My hybrid came with 700c X 38 touring tires and the effect was like dragging a brick behind the bike. Once I switched to 700c X 25 with slick tread there was a noticeable improvement in the speed department. Losing weight (off your body, not necessarily your bike) seemed to make a large difference for speed improvement also. I've also placed drop style bar ends on mine which seemed to boost my speed just a tad. But, my hybrid is still slower than my road bike. I like to think of it as a touring bike instead.