Originally Posted by
kingston
Yes. That's why the range is 16-19 mph. Rough estimates, the pace tends to drop about 1% for every 5 feet/mile over 25. So most people will be about 15% slower on a course with 100 feet/mile than a course with <25 all else equal, so someone who can average ~19 on a flat course will likely drop to ~16 when there's 100 feet/mile.
Really depends on the kind of route the 100 feet per mile is on also. Steady regular uninterrupted climbs with descents you can actually bomb is a LOT faster route than an in-town ride with 100 feet per mile of constant turns, stop signs at the bottom of hills, and things slowing you down.
IMHO, most fondos tend to be ideal average speed scenarios. You get breaks. The turns are marshalled as are stop signs and lights. Most route design is for easy descending without weird blind dead stop hairpins. In the flat parts you're nose breathing and chatting for long stretches doing 100w at 25+ mph as the peloton shrieks along. Lose a group? There's another.
Other posters talking about 1min and 5min power are correct. You won't get away on TT power at most flatter races around here, you'll get towed back. But, it's about being able to dig at 1min power after already doing threshold for a couple minutes or recovering and doing it several times. Except for hobbyists in TT, 20min power and longer doesn't really matter a lot in slower amateur racing. So long as you have a good enough "base" that when you're sitting in the group you're recovering and not still working.
Same for group rides. You need some more overall fitness if just sitting in the rotation is painful and you're not recovering.