Originally Posted by bensanford

I find that fixed is vastly different from single-speed and prefer fixed. It is easier to climb in a higher gear on fixed-gear than on a freewheel bike. Since the pedals move forward when the bike is moving, it helps the pedals push through the dead spots at the top and bottom of the pedal stroke, so I can climb slopes on fixed at 69-gear inches, where I would probably shift down to something like 42-24 or 42-26 if climbing the same slope on a regular road bike. I generally use about 69 gear-inches on the road when on fixed-gear - so I have 42-16 on one bike, and 44-17 on another. I shifted to a higher gear (44-18) on a long relatively flat ride to better keep up with other road bikes.

If using a freewheel on a single-speed you are somewhat forced to ride a lower gear to climb, and that makes it even more difficult to keep up on the flats.

Regardless, keeping up with the road bikes will also depend a lot on the terrain. Rolling hills (even short and steep) are much better that longer slopes. Keep the horizontal wavelength short . Mile long climbs or Decents would be a problem keeping up on the downhills. Tailwinds would also pose a problem.

Riding fixed generally forces you to attack the hills - keeping your momentum up from the downhills to get up the next slope, and that means being able to spin at high cadences. In excess of 150 RPM is possible for short periods...