tbh carl i didnt really want to move upto 17s with my car as i wanted wheel size as small as possible (being primarily a circuit car), but then a compromise had to be drawn between braking performance and wheel size and the brakes won!
what im trying to say to those people that have bought these brakes in the group buy is that there is a very high possibility in fact a certainty that your existing 17'' wheels will not fit over these calipers, you will need the alterations as in my last post.
im no conneseur of wheels but i would have thought you may even have the same trouble with 18'' wheels, theres plenty of clearance from inside of wheel to outer face of caliper, but its the face to spoke clearance that is the big problem here, and many 17'' wheels will simply not fit unless you put around a 20mm spacer on each wheel, which is far from ideal.
from what i can gather the smaller number the offset ie 37 fits better than 38 so you would need ideally around a 35 offset wheel, but then someone please correct me if im wrong
it maybe a good idea to copy this post in the group buy thread so people actually realise what expense there gonna have before buying the brake kit!