A very generous collector from Melbourne has brought to my attention some info that pretty much closes the case on the introduction of plastic wheels. As requested, I won't post an image of the document, but its a page from the internal company memorandum (titled: Victa Cuttings), as circulated to distributors each month during that time. The following is the relevant excerpt, as it appears, un-edidted and unchanged:

Quote
VICTA CUTTINGS - MARCH 1957

WE ARE SURE YOU LIKED .... the new polythene wheels fitted to your most recent delivery of mowers. these attractive and durable wheels are fitted with nylon bushes, which require no lubrictation in the lifetime of the machine.

Complete with coloured hub-caps and black rubber tyres they are undoubtedly the most attractive mower wheels on the market and are yet another VICTA selling feature for your sales team to add to their list of victa advantages.

So as I theorised in earlier posts, polythene wheels were definitely introduced in either February or March of 1957 - more likely February, as this is a March circular.

This confirmation allows us to narrow down a production date/serial number correlation. Now all we need to find is the earliest confirmed "plastic" wheeled Rotomo serial number...