Recumbent trikes, like recumbent bikes, have an extended distance between the chain rings and the freewheel or cassette, due to the position of your feet in front of your body rather than below. As a result, the chain length on a recumbent trike is considerably longer than that of an upright bike, though it is similar in function to that of recumbent bikes.
Length
Chain length on a recumbent trike depends greatly on design, including factors such as the length of the wheelbase, the vertical position of the cranks and the position of the gear cassette. In general, recumbent trikes need the equivalent of two or even three lengths of standard bicycle chain.
Considerations
A few trikes with two wheels in front have the cassette on one of the front wheels, with the pedals positioned ahead of the front wheels so the chain stretches back to the cassette. These models have short chain lengths compared to other trikes.
Design
Most trikes have a 2-inch wheel called an idler that guides the chain back toward the rear gears. This piece doesn't exist on regular bikes with standard chain lengths. In addition, on long chain trikes, the chain runs through stiff tubes in the long sections between chain rings and cogs to protect it from tangling, swaying and debris. The longer chains and need for chain tubes on recumbent trikes contribute to their generally higher weight than upright bicycles. Recumbent trikes are not always heavier than their two-wheeled cousins, recumbent bikes.
Gearing
The wider the range of gears on a recumbent trike, the longer the chain will need to be. According to the Bicycle Tutor website, the correct length of chain is the minimum needed to wrap the chain around the largest front chain ring and the largest rear cog at the same time, without threading the chain through the dérailleurs, plus one inch or about one extra complete link.
Warning
The chain line on a recumbent trike should be as straight as possible and not touch the frame even when the trike is bouncing around on bumps in the road. A skewed chain line puts more fatigue on the chain and requires you to exert more force to pedal your trike.
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