Standard UK Zed runs on 225 Front and 245 rear with 7.5 and 8.5 wheel sizes I believe. Can I put 7.5 18" all round and just increase the tyre width on the back or do I really need to ensure front and back wheel sizes are different (7.5 and 8.5)?

If you're going for 18", 7.5J is sooooooo narrow. 225 is pretty much maxed out on that. IMHO, you want at least 9j at the rear with an 8j at the front. I've got 8.5J Front and 10J rear on my 18s.

If you're going for 18", 7.5J is sooooooo narrow. 225 is pretty much maxed out on that. IMHO, you want at least 9j at the rear with an 8j at the front. I've got 8.5J Front and 10J rear on my 18s.

 

What size tyres do you run and doesn't she wobble a bit when you hit imperfections in the road?

No not really. Fronts on mine are 235...but will be upgrading to 245. Rears are 265 but will be upgrading to 285.

 

It's not just about the way it drives, but the look needs to be right as well. You're aware of this by wanting to upgrade to 18". If you have a skinny set of 18s on the car, it won't look as good as standard UK wheels even...ie, it'll look terrible.

...infact I was running around on standard JDM wheels on it for a few weeks while I was getting bodywork done on it (7.5" all round) and it hardly felt any different. Firmer ride with my 18s on it, but no adverse road feel.