Last night I had the somewhat disturbing experience of the dynamo not engaging properly on the wheel due to the wet conditions. ie I was riding on dark wet roads with no headlight.
I got home and experimented by rotating the dynamo mounting so that it is more centred on the tyre. This morning the roads were still wet but the dynamo seemed to be working fine.
It does raise the possibility of having to adjust the dynamo mounting whenever I change the type of tyre used on the rear wheel. Mind you I've only done that once so far so not really a big deal.