Hi , just joined and looking for some help. Looking to buy a set of aftermarket alloy wheels for my 67 plate smax titanium sport, to fit winter tyresThe current size is 235/50/18 offset et 55 and have been looking online at a set off 17 inch rondell OZ1 (215/50/17) the wizard selects it, but the offset is et45. will this make any difference ? 

https://www.tyreleader.co.uk/alloy-wheels-brands/rondell/01rz-4360/7.5x17-et45-5x108-70.4-645355?car=21082

Thanks in advance guys. 

No, that size wont be suitable as the overall diameter is different, you need to keep this the same. Generally if the wheel goes down a size then the profile will need to go up to compensate for the wheel being smaller and vice versa. Try comparing sizes on some online calculator tools like this one... https://www.willtheyfit.com/index.php?width=235&aspect=50&diameter=18&wheelwidth=8&offset=55&width2=215&aspect2=50&wheel_size=17&wheel_width=7-5&offset2=17

Personally, I would go for another set of Ford alloys and try to keep the same width tyre. My summer wheels/tyres are 235/40/19 and my winters are 235/45/18 on Focus ST250 alloys. I've declared my car as modified with winter tyres but the insurance wasn't bothered about the wheels as they are Ford branded. Not sure on this but you may need to declare those wheels as a modification as well as the winter tyres.

Would prefer to have a spare set of ford alloys but they are more than double the price.  I made a mistake with my sizes 

current ones are 235/50/18 and the rondell ones are 235/55/17 ( although it says in the technical max tyre width 225 although the technical at tyreleader assures me that 235 ( what the tyre and alloy wizard configures ) will fit