I agree with Fredwina work up to a metric. It is a big accomplishment in itself if you have never done one and FUN!! It is my favorite distance, so I am biased.

You can ride any bike for a century. I rode a heavy steel Fuji for my first and a couple MS150's. It was a more upright and a proper fit. This weekend I road my Cannondale, similar material and geometry to the Ruby. I had the same level of comfort as the old Fuji.

My husband rides a race, aggressive geometry bike. He was a little more sore at the end of the century even though he is in excellent shape and a stronger rider.

We were both well trained, so the next day just a little tightness in the quads. No real complaints.