Originally Posted by
caloso
My commute is much shorter than yours, but I notice that the only thing that makes any appreciable difference on time is whether the stoplights are in my favor. Doesn't matter if I ride my race bike or my old mountain bike.
This is my finding, too, with city riding, except that the absence of a headwind helps, as does having a tailwind. In other words, there may not be much you can do.