Quote Originally Posted by Diesel_vert View Post
A 255/35 R19 tyre will have a higher sidewall height (255 x 35% = 89 mm) than a 235/35 R19 tyre (235 x 35% = 82 mm), hence the increase in compliance.

In addition, the tread depth will be at its greatest when the tyres are new, which also contributes to the feeling of increased compliance, but this will diminish as the tyre wears down. Also, the compound tends to harden with age, so the tyre is softest when new.

To put it in a bit of perspective, that's usually the experience of most (but not all) people when replacing a set of old or worn out tyres with a brand new set.
Actually the original tyres were 235/40R18 which is 94mm sidewall height (technically more compliant), but your probably right about the extra tread depth on new tyres giving better compliance. Not forgetting it is also a totally different and softer compound with totally different side wall construction and different tread pattern also. They also officially quote them as being quieter than the old Conti 3 and also have a 5P version designated RO1 which is 9dB quieter. (dont think I got the RO1 but I havent checked)