| what can be Learned from "The Vehicle Performance Curve" |
| From the foregoing, the three correlations in the vehicle performance curves -Engine Speed and Vehicle Speed, Running Resistance and Tractive Effort -are clear. They are reproduced in Graph 15. The horizontal axis expresses vehicle speed. The vertical axis on the left expresses both tractive effort and running resistance, and on the right vertical axis indicates engine speed. These two vertical axes are not correlated with each other. For example the 1,500kg on the left axis is in no way correlated with the 3,000rpm on the right. For sake of convenience, the graph was made this way to eliminate the necessity of referring to separate graphs. From these performance curves various performance characteristics of the vehicle can be read. |
Graph 15
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| Maximum Speed |
As explained in section on the relationship between vehicle speed and engine speed, maximum speed can be read from the running performance curve. The maximum speed of the vehicle illustrated in Graph 15 is 100km/h.
However, if the running resistance on a level road is substantial as shown by the hypothetical dotted curve in Graph 15, and if the vehicle is running in fifth gear, the running resistance will equal the tractive effort (point  ), and vehicle speed cannot be increased beyond this point. In other words, under these hypothetical circumstances, the actual maximum speed is 92km/h instead of the rated 100km/h. |
| Gradabillty - Hill Cilmbing Performance |
The gradability listed in the catalogue is for the first gear and shows the gradient at which maximum tractive effort equals running resistance. To get the gradability of the first gear, read the % value of the running resistance line tangent to the peak of the tractive effort curve.
In the case of the first gear, the running resistance line tangent to the peak of the tractive effort curve is not shown. However, if a line parallel to the 25 and 30% lines is drawn tangent to the peak of the tractive effort curve, it will be located midpoint between the 25 and 30% lines. Consequently, the tangent will be at point áA on Graph 15 with a value of 27.5% |
| Gradabillty - Hill Cilmbing Performance |
According to Graph 15, the tractive effort of the vehicle running at 40km/h in 3rd gear is about 870kg (point  ). When climbing a 3% grade, the running resistance it encounters is 465kg (point  ). The difference between the tractive effort and running resistance is the surplus tractive effort: |
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This surplus of tractive effort will enable the vehicle to accelerate and negotiate rough road conditions when necessary. When the gear is shifted from 3rd to 4th, the tractive effort is reduced to 555kg (point  ) and the surplus tractive effort is lowered by 90kg: |
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This leaves hardly any margin of tractive effort for acceleration, when needed.
From the above, it is evident that the greater the surplus tractive effort, the greater is the versatility and handling ease of the vehicle. |
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