If you look at racing cyclists riding you will see that they pedal far higher rpm's than you would be doing at 25mph in a 50-12 gear (roughly 70 rpm). I have seen that people with heavier legs sometimes tend to spin slower, but sprint cyclists often have huge legs and still spin. I raced Cat3/4 in the 70's and never had over a 100 inch gear (52/14) yet one crit I raced in had a 29mph average. Most racers would consider "spinning out" to be well in excess of 120 rpm. It's not your gearing holding you back. A larger chainwheel (higher gear) increases your speed for a given rpm. It does not allow you to maintain that rpm.
Lastly, no matter what speed you go spinning is more efficient. When you pedal slower the hard, off-center pedaling tends to create wasteful flexing of the bike and pushes you off a straight line track. The more anaerobic muscle effort does not allow your circulation to supply your muscles fuel and carry away waste as well over an extended ride. The only time you would be pushing a higher gear at lower revs is out of the saddle accelerating or hill climbing.
In any case "It's the rider, not the bike," is as true now as it ever has been.As alluded to above the odds of you ever being able to "average over 30mph" are nil. One hour for a 25 mile time trial is considered very good time, even for an elite rider.
Last edited by cny-bikeman; 08-08-10 at 05:45 PM.