Hi everyone, I experience the same on my 2013 1.6 GLS with normal tyre pressure. If the imperfection on the road surface move underneath both wheels at the same time, there is no problem. But as soon as one of the wheels move over a small hump (± 25 mm) on the road surface the whole rear end became unstable even at 60 km/h. At everything above 13o km/h the car is nearly uncontrollable if there is a long stretch of imperfections. I just aim the steering straight forward. I've already put ± 25500 km on the clock so the suspension can not be too stiff anymore. My 2013 i10 does not have any of the problems under the same conditions.