Although allowable deck stringer spans have changed a bit over the years, why are they always given as a specific number without regard for the stringer to stringer spacing like rafters and joists? I am building a set of deck stairs with 8 risers using 2x12s. I am using composite treads that require stringers 10″ on center.  Shouldn’t the allowable stringer span be greater than if I was using some other tread material that only required 16″ on center?