Hi Rich,
I've just noticed that there are some Mini Cooper wheels advertised on Pistonheads. Assuming these are for the old style Mini then they may fit. The wheels are 13" but more importantly would have a PCD of 101.6mm which I think is what you need for the Viva hubs. The wheel offset is 13 which may not be suitable, but you may be able to sort this using spacers if the offset is wrong. The wheels are only £75 so could be a bargain if they fit!
If the wheels are suitable I could collect them and bring them up to the North East as I'm due in Newcastle in a weeks time. As to your question about 12" wheels I don't think these would look right. You would need to have tyres with quite a high sidewall. My wheels are 185/70 13 inch and fit the arches well. I think you woud need a tyre of 175/80 12inch to give you approximately the same circumference. I don't think these tyres are easily available. To check tyre sizes go to the link below.
A good website to explain different wheel and tyre options is Robs7. He started with 13" wheels on his Locost and changed to 15" ones. He explains how he decided on the size on the website.
Advert
http://www.pistonheads.co.uk/sales/2835673.htmMini Cooper Wheel Spec
http://www.leightyres.co.uk/catalog/pro ... bd3a3b3815Tyre size calculator
http://www.miata.net/garage/tirecalc.htmlRob Lanes 7
http://www.robs7.com/