ChrisF
ArboristSite Guru
When you are standing next to an oak/maple/ash/birch/elm/popple waiting to be limbed and bucked, up to your nutz in snow (literally), you'll know why 20" is the most common logging bar around here.
Snow and ice change the game. You aren't walking to gracefully on ice covered timber with broad limbs, most limbing is standing on the ground.
Less cost, Less weight, less teeth to sharpen, less chance of throwing a chain, less chain to stick in the snow and hit rocks/dirt/ice with(hot chain can temper in the snow and ice), less bar and chain smaller area needs to be stamped down around the base of the tree to drop it (falling cuts are made low), cut fast in northern hardwoods coupled with a 70cc saw.
I am out of breath.
In short, weather conditions/terrain/type and size of timber dictate the bar you'll use.
This is what I've seen as true as well. That, combined with the fact that the trees don't get very thick (comparatively) in Norway means 20" of bar will do everything I need it to.