The Essex CTC SEG runs a Reliability Ride every February. It's 75 miles and traditionally ran from Lake Meadows, Billericay, up to Great Bardfield and back, in a "pair of spectacles" shaped loop. I think those two places were chosen as the whole ride was covered by a single 1:50000 OS map. In recent years it has started at Wickford, which seems to be at the convenience of the organiser, which is not in itself a bad reason. But in my view it does detract slightly from the excellent mapsmanship of the original organisers as Wickford is on a different sheet..