Choose Of Gear Ratio - Rotax 125 MAX DD2 evo Installation Instructions And Operators Manual

CHOOSE OF GEAR RATIO

In spite of its 2 gears, the 125 MAX DD2 evo engine offers a broad performance band.
Therefore, the frequent changing of the primary gear ratio is not necessary.
NOTE
It is not possible to change the 1
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
If due to the special shape of the circuit (e.g. extremely sharp corners or long straights), it
is deemed necessary, the primary gear ratio can be changed both, a shorter or a longer
ratio.
If the rpm. range from 9.200 to 12.200 rpm. is not sufficient because of a particular track
shape (extremely long straight), the maximum engine speed of 13.600 rpm. should be
aimed for.
NOTE
A basic requirement for the full use of the speed range between 12.200 to 13.600
rpm. is optimized carburetor jetting (see chapter 4.1. Carburetor calibration).
The acceleration potential between 9.200 and 12.200 rpm. is essentially higher than be-
tween 12.200 and 13.600 rpm. Therefore, it does not always make sense to use this rpm.
range (high top speed on a straight) and to not take advantage of the acceleration poten-
tial of the lower rpm. range (out of sharp corners).
This is a suggestion. The optimum choice can only be found with the exact knowledge of
the race track.
To approach and optimize the reduction gear ratio, the following charts should be helpful.
The optimization procedure regarding the reduction gear ratio for a new race track is ex-
plained step by step by the following example:
Procedure
Start with the standard gear ratio (35/62, equivalent to 12/90 at 1
gear).
Based on the following criteria, you must decide, whether a shorter or longer gear ratio is
necessary.
Does the engine reach 12.500 rpm in 2
IF YES, proceed
Procedure
as follows
Choose the next longer gear ratio (36/61 equivalent to 12/87 in 1
gear).
IF NO, proceed as Procedure
follows
Choose the next shorter gear ratio (34/63 equivalent to 11/87 in 1
2
.
3
Page 14
Edition: September 01 2019
Operators Manual
nd gear).
BRP-Rotax
st and 2 nd gear individually.
st gear and 14/79 for 2
nd gear at the end of the longest straight?
nd gear).
st gear and 14/79 at 2
st gear and 14/76 in 2
st gear and 14/83 in
Effectivity: 125 MAX DD2 evo
nd
nd