IAME REEDSTER 125cc Assembly Instructions & User Manual page 37

The following example should clarify the procedure for optimization of sprocket ratio :
assume to use an engine, in the F4 version with a Z=12 sprocket, and that during the
preliminary track tests a Z=78 teeth axle sprocket has been used.
From the table 1 with Z=12 as engine sprocket and Z=78 on the axle sprocket , a
ratio of 6,5 is found.
Make a few laps on the track and let us assume that you read a max. of 12500
engine RPM .
From table 2, to achieve a max. RPM of 13500 (operating limit for F4 engine
version) a sprocket ratio from 7,08 and 6,96 should be used (having used during
the tests, a sprocket ratio of 6,5 and having achieved 12500 RPM).
From table 1, with these values, a sprocket ratio of 12:85 or 12:83 should be used
or having a Z=11 on the engine sprocket, a ratio of 11:77 should be used.
SPROCKET RATIO TO ACHIEVE MAX. 13500 RPM (F3 e F4)
Max Engine
RPM during
tests
Sprocket ratio
35 MAN-051 ING