I ride a hybrid. When I switched the tires from 35s to 28s, I noticed a significant difference. When my friend did the same, she noticed a big difference. So based on this experience, tires can make you faster. I rode my mountain bike during an event this fall that included a combination of dirt and paved roads. I wish I had ridden my hybrid (Giant Escape 1). The mountain bike (Schwinn MOAB) was way too slow for me. THe weight is about the same, but I feel the front suspension fork on the mountain bike really killed performance.