When I had 200lb springs on the back of my Sapphire, it was constanly trying to spit me side-ways off country roads, because instead of riding the bumps, it would skip over them (constantly breaking traction if you kept your foot in). The most IMPORTANT thing for good handling, is for the wheels actually to stay in contact with the road. I can assure you with these springs, you will get your arse HANDED to you by a well driven Mondeo (or another Sierra with softer rear springs ) on bumpy back roads .