[PAR_WIG1350]

The issue is reliability, you can tension 25 chain properly, but then it stretches and falls off, with 35 chain, some stretching is more acceptable and doesn't need to be adjusted as much. If weight is your focus, and you have no issues getting things tensioned properly, than timing belts may be a better option as they don't stretch (depending on the material), but they aren't always as strong or reliable either.