I am not rich so the budget is as low as possible. I use my bike for pleasure mostly as I am still a teenager. Of course I want speed, so I was wondering how well it would work if I changed the tires to thinner then they already are. Please tell me what size would be good, I ride on the road often, but I also use the sidewalk enough that a standard 700c tire would have to much vibration. I was also thinking about switching the handlebars to road bike style. Thanks in advance