3. Intrinsic resistance
Figure 1 From pedaling power to cycling speed
pedaling power (Ppe), intrinsic resistance (Rb), rolling resistance (Rr),
air resistance (Rd), slope resistance (Rsl) and velocity (v)
Friction occurs in the moving parts of a bicycle, particularly in the chain and the guiding sprockets, the bearings and axles (bosses). That makes up the intrinsic resistance of a bicycle. As a result, part of the pedaling power is lost as heat and cannot be converted into speed. The friction of the chain on the front plate and on the small rear sprocket costs ± 2% of the pedaling power (1); bearings and axles cost ± 1%. This brings the intrinsic resistance of a perfectly serviced track bicycle (figure 2), meaning without gears and derailleur, to ± 3%.
Figure 2 Time trial bicycle on the track: a single sprocket on the rear axle (Chris Boardman/Getty Images)
Regular racing bicycle
Both, a regular racing bicycle and the recumbent high racer, have a cassette on the rear axle, usually with 10 sprockets (2). Guiding the chain to the sprocket of your choice (switching gears) requires a derailleur, which also has two small sprockets (figure 3). These are responsible for an additional ± 2% loss of pedaling power. So a well serviced regular racing bicycle has an intrinsic resistance that causes a loss of pedaling power of approx. 5% (Pb = 0.05 × Ppe). The loss is greater if the bicycle has not been properly maintained, causing more laboured pedaling.
Figure 3 Cassette with 10 sprockets and a derailleur; chain length ± 1.35 m
Recumbent racing bicycle
The recumbent high racer and the regular racing bicycle that we are comparing are both equipped with the same ‘group’ of moving parts. But the chain of a recumbent bicycle is almost three times as long. This requires extra guidance using a chain roller and suspension to prevent swaying (figure 4). This generates extra friction and an additional loss of pedaling power of approx. 2%. This brings the intrinsic resistance of the high racer to ±7% (Pb = 0.07 × Ppe).
Figure 4 Chain roller and chain suspension high racer; chain length ± 3.75 m
The difference in intrinsic resistance between a regular and recumbent racing bicycle can be measured on a roller (figure 5). To that end, the pedaling power must be the same on both bicycles (50 watt, for example), when measuring the speed that is reached. Because the bike is virtually standing still, there is no air resistance (Rd). And there is no slope resistance (Rsl) either as you need not move a weight upwards. Thus, the speed developed on the roller depends entirely upon the intrinsic resistance of the bicycle (Rb) and the rolling resistance (Rr). The latter (Rr) is the same in both, the regular and the recumbent racing bicycle (see next chapter). And so the difference in speed between the two bicycles depends solely upon the intrinsic resistance. If the Rb is 5% for a regular racing bicycle and 7% for the high racer, then you will measure a difference in speed of 2% on the roller. On the open road, the speed that is achieved on both bikes at the same pedaling power is totally different because air resistance is dominant on the open road. Which differs considerably for the two bikes, even with the same rider and the same pedaling power.
Figure 5 Roller type Galaxia (photo Tacx)
1. The intrinsic resistance of a well serviced regular racing bicycle causes a loss of pedaling power of approx. 5%; this is estimated to be 7% for the high racer.
2. The higher intrinsic resistance of the high racer is the result of the extra guidance that is needed for the much longer chain.
3. The difference in intrinsic resistance between two bicycles with the same rolling resistance can be measured on a roller.
1. Wiel van den Broek: Technische artikelen over de fiets: Vermogen en Krachten, juni 2013. http://www.velofilie.nl/vermogen.htm
2. Wikipedia: Cassette (fiets). http://nl.wikipedia.org/wiki/Cassette_(fiets)
© Leo Rogier Verberne