Do you mean cruising speed or do you mean average speed over your commute, including stop lights and stop signs? I'm much like you if you meant average speed over your commute, including stops and delays. But, if you meant cruising speed (on the flat, stable, at the level of effort you are willing to use), then I think 13 mph could be a factor of engine or equipment. You can manage the engine as you want. As a first remedy, I'd make a friction inspection (no dry idler bearings, no flat spots on idlers, no tight or clogged chain tubes, clean and lubricated chain and chainrings, no dry seals in the hubs, no dirt or crunchies in the hub bearings or bottom bracket, etc.). My typical average speed is 12-13 mph for commuting, but I probably have a cruise speed more in the 17-18 mph range (although Indianapolis is way flat compared to Lanco so its possible the rolling vertical nature of Lanco roads is also slowing you down somewhat, despite the notion of gaining back on the downhill side what you lost on the uphill).
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Longbikes Slipstream