2. Pedaling power
When cycling, your speed depends upon your pedaling power (Ppe) and the resistance that you must overcome using that power. At a constant speed, 4 components make up that resistance:
1. the intrinsic resistance of the bicycle (Rb)
2. the rolling resistance (Rr)
3. the air resistance or drag (Rd). And during a climb:
4. the slope resistance (Rsl).
The relationship between the pedaling power, the various resistances and the speed can be shown in a model (figure 1). We use this model to compare the speed of a recumbent high racer with that of a regular racing bicycle on a level road and during a climb or descent. In the model, the pedaling power (Ppe) is the drive of the bicycle. This drive must overcome a number of resistances, resulting in speed or velocity (v). Pedaling power is measured in watt, speed in km/hour; but in calculations the speed is expressed in meters per second.
Figure 1 From pedaling power to cycling speed
pedaling power (Ppe), intrinsic resistance (Rb), rolling resistance (Rr),
air resistance (Rd), slope resistance (Rsl) and speed (v)
Approx. 5% of the pedaling power of a regular racing bicycle is needed to overcome the intrinsic resistance of the bicycle (Rb); this is approx. 7% for the recumbent high racer (see the next chapter).
And so: Pb = 0.05 × Ppe and Pb = 0.07 × Ppe, respectively. The portion of the pedaling power that is required to overcome the rolling resistance (Rr) is calculated as: Pr = m × g × Cr × v (1)
Overcoming the air resistance (Rd) requires: Pd = 0.5 × ρ × A × Cd × v³ (1).
When climbing, the pedaling power needed to overcome the slope resistance (Rsl) is: Psl = m × g × % × v (1).
In these formulas, the mass (m) equals the ready-to-ride weight of the bicycle in kg plus the ready-to-ride weight of the cyclist; the gravity (g) equals 9.81 m/s²; the rolling resistance coefficient (Cr) has no dimension. The letter d stands for drag (air resistance), the Greek letter ρ (roo) for the relative density of the air; at sea level, it is 1.23 kg/m³, at a height of 1800 m, it is 1 kg/m³ (1). A (area) is the front surface of the cyclist plus bicycle in m²; Cd is the air resistance coefficient, which is a dimensionless number and a measure for streamlining. The slope is expressed as a percentage (%) during climbs and descents. The formulas are explained in more detail in the following chapters.
For speed comparison on a level road, during climbs and descents, we select a regular racing bicycle with a weight of 10 kg ready-to-ride (figure 2). It is compared to an equally heavy recumbent high racer (figure 3). Both bicycles have the same 28 inch wheels and the same tires, enforced with kevlar against puncture. The rider on both bicycles is a non-competitive cyclist, with a ready-to-ride weight of 75 kg. Dry and smooth asphalt paving without bumps and cracks is assumed in the calculations and it is always calm weather during cycling. All of the distances on both bicycles are solo rides without crashes or punctures. The reported pedaling power and speed in the calculations are average values.
Figure 2 Regular racing bicycle made of steel, ready-to-ride weight 10 kg
(Photographie L’Alpe d’Huez)
Figure 3 Recumbent high racer made of carbon, ready-to-ride weight 10 kg
(photo M5 Ligfietsen)
Various power meters are available for measuring pedaling power (Ppe); but these are still expensive and are used almost exclusively by professional cyclists. In the SRM-system (Schoberer Rad Mess-system) (figure 4), strain gauges measure the pedaling power between the crank and the chainring (4). A small computer on the handlebars then calculates the pedaling power. The price of a SRM-meter ranges between 2,000.- to 3,500 euro (in 2017).
Figure 4 SRM Wireless Training System (2)
Garmin and Look Keo have also introduced power meters on the market (figure 5). These measure the pedaling power in the pedal spindles (2). This makes it easy to switch the meter over from one
bicycle to another. The current price is approx. € 1,150-. Also the speed is shown on the accompanying bicycle computer.
Figure 5 Garmin Vector Power pedals (1)
Pedaling power and speed
On a level and smooth asphalt road under calm weather conditions, the non-competitive cyclist on a regular racing bicycle, with his hands positioned in the drop handlebars, reaches a speed of 17.1 km/hour with a pedaling power of 50 watt (table 1). The speed on the recumbent high racer on that same road and with the same pedaling power reaches 19.9 km/hour. At 500 watt, the speed is 44.3 and 54.7 km/hour for the regular and recumbent racing bicycle, respectively. The calculations are explained in the chapters to come. Given the same pedaling power, the high racer is always faster than the racing bicycle on a level road. The difference increases from 16.4% at 50 watt to 23.5% at 500 watt (table 1 and figure 6).
