I don't know if it's needed on 2cv normally. I never needed it before, then I was worried about buying a new set of wheels and tyres thinking they might need it but it was still perfectly smooth.
A couple of years ago it developed a bit of a vibration and I really struggled to find a place that still had the adapter for the 2cv wheels, they need a centre hole to fit on the machine normally. Eventually a bloke in one garage told me of somewhere he thought might have this thing and luckily they did.
Just thought I'd post it up for info in case anyone needed it. They were amused and surprised to have a Deuche turn up after all this time
Britten Tyres, Reading RG2 0AU, 01189750005.