I have to say, that route is rubbish, but not for the same reasons as the op. Most of the roads ( with the exception of calthorpe rd) are quite narrow, so once they have the contraflow going it's going to be very difficult with hundreds of cyclist going up and down. I expect it will crawl to a near standstill in parts. The route last yr was really good (apart from one bit through the market) as the pershore rd is nice a broad and made the whole thing very spacious. I expect they got a lot of flak from various 'motoring' groups about that closure, so have gone for a much smaller route, which is a real shame as this is the only event in Birmingham using closed roads for kids to cycle on.
I did last yr's event with my two boys in a trailer, but will miss this as I'm doing a sportive in France.....hmm after today, maybe I should sport some Wiggo inspired 'burns' to annoy the locals
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EDIT : according to bikehike each lap is 6.44miles long (not the 6.6km the map states) and total ascent is 345 feet.