Truly flat roads with no stop signs I generally average 23 - 24 MPH in the drops for 30 - 45 minutes, of course that is at the edge of arobic riding. When I am pushing I can actually cruise at 25 MPH + but I am definitly hitting the upper limits on anarobic work. I am a very very strong rider on the flats, at 6'6" I can develop lots of power when I need too... just need to work on hills.
I have always been a time trial person but I am just getting into criteriums. I hear from some people that the average in a 4 corner criterium can be 27 MPH+...
that is the average.
I can not say if you need to be able to do 24 MPH to be competitive in a crit, I am just speaking from experience. I will have a little more information after Sunday when I finish my first crit. Let me say for all the speed on the flats I am not a climber at all, Some of my normal training routes with steady climbs I am averaging 16 - 17 MPH depending on the route. Remember that averages are based on a lot of factors, just because one person can average 24 MPH does not make him more fit then someone at 19 MPH unless the routes are exactly the same. As they have said there are alot of factors in average speed. A few training routes I can go 5 miles without having to slow down, that really pushes the average. On a normal 60 mile training ride my average generally approaches 20 - 21 MPH. It all depends on your body type. My night group ride pushes 25 - 26 MPH at times if not faster in a paceline but the average is low (about 19 MPH) because of the climbing we do and all the starts and stops.
I remember pulling a 5 person break at 24.5 MPH up this 3 percent grade and after 3 minutes being tired and anarobic... it all depends. I have gotten extremly strong in the last month after entering the build period of my race training this season. Put me with some of these guys I rode with last night (cat 4 and cat3) 1 month ago and I would be dropped so fast. During base this year I was only averaging 17 MPH on training rides. 19-20 MPH where you are is awsome.
I would not say I am in increadable shape, I just work hard. I ride 6 days per week, typical week is about 150 - 170 miles when it is warm outside (60 mile long enduance ride, 40 - 50 mile fast club ride, 2 20 - 25 mile race paced club rides, and 2 days of intervals, 20 or so miles) and one day off. I have heard all kinds of numbers thrown around, one says if you can run 30 MPH in a pace line taking your pulls you can be competative in CAT 4,5. Some say if you can run 25 MPH in the drops by yourself you can be competative in CAT5. The only way to find out is to go and race. I am doing that this week (finally)...