I've just had the 2nd new set of (rear) tyres put on my Turbo. The
make, markings, speed rating and compound are identical in every
respect to the previous ones. The front tyres have approximately 3K
miles left on them according to the fitter.

I know that new tyres take a while to "bed in" but the handling has
degraded terribly since they have been fitted (500 miles ago).  I've
noticed PSM kicking in four or five times a day on roads where it has
previously left me to get on with it.

The Drivers manual notes that handling will be affected if tyres of
different tread depths are put on opposite axles (especially
noticeable in the case of new rear tyres). I hadn't noticed this on
the previous tyre change - is it because the front tyres are near the
end of their life? (they were grippy enough with the old rear tyres).

I've ordered two new front tyres but I'd be grateful if someone more
knowledgable than me could explain the details of why this sudden
change in handling has occurred?

Thanks & regards,
Mike