Op
erator’s Manual ROTAX 125 MAX evo, Junior MAX evo, Mini MAX evo, Micro MAX evo
Pa
ge 46/58
Ed
ition 09/2016
In
principle, the transmission ratio should be chosen in a way that the engine is mainly operated in
a speed range at which the engine performance is well above the driving resistance.
The following chart (125 MAX evo) shows that the difference between the engine performance and
the driving resistance constantly increases at a speed range from 5000 to
9000 rpm, remains the same at a speed range from 9000 to 11500 rpm and decreases again at a
speed about 11500 rpm onwards.
The smaller the difference between the engine performance and the driving resistance gets, the
smaller is the excess of power and thus the acceleration potential of the engine.
The intersection between the characteristic of driving resistance of the vehicle and the
characteristic of engine performance indicates the peak rotational speed of the engine at the
chosen transmission ratio.
With the „longer“ transmission ratio of 12/72=6, the characteristic of driving resistance of the kart
intersects the curve of engine performance at 13000 rpm – with this transmission ratio the engine
will achieve a maximum rotational speed of 13000 rpm. This leads to a maximum speed of 110.5
km/h.
With the „shorter“ transmission ratio of 12/78=6,5 the characteristic of driving resistance of the kart
stays below the curve of engine performance over the whole speed range - with this transmission
ratio the engine will achieve a maximum rotational speed of 14000 rpm. This leads to a maximum
speed of 109.8 km/h.
¢ Attention: If a transmission ratio is chosen that results in a maximum rotational speed of
14000 rpm, it does not automatically mean that this leads to the best lap time. With
a fluent routing, even a “longer” transmission ratio with a lower maximum rotational
speed can lead to a better lap time.
K00292
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