165/55, cheap, decent tread and grip and not TOO much of a pig to stretch.
8.5J is the maximum I would recommend for them as it's a ton of stretch! But they look banging on 7J and 7.5J.
Check out my blog, I have 165/55/13 fitted on 7,5J and 8,5J
175/50/13 are tiny bit wider but also have a smaller sidewall, so the stretch is virtually the same