Bicycle performance
Bicycle performance is measurable performance such as energy efficiency that affects how effective a bicycle is. Bicycles are extraordinarily efficient machines; in terms of the amount of energy a person must expend to travel a given distance, cycling is calculated to be the most efficient self-powered means of transportation.
The transport performance of bicycles is also exceptional in terms of ton kilometers. In terms of the ratio of cargo weight a bicycle can carry to the total bike weight, cycling is also the most efficient means of cargo transportation.
Mechanical efficiency
From a mechanical viewpoint, up to 99% of the mechanical energy delivered by the rider into the pedals is transmitted to the wheels, although the use of gearing mechanisms reduces this by 1–7%, 4–12%, or 10–20%. The higher efficiencies in each range are achieved at higher power levels and in direct drive or with large driven cogs.Energy efficiency
A human traveling on a bicycle at, using only the power required to walk, is the most energy-efficient means of human transport generally available. Air drag, which increases with the square of speed, requires increasingly higher power outputs relative to speed. A bicycle in which the rider lies in a supine position is referred to as a recumbent bicycle or, if covered in an aerodynamic fairing to achieve very low air drag, as a velomobile.According to a study a human at requires about 60 watts to walk at on firm and flat ground, while according to a calculator at kreuzotter.de the same person and power output on an ordinary bicycle will travel at, so in these conditions the energy expenditure of cycling is about one-third that of walking the same distance. Uphill and downhill speeds vary according to the slope of the incline and the effort of the rider. Uphill cycling requires more power to overcome gravity and speeds are therefore lower and/or the heartrate is higher than during flat riding conditions. With medium effort a cyclist can pedal 8–10 km/h up a gentle incline. Riding on grass, sand, mud, or snow will also slow a rider down. Without pedaling downhill a bicycle rider can easily reach speeds of 20–40 km/h down a gentle 5% slope and speeds exceeding 50 km/h on steeper inclines.
Energy output
How much power humans can generate and for how long varies with physical form. The specific power may be expressed in watts per kilogram of body mass. Active cyclists can produce from 1.0 W/kg 2.2 W/kg, 3.0 W/kg, and 6.6 W/kg at their functional threshold power. 5 W/kg is about the level reachable by excellent male or exceptional female amateurs. Maximum sustained power levels during one hour are recorded from about 200 W to 500 W. For a day's pedalling these figures can roughly be halved, for a minute's duration doubled.Energy input
The energy input to the human body is in the form of food energy, usually quantified in kilocalories or kilojoules . This can be related to a certain distance travelled and to body weight, giving units such as. The rate of food consumption, i.e. the amount consumed during a certain period of time, is the input power. This can be measured in kcal/day or in J/s = W.This input power can be determined by measuring oxygen uptake, or in the long term food consumption, assuming no change of weight. This includes the power needed just for living, called the basal metabolic rate BMR or roughly the resting metabolic rate.
The required food can also be calculated by dividing the output power by the muscle efficiency. This is 18–26%. From the example above, if a 70 kg person is cycling at 15 km/h by expending 60 W and a muscular efficiency of 20% is assumed, roughly 1 extra food is required. For calculating the total food required during the trip, the BMR must first be added to the input power. If the 70 kg person is an old, short woman, her BMR could be 60 W, in all other cases a bit higher. Viewed this way the efficiency in this example is effectively halved and roughly 2 total food is required.
Although this shows a large relative increase in food required for low power cycling, in practice it is hardly noticed, as the extra energy cost of an hour's cycling can be covered with 50 g nuts or chocolate. With long and fast or uphill cycling, the extra food requirement however becomes evident.
To complete the efficiency calculation, the type of food consumed determines the overall efficiency. For this the energy needed to produce, distribute and cook the food must be considered.
