So I bought some BBS RZs with tyres for the Scirocco today and it's all gone a bit slippy. Almost dangerously so. Some info:
Tyres have tonnes of tread (the ones I took off were on advisories).
Suspension setup hasn't changed. Wheels appear to sit fine on the ground (not on either edge etc).
Less grip on new wheels/tyres in both wet and dry. Thought it may have been the wet weather, but my other car was fine.
Tyres all at 28psi as they were checked before putting them onto the car.
Tyres are Mentor M300s. Never heard of them, but they don't appear aged/cracked/old etc. Rubber felt soft, but I'm no expert. Will check the date though.
When stood still, the steering wheel is lighter than before.
It's currently sliding more at the front, although I dare not test the rear.
I had been tinkering with the idea of semi-slick tyres at some point (R888R specifically), as I rarely drive in the wet, but that was a "nice to have" rather than a solid plan, but if it turns out my current tyres are crap, I may have to upgrade that to "oh go on then"!