I currently have drums at rear, and I m thinking of upgrading to disks, but which ones are suitable for the 1.4/1.6? My fronts, as far as I know, are 256mm. I ve seen Astras with 256mm at front and 262mm at rear(rear disk conversion from the 1.8/2.0 model??), but is this wise to do? Shouldn't the rear be smaller than the fronts?