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RECUMBENT versus REGULAR RACING BICYCLE

Leo Rogier Verberne



Summary


Various bicycles
There are approx. 20 million bicycles in the Netherlands, ± 50,000 of these being recumbent bicycles. The types of recumbent bicycles available today are highly divergent and only a few can be compared to a regular racing bicycle. The recumbent high racer is the most similar because it has the same wheels and a ready-to-ride weight of 10 kg. Which makes it best suitable for a comparison to a regular racing bicycle.

A. Health

A 1. Heart rate
At the same level of physical exertion, that is to say that you are generating the same pedaling power on both bicycles, your heart rate when sitting on a regular racing bicycle is higher than it is on a recumbent high racer. The oxygen supply and blood flow are the same on both bicycles indeed, but equal cardiac output requires a higher heart frequency when seated. Because then the blood does not flow back to the heart as easily as recumbent. As a result, the heart is less filled when seated and the stroke volume is lower. A higher heart rate does compensate for that lower stroke volume, but it also means a higher workload of the heart.

A 2. Sexual organs
When exerting oneself in a bent forward cycling position on a regular racing bicycle, sweat trickles down the back along the anal cleft. Intestinal bacteria and Candida are present around the anus and flow down, with the sweat, infecting the sexual organs. In women, this may lead to a vaginal and/or a bladder infection. These infections may also be caused by the contaminated penis of a cycling partner. Moreover, the sexual organs of both men and women can become numb as a result of the prolonged pressure exerted by the saddle. In males, this may result in impotence and prostate problems. Which is not happening when cycling recumbent.

B.Speed

B 1. Pitfalls
Competitions between cyclists on recumbent and regular racing bicycles mainly compare the cyclists. A comparison of the bicycles qua speed requires the same cyclist and the same pedaling power on both bicycles (paired observations). Therefore a power meter is needed instead of a heart rate monitor, because the heart rate is higher when cycling seated than cycling recumbent with the same speed. Another pitfall in the comparison concerns the estimate of the air resistance coefficient (Cd): minor errors in the estimate have major consequences for the calculated speed. And when comparing the two bicycles during climbing, descents must be avoided. Because a recumbent bicycle climbs slower than a regular racing bicycle, but is much faster on its descent. Moreover, preconceptions that exist among participants may influence the outcome of the comparison between a recumbent and a regular bicycle.

B 2. Pedaling power
The pedaling power of the cyclist generates the speed of the bicycle. That power must overcome the intrinsic resistance of the bicycle, the rolling resistance, the air resistance and (during climbs) the slope resistance.

Figure 1 From pedaling power to bicycle speed

diagram tour

pedaling power (Ppe), intrinsic resistance of the bicycle (Rb), rolling resistance (Rr),
air resistance or drag (Rd), slope resistance (Rsl) and speed (v)

A bicycle computer on the handlebars can be used to read the pedaling power (Ppe) and the speed (v). The portion of the pedaling power that is required to overcome the intrinsic resistance (Rb), rolling resistance (Rr), air- (Rd) and slope resistance (Rsl), respectively, can be calculated. In the case of the same cyclist and equal pedaling power, the recumbent high racer is faster on a level road compared to a regular racing bicycle. This difference increases from more than 16% at 50 watt pedaling power to almost 24% at a pedaling power exceeding 500 watt. However, the same cyclist can generate less pedaling power on a recumbent than on a regular racing bicycle. Pushing your back off from the bucket seat of a recumbent bike is most likely less efficient than pulling on the handlebars of a regular racing bicycle to transmit pedaling power to the pedals. Reliable measuring is required.

B 3. Intrinsic resistance
The intrinsic resistance of a well maintained regular racing bicycle causes a loss of pedaling power of approx. 5%; that loss is an estimated 7% on a recumbent high racer. This difference is due to the chain of the recumbent bicycle, which is almost three times as long and requires extra guidance to prevent swaying. And that guidance causes friction. The difference in intrinsic resistance can be measured on a roller, if the rolling resistance of both bicycles is the same. Accuracy in measuring is essential as the difference is a mere 2%.

B 4. Rolling resistance
The rolling resistance depends upon the road surface, weight of the bicycle and its rider, the rolling resistance coefficient (Cr) and speed. The Cr-value is determined by the size of the wheels and the type and the pressure of the tires. Optimally inflated tubes have a lower Cr-value than thicker tires that are more inclined to warp. On a level and dry asphalt road, at a speed of 30 km/hour, a person weighing 75 kg will require a pedaling power of 42 watt to overcome the rolling resistance. That is valid for the regular racing bicycle as well as the recumbent high racer, both with the same ready-to-ride weight of 10 kg and the same 28-inch wheels.
A comparable recumbent racing bicycle is the low racer, with a front wheel of 20 inch and a rear wheel of 26 inch. The pedaling power to overcome the rolling resistance of this bicycle for a 75 kg weighing rider at a speed of 30 km/hour, is 49 watt. Which is 17% more than is the case for the recumbent high racer at the same speed (49/42). So larger wheels run lighter.

