Here is something i found written by John Summerson
Tenth of a mile
Canton Ave.
Pittsburgh--35%
When this short street first comes into view, you will simply not believe how steep it is. Rising more aggressively than the more famous Fargo Street in Los Angeles, Canton is, as far as I've been able to determine, the steepest paved 10th of a mile in the world. The city of Pittsburgh officially lists it at 37 percent, but my multiple measurements indicate 35 percent overall from bottom to top, with a maximum of 37 percent. Cars are prohibited from driving down it, and a common pastime for those who live near its base is watching automobiles try to climb it in bad weather. On a bike, even with a flying start, almost all cyclists end up needing to tack from side to side to reach the top, even with mountain bike gearing. Adding insult--or glory, depending on your point of view--the second half of Canton is paved with cobblestones. All of this makes Canton a treasured part of the Dirty Dozen, an annual unofficial race that climbs 13 of the city's toughest streets (dannychew.com). Get There: Turn onto Canton from Coast Avenue in the Beechview section of Pittsburgh
Assuming that to be true for a second, the total altitude gain would be 56 meters. It can be seen in the video mentioned earlier that the first guys climb it in 19 seconds, which means almost 3 meters/s, ie about 3 horsepower for 75 kg (man + bike), more than Zabel could ever muster and an impressive velocity of 30 km/h.
Then assuming a gear ratio of say 36:21, they would be spinning at over 135 rpm, definitely not the impression you get ( more like 60-80 rpm)
Anybody from Pittsburgh who can tells us a bit more?