Be quick: http://www.wiggle.co.uk/challenge-elite-open-tubular-road-tyre/
Never had a good experience with Challenge tyres
If you want gum, have you had a look at the bont r4 320? mine running perfect...puncture free, but then cambridge is far from the conditions of london's famous london.
Neither did I, with the exception of the Strade Biancha which is very un-Challenge like.
@dan started
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Be quick: http://www.wiggle.co.uk/challenge-elite-open-tubular-road-tyre/