Just wondering if it's possible for 2018 cx5 rims to fit straight onto a 2013?

Tia

 

You'll have to measure the off set on both wheels. There are a few differences but I don't know if they will stop you. Try looking here;

https://wheelssize.com/wheels/mazda/cx-5/

I think there was a major redesign in '16, but I don't know if it was mostly body or heavy mechanical. Sometimes a redesign is just a few details.

 

Yes, 100%.