These pillion seats come up for sale now and then on ebay (examples shown) and jumbles,some times you can see the original green paint under the usually painted black post war finish (see below),they do not seem to be a standard fitment on any of the factory finished WD models,based on the design and style of them they seem to be lycetts.
above photo,the BSA M20 seems to have one of these seats,the Norton also looks like its been fitted with panniers and seat conversion.
Steve I'm pretty sure the saddle on that BSA is an "Acumen" The first long version had a padded hump added at the front as riders were hitting their coccyx bone on the hard edge. Later they made the "Acumen" short version. No doubt Jan can confirm. Ron
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I don't know... I've seen two of these contraptions before (the 4 spring short Acumen), and I've always thought that they were DIY conversions.
But now we have a third and a fourth (!) one, and they all look “exactly” the same.
Let's resume what we know about the Acumen pillion seats. The long Acumen came out in 1942, there was an Ariel and a BSA version (the rear springs were positioned differently). And for the reason that Ron already explained it was superseded by the short version for the very last WM20 contracts (1945 only). I can't imagine that the 4-springer (which was based on the short Acumen) was also introduced during the war, as I've never seen such a device in a war time photograph. (The pillion seat in your (post war) picture is a normal short Acumen Steve, I can clearly see the front bracket and the triangular reinforcement).
So I'm pretty sure these 4-springers are post-war, but while initially I was suspecting a DIY construction, it is hard to believe that several individuals came up with exactly the same result. These 4-springers must have come from the same supplier. The work is neatly executed, so they may perhaps have been made by Acumen with the remains of their WD stock?
Just my two pennies...
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