Not sure if the streering vibrate issue is caused by your tyre or not.
My small little Myvi has been using CC5 195/50 R15 for around 1 year & 5 months and I have no issue with steering vibration. The mileage for my tyre is almost 30,000km and still got approx 25-30% of tread left for running. I did allignment & balancing every 15,000km. Did speeding as well up to 180km/h, a very little bit of steering vibration only which is normal to me.

*edited for typo

This post has been edited by Mau: Sep 13 2012, 07:58 AM