I am considering a new bike for triathlons. I have riden a lot of different set-ups, but I have been most comfortable with a road bike fitted with Thomson set-back seat post turned around to get forward, and then aerobars -- either clip-on or a full aero set-up.

My best ride has been on a Trek... various models within their 5000 series. I guess if I went with a new one though, it would be with a Madone. However, their new seatpost won't let me use a "forward" seatpost.

For that reason, to ensure that I can get far enough forward for my liking, I've started looking at Specialized, the other roadie brand carried by my local bike shop.

Can someone give me a rundown of the major differences I will encounter between the Tarmac and the Roubaix?

FWIW, I live in a very hilly area of west-central PA and typically do most of my training and racing around here. And as mentioned above, I really like to be forward with my seat position.

I am also wondering about sizing of the Specialized realtive to the Trek. I have riden both 54 and 56 with the Trek and have been able to be comfortable on both of the sizes. Is there much difference with Specialized relative to being stretched out or scrunched in?

Thanks for all your help and advice!

Ray Doolittle