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REGULAR versus RECUMBENT cycling

Leo Rogier Verberne


Summary


Various bicycles
There are approx. 20 million bicycles in the Netherlands, ± 50,000 of these being recumbent bikes. The types of recumbents available are highly divergent and only a few can be compared to a regular racing bicycle. The recumbent carbon 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


Massive spills during road races on regular racing bicycles may result in permanent disability or even death. These accidents occur so frequently that professional racers feel it is ‘all part of the game.’ When riding in regular position the head is protruding; when riding recumbent the feet are protruding and take the hit in case of a crash or spill. Furthermore, in recumbent position any pressure on the genital organs by a slim bicycle saddle is lacking. And the workload of the heart is less during physical strain in a lying position.

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 bicycle. 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 the blood does not flow back to the heart as easily as it does on a recumbent bicycle. 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. This prolonged pressure does not occur when cycling recumbent.

B.Speed


My own experience revealed that riding recumbent on a level road is faster than riding a regular racing bicycle on the same road. But climbing steep slopes was nearly impossible on a recumbent bicycle. How to explain that varying speed difference between both bikes?

B 1. Pitfalls
Competitions between cyclists on regular and recumbent racing bicycles mainly compare the cyclists. A comparison of the bicycles qua speed requires the same cyclist on both bicycles (paired observations) and the same pedaling power. Therefore a power meter is needed instead of a heart rate monitor, because the heart rate is higher when cycling in a seated position compared to cycling recumbent with the same pedaling power. Another pitfall in the comparison concerns the estimate of the air resistance (front surface and Cd, meaning streamline): errors in these estimates 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 it is much faster on its descent. Moreover, preconceptions that exist among participants and/or researchers may influence the outcome of the comparison between a regular and a recumbent bicycle.

B 2. Pedaling power

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)

The pedaling power of the cyclist generates the speed of the bicycle. That power must overcome the intrinsic resistance of the bicycle, rolling resistance, air resistance and (during climbs) slope resistance. 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- (Rb), rolling- (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 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. Pressing your back against the back of 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. Accurate measuring is essential as the difference is a mere 2%.

B 4. Rolling resistance
The rolling resistance depends upon the weight of the bicycle with its rider, the rolling resistance coefficient (Cr), the speed and the road surface. 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 tires that are more inclined to warp. On a level and dry asphalt road, at a speed of 30 km/hour, a touring cyclist 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 bicycle is the low racer, having the same ready-to-ride weight (10 kg). But that low racer has a 20-inch front wheel and a 26-inch rear wheel. The pedaling power required 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 (49/42) than is the case for the recumbent high racer at the same speed. 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 bicycle. 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 on a recumbent high racer is estimated as 0.2 m². Therefore, his air resistance is lower by half on the recumbent bicycle. That’s why, for an average speed of 30 km/hour on a level road, this touring cyclist needs one third less pedaling power on the recumbent high racer compared to the regular racing bicycle.

B 6. Climbing
When riding a recumbent bicycle, you cannot pull on the handlebars to increase your pedaling power. Therefore you could compare climbing on a recumbent high racer to riding a regular racing bike ‘with no hands’. The steeper the slope, the lower the 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, the tilting point being an 1,5% slope. As a result, the touring cyclist is still 11,5% faster when riding recumbent on a level road; however, when climbing an 8% slope he is 20,4% slower on the recumbent high racer than climbing the same slope on a regular racing bicycle.

B7. Descending
Upon descending, without pedaling or braking, our touring cyclist is faster on the recumbent bicycle than on the regular racing bicycle (with his hands positioned in the drop handlebars). The difference in speed of descent between both bicycles is ever growing with an increasing steepness of the slopes. However, the relative difference in speed is a constant 41% on all slopes when descending under the same standard circumstances. Because there is no pedaling when descending, the difference in pedaling power of the same cyclist on both bicycles is out of order. The same applies to the difference of intrinsic resistance between the regular and the recumbent racing bicycle: if there is no pedaling, there is no friction in the chain. And the rolling resistance is the same in both bicycles. Thus the difference in speed when descending the same slope, is solely caused by the difference in air resistance between both bicycles.

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 racing bicycle with an average pedaling power of 225 watt can gain 5 seconds in time (0.1%) across a distance of 50 km with 1 kg less weight. When climbing a 10 km long 8% slope, he will go faster by 36 seconds (1%) thanks to that 1 kg weight loss. But when descending (with his hands in the drop handlebars), the same weight loss will take 4 seconds more time of descent (0.7%).

C.Tour de France


The exclusion of recumbent cyclists from official cycling races makes a direct confrontation of regular and recumbent competitive cyclists impossible, for example in the Tour the France. The correct comparison of a regular and a recumbent racing bicycle needs the same competitive rider on both bikes, the same cycling route and equal weather conditions, that’s to say a model Tour.

C 1. Model Tour
The 100th Tour de France of 2013 serves in here as a model for the theoretical comparison of a regular and a recumbent racing bicycle, with Chris Froome as the rider on both bicycles. But the recumbent bicycle has 2 kg more weight and its intrinsic resistance is 2% more, both being disadvantages for the recumbent high racer relative to the regular racing bicycle. Moreover, the pedaling power of Froome on the recumbent bicycle is an estimated 20% lower. He rides all of the stages in the model Tour solo without spills or punctured tires. The road surface is smooth and dry, the weather conditions are always calm. In the hill stages all slopes are 4%, in the mountain stages they are 8%. In the model Tour all sections between the hills and mountains are flat.

C 2. Regular versus recumbent cycling
In the level stages of the model Tour, Chris Froome is 8,7% faster when riding recumbent than riding regularly; although the recumbent bicycle is 2 kg heavier and its intrinsic resistance is 2% more; and on top of that, Froome’s pedaling power is estimated 20% smaller when riding recumbent. However, when climbing 4% and 8% slopes, Froome is 9% and 19,5% slower, respectively, on the recumbent compared to the regular racing bicycle. But when descending, without pedaling or braking and when riding recumbent, he is 24% faster both on 4% and on 8% slopes. And thus, across the entire route of the model Tour, Froome is 3,8% faster on the recumbent bicycle and his final time is 3h 10' 37" less than riding his regular racing bicycle. If all of the participants in the real Tour de France 2013 had rode a recumbent bicycle, with the exception of Froome, and if all of them, as a result, had realized a 3,8% shorter final time, then his winning final time on the regular racing bicycle in 2013 would have ranked him in 112th place (of all 169 participants).

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© Leo Rogier Verberne
ISBN/EAN:978-90-830515-1-2
www.recumbentcycling.org