I've just changed 19" wheels with Continental Cross Contact to 18" wheels with Michelin Cross Climate.

Primary reason was to improve ride and add some all season capability without losing summer performance.

What I expected was improved ride, but thought I might get worse roll and "wander". All small differences expected. But what I got was quite different:-

Improved Ride and bump handling - but even better than expected (like what I hoped )

Much improved straight ahead stability - the car had been hard to stop "see-sawing", in a straight line or during gentle turns great focus was needed. With a 5-Series still in the garage, I thought this was just down to lack of experience with a softer suspended taller car. But these new tyres/wheels have eliminated this completely. (It wasn't a major issue, but it was there for sure)

I guess directly related to the above point, sharper and more accurate turn in.

The old tyres were all the correct pressure and I really can't explain this - can it really just be that the Michelins are just that much better a tyre? Old tyres were at 35 psi and new at 32 - recommended pressures for each size.

Car has 22,000 miles, so I would doubt worn suspension.