whats the normal crank size for a 20"???
It’s sort of personal prefrence, I think 140’s would be a good choice, thats what I ride. They give you the right amount of torque in my opinion.
IMHO, I feel that 140 gives you a lot of torque, but are too slow. I know that trials is not about so much about “riding” as hopping, but it’s a pain in the arse to have such huge pedal strokes when riding flat ground. Personally, I would prefer to have 130 mm cranks on my trials.