I hope I don't sound stupid, but I want to buy a road bike. I want to start riding back and forth from work and back. 10 miles each way.
I am way out of shape....I am 5'7" and weigh around 190...
I want to try to get down to 175, so I can get the stress off of my knee. I had 2 surgery on the knee, so I hope this will also strenghten.

Question 1) What size would I need.
Q2) I want to get a complete used bike.
Q3) Should I get steel, alum, carbon, material frame?

What else do you recommend?

Naoya

I am 5'9" and my 54 fits me beautifully, so I'd say a 54, but go to a local shop that specializes in road bikes and they will be able to give you a better idea. If you really want to get a good fit, pay for a professional fitting and they will put you on an adjustable frame type of deal and get you the correct frame, stem, seat height, crank length, bar width, etc... A professional fitting is typically about 150. At the very least, test ride a few different sizes and you will get a good idea of what feels good for you.

As far as material, it all depends on what you like. I prefer aluminum, some love steel. My next roady will be carbon. Steel and titanium will be more compliant, I get a good bit of flex in the bottom bracket on my aluminum Cannondale, but I can deal with it. Steel is the most rigid. Carbon fiber is pretty stong too, but if you damage it in a crash, its pretty much toast. I have not ridden a Ti frame, but I'd love to try out a Lightspeed or Lynskey.

Good luck with your purchase, keep us posted.