Grippy pillion seat cover - damn good investment ! Stops you getting squashed against the tank under heavy braking... When I carry anyone on the back of the ST I put slightly more pressure in the rear tyre (iaw the handbook, can't remember exactly how much off the top of my head) but I never bother adjusting the suspension. But then I never really go that fast two-up anyway...
Took the other half out again last weekend and the damn things still bottoming out. I will have to change the spring compression I think. As said above, never had to adjust any of my previous bikes.
