in 1985*, a companion from England , riding the California Coast [SF South] with Me, used a Classic TA 50-28t Cyclotourist crankset.

Functionally such a big upshift out of the 28t would be done at the crest of a hill , so the strain on the chain is near zero.

* the freewheel, as I recall he used, was a 13-28t .. a 6 speed would be in that period.



My current rig (folding Brompton) the double is even wider , but the chain is not derailed, there is a gear box in the crankset,
the arms turn at a different rate, faster than the chainring, in Low reduction gear, range.


It ia functionally as if a 50 - 20 t double .. I combine it with a 3 speed IGH in the back wheel.. 6 speed, no overlap, results.

Both being planetary, 3<>4 is a quick double shift.