction). Steep hills, strong winds, muscular legs and powerful brakes overcome inertia to the greatest degree. Mass determines how big the effect will be – under a particular force, a heavy bike will change its motion more slowly than a light model. Likewise, a rider who loses weight will be able to accelerate more quickly.
Which factors most affect riding speed?
Once a cyclist exceeds about 15km/h, most of their energy is used to overcome air resistance – and it doesn’t get any easier the faster they ride. The power required to overcome drag is roughly proportionate to the cube of their speed so, for example, if you double your speed you need eight times as much power.
Professional cyclists have teams dedicated to identifying every potential time-saving tweak the riders can make to help them go faster. You may not have that support structure, but below are some of the adjustments you can make and the average improvement they could make to a 40km ride time.
+5 mins 05 secs: Going from time trial bars to hands on brake hoods
+25 secs: Gaining 3kg of weight (from 70kg to 73kg)
-13 secs: Switching from riding a 10kg bike to riding a 7kg bike
-25 secs: Losing 3kg of weight (from 70kg to 67kg) to reduce drag area
-34 secs: Using an altitude training facility
-1 min 24 secs: Taking a pre-ride caffeine, carb and electrolyte drink
-4 mins 24 secs: Using an optimal aero-dynamic body position (see below)
-7 mins 18 secs: Changing from no training to training at maximum effort
The Best Position for Maximum Speed
A rider’s position on the bike accounts for about 65-80% of their total aerodynamic drag. Even without an aero helmet, any rider can improve aerodynamics by flattening their arms, torso and head and tucking in their elbows. This may mean they deliver less power to the pedals, but this is usually offset by the reduction in aerodynamic drag.
When riding a bike with drop handlebars the least effective position is with hands on top of the bars, but moving forwards to rest on the brake hoods makes the body crouch a little, reducing frontal area and air resistance. The best shape is achieved with hands right down on the drops.
Aero bars allow the rider to cycle with their arms out straight and achieved worldwide popularity after the US rider Greg Lemond used them in the final stage of the 1989 Tour de France. Under the rules set by cycle sport’s governing body Union Cycliste Internationale (UCI) aero bars are permitted in some, but not all, cycling events.
NEXT: Get Fitter By Cycling
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