I agree with the guy above who said it is fit and rider position. The biggest factor in how fast a bike/rider combo will go by far is rider fitness followed closely by rider position on the bike. If you can cruise at 18mph sitting upright in the wind then getting into a horizontal "aero" riding position will automatically put two or three mph onto your speed. Once you have a bike that is the right size and you are able to ride in that aero position, then most future improvements in speed will come from training. A very fancy bicycle and accessories all working together which will cost thousands of dollars might be worth a few more mph, but without a strong rider as a pilot, even the latest bicycle built with the latest racing technology will not go fast enough to win any races, and even if used for touring it will be passed up by a strong rider on a much older bike.