Typical speeds
In utility cycling there is large variations in speeds reached. An elderly person on an upright roadster might do less than while a fitter or younger person could easily do twice that on the same bicycle. For cyclists in Copenhagen, the average cycling speed is. The fitness and cadence of the rider, bicycle tire pressure and sizes, gear ratios, slope of the terrain affect the overall speed of the rider. A person pedalling with 100 W power can achieve 5.5 m/s on a roadster, 7.5 m/s on a racing bicycle, 10 m/s with a faired HPV and 14 m/s with an ultimate HPV. In competitive cycling a sustainable high speed is augmented by the use of light materials, low-resistance tires, aerodynamic design, and the aerodynamic effects of the peloton. The group can maintain a higher speed over extended distance due to various cyclists taking turns at the head of the wind then dropping behind to rest. A team time trial produces the same effect.Fitness cyclists use a speedometer or cyclocomputer to measure, record, and share several variables including speed, gradient, distance, time, cadence, slope, power, temperature, GPS data, route, and even heart rate.
Cycling speed records
The highest speed officially recorded for any human-powered vehicle on level ground and with calm winds and without external aids is set in 2016 by Todd Reichert in the Eta Speedbike, a streamlined recumbent bicycle. In the 1989 Race Across America, a group of HPVs crossed the United States in just 5 days. The highest speed officially recorded for a bicycle ridden in a conventional upright position under fully faired conditions was over 200 m. That record was set in 1986 by Jim Glover on a Moulton AM7 at the Human Powered Speed Championships during Expo86 World Fair in Vancouver. The fastest bicycle speed in slipstream is 296 km/h, set by Denise Mueller-Korenek in 2018 on the Bonneville Salt Flats. This involved slipstreaming behind a dragster.Cycling speed wobble
Dangerous steering wobble or shimmy may occur at high speeds, and also lower speeds with frames with high flexibility coupled with inadequate damping.Reduction of weight and rotating mass
There has been major corporate competition to lower the weight of racing bikes in order to be faster uphill and accelerating. The UCI sets a limit of 6.8 kg on the minimum weight of bicycles to be used in sanctioned races.Advantages of reduced mass
For cycling on the level at a constant speed, a large weight reduction saves only a negligible amount of power and it is on the contrary beneficial to add mass in the form of aerodynamic improvements. But for climbing steeply, any weight reduction can be felt directly. E.g., a reduction of 10% of the total system weight will save nearly 10% power.A reduced mass is also directly felt when accelerating. For example, the gives a time/distance advantage of 0.16 s/188 cm for a sprinter with 500 g lighter wheels. In a criterium race, if a rider has to brake entering each corner, then this is wasted as heat. For a flat criterium at 40 km/h, 1 km circuit, 4 corners per lap, 10 km/h speed loss at each corner, one hour duration, there would be 160 corner "jumps". For 90 kg rider and bike, this adds roughly one third effort compared to the same ride at a steady speed, and a mass reduction of 10% of the total system weight could thus give about a 3% advantage.
Advantages of light wheels
The mass of tires and rims must be accelerated linearly and rotationally. It can be shown that the effect of rim and tire mass of typical spoked wheels is effectively doubled. Reducing their mass is thus especially noticeable in the case of sprints and corner "jumps" in a criterium.Power required
There are well-known equations that give the power required to overcome the various resistances mainly as a function of speed and operational parameters.Air drag
The power ' needed to overcome air drag or resistance is:where
The concept of apparent wind is only directly applicable here if it comes from a true headwind or tailwind. Then is the scalar sum of and the headwind or the difference between and the tailwind. If this difference is negative, must be regarded as assistance rather than resistance. If however the wind has a sideways component, the apparent wind must be calculated with a vector sum and, especially if the bicycle is streamlined, the calculation of lateral and drag forces becomes more complex; a proper treatment involves considering the forces on the surfaces like the forces on sails.
The drag coefficient depends on the shape of the object and on the Reynolds number, which itself depends on '. However, if ' is the cross sectional area, ' can be roughly approximated as 1 for usual cycling speeds of a rider on an upright bicycle.
Rolling resistance
The power for overcoming the tires' rolling resistances is given by:where is gravity, nominally 9.8 m/s^2,
is the slope, and is mass.
The approximation can be used with all normal coefficients of rolling resistance. Usually this is assumed to be independent of although it is recognized that it increases with speed. Measurements on a roller-mechanism give low-speed coefficients of 0.003 to 0.006 for a variety of tires inflated to their maximum recommended pressures, increasing about 50% at 10 m/s.