A couple of people have asked me about fitment. Going from 225/45 on 17" to 235/40 on 18", both ET35, has increased overall diameter from 634mm to 645mm. The tyre fills the wheel well by 5mm more. Testing it against GPS yesterday shows that my speedo is now almost spot-on, over-reading by 1mph at 70. Gearing is very slightly longer, but it felt just the same as before.
Poke is 5mm more and so is inner distance to suspension, so it's safe. Although the fronts look to be barely clearing the arches, there is no scrub on full lock.
Scrub radius remains the same, so the alignment that Abbey Motorsport did for me remains good.