NCN13 can be taken from the end of Greenway Arc 2b var, but this extension route – starting as Cycle Superhighway 3 – is suburban, and inside the Oysterzone, so the 10-mile ride is best suited for local cyclists, commuters and complete-ists only.
However, after a very late recce (30-3-21) that found NCN13 east of CS3 to be a grim experience, with only a brief respite from road cycling on or beside busy roads with erratic cycle provision at best, a return the next day confirmed what mapping suggested: there was a very pleasant alternative ride passing by or through four parks - Greatfields 1.5, Mayesbrook 2.7, Parsloes 3.8 and Beam 5.7 - alongside the District Line tracks. There was also the startling bonus, having negotiated a porterage over railway tracks 1.8, of an Elizabethan manor house 2 nestling in a Barking housing estate. And current mapping had not caught up with LB Havering's recent investment in a cycleway through Beam Valley Country Park and Bretons Park 6.6, signed to link up with NCN136 at Ingrebourne Hill. This, and a trip north on Spin-off 1-2-3, is easily done by turning L on Grove Park Road 7.7 for the short link across.
However, Rainham Marshes Spin-off 3 and the Ingrebourne Valley offer a better more rural cycling environment, so the initial advice still largely stands good; take the C2C train from London Fenchurch Street, Limehouse, West Ham or Barking and start your ride at Rainham.