Poor visibility was always an issue with the original Beetle and its split back window. Volkswagen addressed this in March 1953 when the screen was replaced by a larger single-piece oval one. This important change coincided with the beginning of sales in the UK, and all but the very first of the ‘Oval Beetles’ benefitted from the first increase in engine size since 1945 when an 1192cc unit added 5bhp. With 30bhp to play with now, 66mph was possible... not much on paper but, of course, a Beetle could happily cruise at this speed all day. Add 25% for Cabriolet prices.
info from Octane