Drivetrain lab

Formula: (spur ÷ pinion) × internal reduction = final drive ratio. With the motor held at the displayed RPM, wheel RPM is motor RPM ÷ final drive ratio. The gear animation uses the external spur ÷ pinion ratio only; internal reduction happens downstream. Gear diameters are schematic, not to scale. The 15T / 57T / 2.85 example aligns with a current ARRMA listing that identifies 15T pinion, 57T spur and 2.85 internal ratio; this lab is an original calculation, not a specification lookup. Source.

Rear 2WD: the rear axle is driven; the front wheels roll freely.

Drive configuration says which axles receive power. It does not say whether an axle differential is open, locked or limited-slip. Many 4WD designs add a center transfer or center differential; a current 4X4 ARRMA listing, for example, specifies a center differential. Source.

An open differential allows different wheel speeds in a turn. Its fixed-carrier constraint is that the two axle speeds average to the carrier speed.

For a locked axle in this simplified model, left and right wheel speeds are equal. On split grip, an open differential generally transmits roughly equal torque to both outputs, with usable drive limited by the lower-grip side—not literally “all torque” going to the spinning wheel. A lock can improve progress but resists the speed difference a corner needs, increasing turning radius. Traxxas describes the independent wheel speed of an open differential and the turning-radius trade-off of locking one. Source. ARRMA also identifies its traditional assembly as “open differential action.” Source.