[EricH]

254 has a "mobile" sprocket system, where the end bearing blocks get pulled outwards/inwards to tension the chain. The only things on the chain are the gearbox sprockets and the wheel sprockets (it's a live-axle system). I don't know how they compare, but there aren't a lot of people who use the bearing-block tensioning system that I know about. So it seems reasonable that they look at the basic drive system without regard to the tensioners.