Some mechanics

In order to better understand what the advantages and disadvantages of recumbents (and of the Nordic Trike) are, we want to deal with some bicycle physics. School physics is already enough for this, and besides, we hardly use not any formulas here. If you want to have it more precisely with formulas, and calculate it on the computer itself, you can download the spreadsheet programs below.

Dependence of manpower from speed

When someone rides on the bike, their body must have a certain power (in watts). If you drive faster, more power needs to be applied. If the driver's cardiovascular rushes to its limits, the maximum manpower is reached at the latest. This depends on the driver and sporting training condition. Typical maximum manpower are:

Children and seniors: up to 150 W,

Adults (tourist level): up to 250 W,

Sporty riders: up to 350 W

Professional cyclists: up to 450 W

When the driver pedals this manpower, it overcomes several types of resistances:

Driving resistance: due to rolling friction: depends on the overall weight and rolling resistance of the tyres (air pressure, tyre tread, wheel diameter, little dependent on the number of wheels).

Air resistance: depends on the cross-sectional area of the bike with the rider, as well as on the driving speed and the headwind speed. In addition, the air resistance depends on the shape of the body (Velomobile therefore often have a sophisticated dozen-cold shape with very small air resistance).

Slope: If you drive uphill, the entire mass of drivers and vehicle must be transported uphill. This requires further manpower compared to the ride in the plain

Let us now consider three different vehicles:

a) Normal bike: rider 85kg, bicycle 15kg, --> weight 100 kg. High drag on the air by upright drivers, cross-sectional area of riders about 0.5 m2.

b) Bicycle with trailer: there are 10 kg for the trailer and 15 kg for the contents of the trailer (total weight 125 kg).

c) Recumbent bike (e.g. Nordic trike): rider 85 kg, recumbent bike 40 kg, luggage 15 kg, air resistance, depending on the body shape, significantly smaller than the bicycle. (total weight 140 kg).

1. Ride in the plain:
Up to a speed of about 20 km/h, all three vehicles drive roughly the same and could still be driven by children or senior citizens. Only more than 25 km/h does the smaller air resistance of the recumbent (like our Nordic Trike) becomes apparent. Good velomobiles need far less manpower over 25 km/h.
The recumbent bike is about 20% slower than a bicycle at 20 km/h at the same manpower (caused by more weight and therefore higher rolling resistance).

2. Ride on a climb with only 3%:
If there is a climb of only 3% uphill, our competitive athlete with 350 W still comes to about 25 km/h and a senior with 100 W drives around 10 km/h. The air resistance has no big influence, the 15-20% lighter bicycle is faster bythis amount.

Manpower for a specific speed in the plane

Manpower for a certain speed at 3% incline

If you want to explore more, you should download the corresponding spreadsheet program (power(velocity).ods) for your own calculations.

In summary, this small excursion regarding the Nordic trike shows us the following:

The Nordic Trike as an everyday vehicle driving up to 25 km/h does not have to be particularly streamlined, even simple body shapes (or only a front cockpit) are enough.

For group rides of Nordic Trike and bicycles, the trike is already in the plane by 15 to 25% slower at same manpower or the driver has to use more power. Uphill the trike becomes even slower and needs more gear reduction for slow trips down to about 3 km/h.

The recumbent bike is therefore comparable to a bicycle with a trailer.

Download:

Torque and power at the Nordic Trike

The Nordic Trike has pedal drive like any recumbent. Due to the almost horizontal pedaling position of the legs, however, slightly less pedalling is brought to the pedals than is the case with the bicycle. In the case of bicycle with downward pedal position, the leg weight increases the pedal power of the downward leg when the other leg is pulled up. If nothing is pulled up, both legweights compensate.
In the recumbent, a part of the leg is also moved up and down at each revolution, of which only a certain part can increase the pedal power when the other leg is withdrawn. In the recumbent wheel, there is a certain power loss per revolution due to the other pedaling position. We consider here only everyday case, i.e. Pedal drive without click pedals.
The specialty of the Nordic Trike is the additionally usable hand drive (for details see hand drive). It only connects to the chain via a freewheel when the arms are moved back and forth on the hand drive handles. A pedal rotation corresponds to a pre- and back movement of the handles. The manual forces are quite smaller than the leg forces on the pedals, but always two arms generate drive at the same time and that with every pre- and back movement.

With a few assumptions, the torque and drive power of the "biomotor" person can be roughly estimated:

mean foot force on pedal (one leg): 150 N

mean hand force (one arm) : 25 N

Estimated high-level leg weight (one leg): 8 kg

esteemed high elevated arm weight (one arm): 3 kg,

estimated decrease curve of the hand forces beginning at 45 rpm to zero at 120 rpm.

With these assumptions, the torque can be increased from 25 Nm to 30 Nm when starting up by hand drive. With typical travel frequencies of 60 - 90 rpm, the difference is slightly smaller.
The next two figures show the resulting performance characteristics of the "Biomotor" man with and without hand drive.

estimated torque with and without hand drive depending on the pedal frequency

Estimated powers without hand drive

Estimated powers with hand drive

With hand drive, the power dissipation also increases a bit due to the additional arm movements.
If a driver drives constantly at approx. 75 rpm and uses the hand drive, increases the maximum drive power. The maximum manpower to be applied by the driver rises from 150 to 180 W and the Nordic Trike races faster thanks to more power.
If the driver does not want to increase the manpower used when using manual drive, he has to do the following:

Without manual drive with e.g. 75 rpm and Manpower 150 W drive,

with manual drive at about 50 rpm and 150 W manpower at the same speed, which is achieved with shifting upwards by one to two gears.

The following conclusions can be drawn from this small calculations
The non-power performance that is not effective for driving can reach up to 10% of the manpower on the recumbent bike. With hand drive there are 1-2% in addition.
With the use of the hand drive, torque and drive power typically increase by 10 to 30%, the Nordic Trike is moving faster and the driver's organism has to run 10-30% more manpower.
If the driver wants to remain atthe same manpower when using hand drive, and even at the same speed, then shifting down is good for one to two gears.
This behaviour was confirmed in practical driving.

Nordic Trike

Ideas and Solutions for everyday velomobiles

Some mechanics

Dependence of manpower from speed

Download:

Torque and power at the Nordic Trike