Many thanks, Noel.
I actually have no idea what how many teeth I'm after.
I've hardly ridden the thing.
The good news is that it wasn't such a dumb question after all.
I might get the suspension sorted, have a proper ride, then see what I reckon.
Seeing as mine's a 280, 47 might be close.
I'll get back to you if I think it's what I need.