Pan cars are two wheel direct drive, so the motor pinion meshes with the spur that is directly attached to the rear axle, so you just need to worry about the gear ratio and the size of your rear tires to give you the rollout
TCs are 4wd so the pinion meshes with a spur that is attached to the center layshaft. From there you have layshaft pulleys which connect to the differential pulleys, usually by belts. So you need to factor in the ratio of the differential pulleys divided by the layshaft pulleys to give you the internal ratio. You take the gear ratio (spur divided by pinion) and multiply it by the internal ratio to give you the Final Drive Ratio.
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