The G16 had side-play on the trailing coupled axle to give some degree of flexibility - IIRC it was about 3/8" each way - a young Eric Langridge was all ready to work out a nice knuckle-jointed coupling rod and was slightly taken aback when the Finlayson (the Chief Draughtsman) told him to just give the trailing crankpin an extended journal surface. Clearly it worked. They were designed and built in parallel with Feltham yard, so a 7 chain radius had been agreed on. I believe the loco department were not best pleased when they found this had not been strictly adhered to and was causing derailments in parts of the yard, so the big tanks had to be given a bit more bogie side play. The spare G16 would also be used to cover part of an H16 diagram, if available, so they did get a bit further afield than just the yard.