Technology: draft

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Technology: draft

Technology: draft
step by step

Whether a motorcycle has a passage like an ICE or a freight train depends on many influencing factors. MOTORRAD deals them step by step.

Waldemar Schwarz

07/09/2002

Durchzug, a word that leaves plenty of room for speculation. At the regulars’ table, for example, you can hear that two-cylinders have better pulling power than four-cylinders of the same displacement, motorcycles with large displacement pull better than low-displacement same power, V-engines push better than in-line engines with the same key data and so on. A number of factors play a decisive role in this.
According to the generally accepted definition, the torque is the acceleration in the last gear, a criterion that determines how relaxed a motorcycle can be. Rolling through a town in a large gear and accelerating again at the town sign without shifting gears or being able to overtake just by turning the throttle ensures relaxed motorcycle fun. A pleasure that is exemplified by three bikes: the super athlete, which is considered to be particularly powerful Yamaha YZF-R1, the massive all-rounder Suzuki GSX 1400 and the potent muscle bike Harley-Davidson V-Rod. These had to compete against each other in a direct comparison on the slopes for the draft measurement from 60 to 200 km / h.
Some theoretical considerations are required to explain the decisive factors in drafting. To push or pull an object, force is required, in the case of a vehicle, the so-called pulling force. It is generated by the torque of the engine and pushes the vehicle in the contact point of the rear tire. But before the torque from the crankshaft reaches the rear wheel as drive torque, it goes through several stages. In the primary drive, the gearbox and the secondary drive, the gear ratios and thus the amount of torque change.
For example, the power transmission transforms the maximum torque from 108 Newton meters of the R1 on the crankshaft to four to five times the value on the rear wheel, as well as the 105 Nm of the V-Rod and the 126 of the GSX 1400. In the range from 60 to 200 km / h, with the exception of a slack in the Suzuki between 60 and 80 km / h, all three are still almost the same with 400 to 450 Nm. While Yamaha and Harley alternate in the lead depending on the speed, the Suzuki even lags slightly behind despite the greatest torque because of its very long gear ratio (see diagram 1). The overall translation is therefore also decisive.
According to the lever law, the pulling force results from the lever arm of the rear wheel, i.e. its radius, and the drive torque on the rear wheel. Although still slightly superior in terms of drive torque, the V-Rod falls behind the Suzuki in terms of traction between 100 and 140 km / h due to the larger rear wheel diameter (diagram 2, dashed lines).
The tractive force must first overcome the driving resistance such as rolling and air resistance in order to accelerate the motorcycle. And they can be determined very precisely by means of roll-out tests. While the unclad V-Rod and GSX 1400 show similarly high values, the fully clad and therefore aerodynamically superior R1 has a significant advantage, especially in terms of air resistance, and slowly but surely sets itself apart from its pursuers. (Diagram 4, solid lines).
Because the tractive forces that the drive does not have to provide to overcome the driving resistance are available for the draft. Or to put it the other way around: After deducting the driving resistance forces, the tractive forces that can actually be used for propulsion remain. Here Newton’s axiom of mechanics comes into play, which expresses how much force is necessary to accelerate a mass. Or to put it simply: If a motorcycle still has a lot of tractive power after overcoming the driving resistance and it also has the lowest weight, it pulls through the best.
No wonder that the R1 relentlessly distances the competition. With 291 kilograms including driver and measuring equipment, it outclasses the GSX 1400, which weighs 350 kilograms in full habit, as well as the 375-kilogram V-Rod. In connection with the highest tractive power reserves (diagram 3), the R1 takes the GSX 1400 off a smooth five seconds when pulling from 60 to 160 km / h, the V-Rod even eight seconds. At higher speeds, the scissors gape further and further (diagram 4, solid lines).
The overall package consisting of engine torque, overall gear ratio, driving resistances such as rolling and air resistance and the mass is responsible for the pulling force. Since all parameters are recorded, it must also be possible to calculate the draft. At least approximately, because one variable, the mass moment of inertia of the rotating components from the crankshaft to the wheels, has not yet been taken into account. And finally, these parts also have to be rotated. Their angular acceleration requires an additional pulling force. However, it is only possible to measure the mass moment of inertia of the individual components with an enormous amount of effort.
If the rotating masses are neglected, the calculated values ​​are, as expected, slightly better than the measured values. The direct comparison (diagram 4) shows ?? despite never 100 percent constant external conditions such as wind or temperature influences ?? a surprising correspondence between theory and practice and proves that theory has to be anything but gray.
The most important thing about the phenomenon of pulling through remains of course: At full throttle, things have to go really well.

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