You can cut up to 36" with an 18" bar on those rare instances. IMHO tough to beat two good mid sized saws with identical bars and chains. I'd much rather have 10 sharp chains and two bars and sharpen the chains at my leisure. Longer bars rob hp from the engine and tire your back sooner.
I recall a log I cut a few years ago on a local beach.... used my 16” bar and at a diagonal even....then later to discover that that tree, a very high probability that it drifted down the Yukon, had been alive and standing when the Mayflower landed a ‘few’ years previous. Being a tough old bird doesn’t require great size, not does it mean that you’re even a match for a basic Poulan, (though I’m not promoting that color for durable use. 😬)
