700x35 to 700x28 on My Hybrid?

I'm thinking about changing the stock 700x35 tires on my hybrid bike (Trek 7000) to 700x28 so I could go faster and hopefully more comfortably.



Will this make much of a difference? How much easier will it be to ride? I average about 15mph right now, but I'm wondering how much faster I'd go with 700x28.Do I need to change the tubes also? Anything else I should know?700x35 to 700x28 on My Hybrid?
If your current 35 is knobby or has a large tread pattern designed for road and gravel/packed trails you may speed up a bit with a 28, which has a road only tread pattern. Your ride will most likely be a bit less comfortable as you are reducing the amount of cushioning space between the rim and the road with a smaller tire. When I switch from 35 to 28s on my cyclocross bike I can feel the bumps in the road a bit more. The ride is also a bit faster for me. Maybe a mile or two per hour faster. My 35s have a packed knobby type tread and the 28's are pure road tread.