Operator`s Manual RM1
Seite/page 122/132 ROTAX KART RM1 Ausgabe/Edition 01/2006
6.1.3. Choice of gear ratio
The 125 Max DD2 engine in spite of its 2 gears offers a broad performance band. Therefore the
frequent changing of gear ratios, as you are used to with 1-speed engines, is not necessary.
Note: It is not possible to change the 1
st
and 2
nd
gear individually.
On most of the Kart circuits you will be well served with the standard gear ratio (35 : 62 which is
equivalent to 12/90 for 1
st
gear and 14/79 for 2
nd
gear).
If due to the special shape of the circuit (e.g. extremely sharp corners or long straights) it should
seem necessary, the gear ratio can be changed both to a shorter or a longer ratio.
The diagram (acceleration potential) depicts that the engine has its optimum acceleration potential
between 9.200 and 12.200 r.p.m. /min. It should therefore be operated in this range, overreving up
to 13.600 r.p.m. is possible.
BESCHLEUNIGUNGSPOTENTIAL
ACCELERATION POTENTIAL
0,00
2,00
4,00
6,00
8,00
10,00
12,00
14,00
16,00
18,00
20,00
22,00
24,00
26,00
3.000
4.000
5.000
6.000
7.000
8.000
9.000
10.000
11.000
12.000
13.000
14.000
15.000
Motordrehzahl [1/min.], engine revolutions [rpm]
Motordrehmoment [Nm],
torque of engine [Nm]
großes
Beschleunigungspotential
high acceleration potential
Kurve des Fahrwiderstandes
graph of driving resistance
When the engine speed exceeds 12.200 r.p.m. the torque drops and in consequence the
acceleration potential, therefore you should shift from 1
st
into 2
nd
gear at 12.200 r.p.m.
Note: The maximum speed is limited at 13.800 r.p.m. by an electronic r.p.m. limiter.
If the r.p.m. range from 9.200 to 12.200 r.p.m. is not sufficient due to a particular track shape
(extremely long straight) the maximum engine speed of 13.600 r.p.m. should be aimed for.
Note: A basic requirement for the full use of the speed range between 12.200 to 13.600
r.p.m. is optimized carburetor jetting (see chapter Carburetor Adjustment).
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