By calculation 235 40 19 ( 92Y ) should be easily good enough.
I was looking into load index of tyres and what the reccomendations for the 159 are 235 40 19 (96Y)
This equates to 710 kg per tyre upto 190 mph ! ! ! !
Ive only done it for the 1.9JTDM but a 235 40 19 92Y is still plenty sufficient for this vehicle. Someone please correct my conclusion if ive miscalculated....
As a rule you need to allow for 25% extra weight per tyre to allow for weight change to the tyres like speed bumps ect.
The curb weight of a 159 is at max 1680kg + 25% (420kg) = 2100kg, devide this by your 4 tyres and its load rating is 525kg, as opposed to the 710kg of a 96 load tyre and beings the car wont scrape 140mph you could even resort to a W speed rating.
A 92Y handles 630kg per tyre and upto 190mph .... this tyre is more than sufficient for a 159... i know theres the bla bla manufacturer spec / insurance argument. but its in black and white they can safely be used.....
or am i way off the mark ?