Polaris SUPERSPORT 2006, Manual

Page: 152 / 300

7.8
CLUTCHING
BACK-SHIFTING
Back-shifting occurs when the track encounters an increased
load (demand for more torque). Back-shifting is a function of
a higher shift force within the driven clutch then within the
drive clutch. Several factors, including riding style,
snowmobile application, helix angles, and vehicle gearing
determine how efficient the drive system back-shifts. The
desired engine operating RPM should never fall below 200
RPM when the drive system back-shifts.
FINAL GEARING
The final drive gear ratio plays an important role in how much
vehicle load is transmitted back to the helix. A tall gear ratio
(lower numerical number) typically results in lower initial
vehicle acceleration, but a higher top-end vehicle speed. A
lower gear ratio (higher numerical number) typically results in
a higher initial vehicle acceleration, but a lower top-end
vehicle speed.
Choosing the proper gear ratio is important to overall drive
system performance. Lowering the final drive gear ratio will
compress the MPH scale between the low and high ratio lines,
while raising the final drive gear ratio will expand the MPH
scale between the low and high ratio lines.
When deciding on which gear ratio to use, the operator must
factor in the decision where the snowmobile will be ridden,
what type of riding will be encountered, and the level of
performance the operator hopes to achieve.
Gearing a snowmobile too low for extended high-speed runs
may cause damage to the drive belt and drive system, while
gearing a snowmobile too high for deep-snow, mountain use
may cause premature belt and clutch wear.
Typically, it is recommended to gear the snowmobile with a
slightly higher ratio than the actual top speed the snowmobile
will ever achieve.
1:1 Shift Ratio
A 1:1 shift ratio occurs when the drive clutch and the driven
clutch are rotating at the same RPM. In this mode, the drive
system is at its highest efficiency. Drive system efficiency
falls off past the 1:1 shift ratio.
The mathematical vehicle speed for a given gear ratio at a 1:1
shift ratio is represented in the chaincase gearing charts
located in the Final Drive Chapter.
LOW / HIGH RATIO LINES
The low ratio line is the mechanical position when the drive
belt is all the way down into the drive clutch, and all the way
out on the driven clutch. The high ratio line represents when
the drive belt is all the way out on the drive clutch, and all the
way in on the driven clutch.
Note that the high ratio line is past the ideal 1:1 shift ratio.
DRIVEN HELIX / RAMP
The helix cam is the primary torque feedback component
within the driven clutch, regardless of driven clutch type. The
beginning angle of the helix must transmit enough torque
feedback to the moveable sheave in order to pinch the drive
belt while minimizing belt slip. The flatter or lower the helix
angle, the more side force will be exerted on the moveable
sheave, while the steeper, or higher the helix angle, the less
side force will be exerted on the moveable sheave.