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 agility.

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.