I had a quick search and if I found the right hill (A504?) it seems to be about 0.5 km at 10%? If so, then sorry - that's just a
'London reality check'!
I got a West Yorkshire reality check on this climb ('Mytholm Steeps') when I first started cycling up here ...
I got up the 10% bits which led into the 14% bits as a prelude to the 18% bits and I even managed to get up this 25% ramp ...
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The problem came when I was coming to the evil bend where that black car is in the photo above. The bend steepens to probably 35+% so the only way for a normal human being to be able to cycle round it is to be pull out into the middle of the road and take it wide.
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Unfortunately a moronic nobber driver cut me up and forced me onto the inside of the bend where those cobbles are. I came to a dead stop and couldn't unclip in time to stop myself toppling over. Fortunately, I fell left onto the grass, not the other way.