B 5. Air resistance
In order to overcome the air resistance (drag), you need approx. 27 times (3³) more pedaling power at a speed of 30 km/hour compared to a speed of 10 km/hour. This applies to both the regular racing bike as well as the recumbent high racer. A non-competitive cyclist weighing 75 kg and with an average build has a front surface of approx. 0.4 m² on a regular racing bicycle when his hands are positioned in the drop handlebars. His front surface is ± 0.2 m² on a recumbent high racer. Therefore, his air resistance is only half on the recumbent bicycle.

B 6. Climbing
When riding a recumbent high racer, you can neither pull on the handlebars (with the construction of the handlebars being what it is today), nor stand on the pedals. Therefore you could compare climbing on a recumbent bicycle to riding a regular racing bike with no hands. The steeper the slope, the less climbing speed. Thus the advantage of lower air resistance when riding recumbent is ever declining with increasing slope. However, the disadvantage of an estimated 20% less pedaling power for the recumbent cyclist remains constant and starts to prevail with increasing slope. As a result, the difference in cycling speed between the recumbent high racer and the regular racing bike (both equal in weight) varies from +11.5% on a level road to -20% when climbing an 8% slope.

B7. Descending
Upon descending (without pedaling or braking), the cyclist’s lower air resistance on a recumbent bicycle remains dominating because pedaling power is out of order. As a result the difference in speed of descent between the recumbent and regular racing bicycle (with the rider’s hands positioned in the drop handlebars) is ever growing with increasing steepness of the slopes. However, the relative difference in speed is a constant 41% on all slopes. In order to reduce air resistance, professional cyclists lie flat along the upper tube of the racing bicycle when descending steep slopes. In this ‘ski-position’, the front surface is an estimated 0.3 m². Compared to the riding position with hands in the drop handlebars, this increases the speed of descent on a 8% slope by about 15%.

B 8. Weight and speed
On a level road and in a climb, more weight at the same pedaling power results in some loss of speed. It does not matter whether the weight gain is caused by the bicycle, the cyclist or the baggage. The relationship between this total weight and bicycle speed is linear both on a level road as well as during climbs and descents. On a level road, a 75 kg non-competitive cyclist on a 10 kg regular racing bicycle with an average pedaling power of 225 watt can gain 5 seconds in time (± 0.1%) with 1 kg less weight across a distance of 50 km. When climbing a 10 km long 8% slope he will go faster by 36 seconds (1%) by that 1 kg weight loss. But descending (with his hands in the drop handlebars) the same weight loss will take 4 seconds more time of descent (0.7%).

B 9. Tour de France
The question is whether or not a professional cyclist could win the Tour de France on a recumbent bicycle. To answer that question, the Tour of 2013 serves as a model. We compare a 8 kg regular racing bicycle to a 10 kg recumbent high racer (both ready-to-ride weights). In addition to the disadvantage of 2 kg more bicycle weight, the 1-hour pedaling power of the professional on the high racer is an estimated 20% lower. The cyclist on both bicycles is Chris Froome, the actual winner of the Tour in 2013. His ready-to-start body weight is 70 kg, his 1-hour pedaling power on the regular racing bike is estimated at 450 watt. Which means that his 1-hour pedaling power on the high racer is limited to 360 watt. The weather in the model-tour is always calm, the road surface smooth and dry. All of the stages are solo rides. However, the time trials are not considered, because a special bicycle is used for these trials, which falls outside the scope of this comparison.
The level stages each will take 4 to 5 hours cycling time. When considering the pedaling power in the course of a 5-hours period, 80% of the 1-hour value seems the max, even for a well-trained champion like Chris Froome. So his 5-hours pedaling power value on the regular racing bicycle is 0.8 × 450 = 360 watt. With that, he achieves in the level stages an average speed of 41.55 km/hour. On the recumbent high racer, his 5-hours pedaling power is also 80% of the 1-hour value, so 0.8 × 360 = 288 watt. That brings his average speed in the level stages to 45.16 km/hour. That is 8.7% more. The climbing of each hill or mountain takes less than one hour and is followed each time by a descent, being a period of relative rest. Thus during climbing Froome can reach his 1-hour pedaling power on both bicycles. Thus, on the high racer he is 9% and 19.5% slower in 4% and 8% uphill strokes respectively, than on his regular racing bicycle. But in all descents (without pedaling or braking) he is 24% faster on the recumbent high racer. On balance, across the entire route of the model-tour, he is 3.8% faster on the recumbent compared to the regular racing bicycle. If all participants in the actual tour of 2013 had rode recumbent high racers and if, subsequently, they all had been 3.8% faster, then Chris Froome’s winning final time on the regular racing bicycle would have ranked him in 112th place.

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© Leo Rogier Verberne
ISBN/EAN:978-90-825495-1-5
www.racefiets-ligfiets.nl


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