Oil-filled geared differentials are the standard in the majority
of 1:8 nitro-powered vehicles. They are strong and reliable, and
can handle the power from a highly tuned 3.5cc engine with ease.
Generally, the only maintenance required is to clean and re-oil,
whilst the only tuning available is to alter the viscosity or thickness
of the oil to increase or decrease the resistance of the action.
Most competition models nowadays come as standard with regular
geared diffs, following the proven design model of two sun gears
on the outside with four smaller planetary ones sitting between
them. Silicon oil inside the casing not only lubricates the gears
but also is a powerful tuning aid – so as to increase the differential
action or reduce it depending on driving style and track conditions.
However, on most tracks, setting up your diffs in this manner ultimately
becomes a compromise with the car handling better in some corners
but becoming more of a handful in others as the corner speeds and
diff actions are affected by whether the power is being applied
at the time, how hard it is being applied or whether the car is
under a trailing throttle condition (off-power). What the SmartDiff
promises is to overcome much of this compromise by offering the
best of both worlds through clever design.
The new SmartDiff is designed to be used in Losi competition models
like the 8ight and 8ight-T derivatives. Off-power, the SmartDiff
works just like a regular differential filled with very light oil
so the action allows for the car to be very nimble and agile. Under
acceleration, the SmartDiff locks up to enable the power to be
transmitted equally to the two driveshaft outputs reducing the
risk of doffing out if one output loses traction compared to the
other. As you come off the power again for the next turn, the differential
action returns to enable good turn-in characteristics.
Unlike using silicone oil to tune the on/off power characteristics
of the diff (a heavier oil gives better on power acceleration but
compromises off-power steering), the SmartDiff, gives you the best
of both worlds – good on-power performance whilst maintaining that
The SmartDiff uses grease inside it for lubrication rather than
oil so you can imagine that the diff action is very light and easy.
Losi supply some alternative springs that changes how hard the
SmartDiff locks and when it happens. This means that it is possible
to delay the locking action and make it smoother by using a harder
spring that offers more resistance or to use a soft springs to
allow the diff to tighten up earlier and lock out earlier.
The new Losi unit is an easy direct replacement for either the
stock centre or front items and can be fitted to every 8ight-based
model without any additional modification required.
Early testing by the team seems to confirm the theory with top
drivers reporting that the car is now even more consistent to drive
with more off-power steering without sacrificing on-power acceleration
resulting in quicker lap times. An additional benefit when using
the centre SmartDiff is that now, the action of the centre diff
can be tuned without affecting the brake bias feel unlike before
whereby the use of really thick silicone oil would require a different
bias setting as opposed a thinner oil.