David I have a 2013 Narrow Body +4 it came with Avon CR6ZZ 185/70/15 and I have always bought the same but as you know they are very expensive at £356. It's my understanding that the composition is the same as the old F3 wets and I believe they are the tyre of choice for Morgan racers. I have always foud them to have superb grip especially in the wet. If you decide to go with the Blockleys I would welcome your opinion of them when you return as I am not far off a tyre change.
