tyres? and suspension?

Recently fitted Yoko A032R’s to my Sport 160, i was drawn to the fact i can have different compounds front and rear and wider front tyres, (Hard rear and soft front) understeer became a thing of the past. The car had standard P zero’s on before, so ahead i went, the rear’s i noted were 3mm larger in diameter, i thought if they rub on the rear arch trims i can just raise the car 3mm to compensate, you know with the ‘adjustable suspension’ well there’s the story i have more chance of passing a diamond down the crapper than raising the ride, as the adjusters have never been moved since new and are totally f*****g seized (deep joy) i cannot budge the adjustable spring platforms. Anyone got any suggestions apart from wearing down the rear tyres? the car is under extended warranty, but would they replace the spring items under warranty?Only thing i have been able to do is adjust the roll bar to cut down on roll, hellthe tyres can easliy handle it and it does stop the car moving about on the springs as muchHELP!