Handlebar Preparation
From Pvdwiki
Preparing mountain bike handlebars is quite simple, but easy to do wrong.
Cut to Length
I cut my example to about 25.5" These bars will be going onto a singlespeed, so a little wider is better. On a geared bike, I would cut them about an inch or so narrower.
Cutting handlebars too narrow results in extremely poor handling and leverage against the terrain. Leaving the bars too wide results in bumping trees or bridges too much, plus you are limited in terms of narrowest crossings.