Table 1 Pedaling power and speed (km/hour) on a level road
|17.1 ||23.6 ||28.0 ||31.4 ||36.7 ||40.8 ||44.3|
|19.9 ||28.3 ||33.9 ||38.3 ||45.0 ||50.3 ||54.7|
|+16.4 ||+19.9 ||+21.2 ||+22.0 ||+22.6 ||+23.3 ||+23.5|
Figure 6 The increase in speed in relation to an increasing pedaling power is non-linear
Speed and pedaling power
Conversely, the pedaling power that is needed to reach a certain speed differs between the regular racing bicycle and the recumbent high racer. The pedaling power required to reach a speed of 10 km/hour on the regular bike is 19.7, but only 17.5 watt on the high racer; a difference of 11.2% (table 2). If the speed exceeds 40 km/hour, then the pedaling power on the regular bicycle must be at least 40% higher in order to compete with the recumbent bicycle. A speed of 50 km/hour requires a pedaling power of 697.7 and 393.7 watt, respectively; a difference of 43.6%. And so the difference in terms of the required pedaling power between the regular racing bicycle and the recumbent high racer increases with speed (figure 7). The calculations are explained in the chapters to come.
Table 2 Speed and pedaling power (watt) on a level road
|19.7 ||178.6||697.7 ||1814.5|
|17.5 ||113.7 ||393.7 ||979.1|
|-11.2 ||-36.3 ||-43.6 ||-46.0|
Figure 7 The increase in required pedaling power is non-linear
Pulling on the handlebars
In reality, the difference in speed between the regular and recumbent racing bicycle is smaller than shown in these tables and figures. The reason is that the same cyclist can develop a higher pedaling power in a regular position than recumbent. Pulling on the handlebars of a regular racing bicycle is probably a more efficient way to transmit power to the pedals than pushing your back against the bucket seat of a recumbent bicycle. On the high racer, pulling on the handlebars (with its construction being what it is today) has no influence on your pedaling power. To achieve that, the stem of the handlebars should be shorter and its angle in the headset should be smaller (figure 3). The only recumbent bike in which pulling the handlebars is an essential component of the drive concerns the so-called ‘rowing bicycle’. This pulling is so efficient that strong cyclists can pull up with the back wheel skidding. A few have even managed to successfully complete La Marmotte (a French climbing classic) on such a rowing bicycle. To my knowledge, no other recumbent cyclists have ever accomplished that.
Continuous pedaling power
How much pedaling power can the same cyclist develop in one hour on a regular racing bicycle, and how much on a recumbent high racer? No comparison of that kind has been made so far. It is estimated here that the 1-hour pedaling power of a recumbent cyclist is approx. 20% lower compared to the regular cycling position. Thus a non-competitive cyclist who can pedal a maximum of 225 watt on a regular racing bike for one hour will probably not exceed 180 watt on a recumbent high racer. Such a difference in pedaling power compensates roughly half of the difference in speed between the two bicycles. Thus any race on a level road between cyclists on regular and recumbent racing bicycles would still be unequal. The decision of the UCI (Union Cycliste Internationale) not to allow such ‘mixed’ competitions is therefore understandable.
1. Pedaling power generates bicycle speed by overcoming the intrinsic resistance of the bicycle, rolling resistance, air resistance and (during a climb) slope resistance.
2. The recumbent high racer is faster than the regular racing bicycle at the same pedaling power on a level road; this difference exceeds 20% if the pedaling power exceeds 100 watt.
3. The recumbent high racer requires less pedaling power than a regular racing bicycle to achieve the same speed; this difference exceeds 40% at speeds higher than 40 km/hour.
4. The 1-hour pedaling power of a cyclist is an estimated 20% lower on a recumbent compared to a regular racing bike because the recumbent cyclist cannot pull on the handlebars.
1. Wiel van den Broek: Technische artikelen over de fiets: Vermogen en Krachten, juni 2013. http://www.velofilie.nl/vermogen.htm
2. Jeroen van Geelen: Garmin Vector Power pedalen: Power to the people, aug. 2011. http://www.triathlon226.nl/2011/08/
3. SRM Wireless Training System, juli 2013. https://www.srm.de/store/index.php?cat=c1_Training-System.html&XTCsid=62de95bdbf0042439ac6e8284e227638
4. Guido Vroemen: ‘Watt it takes’;Vermogensmeters als hulpmiddel voor de fietstraining. Triatlon duatlon sport, febr. 2008.
© Leo Rogier Verberne