Need help with tyre size

[koi]

Need to get 2 new tyres but just wondered if I could fit a slimmer tyre?

Got Goodyear Eagle F1 GS-D3 215/40 R16 86W on it just now.

Cheers

 

[Laura]

depends how wide your wheels are

 

[koi]

How can I tell how wide they are?

 

[koi]

Right just had a look and it has 7Jx16H2 stamped on it.

What tyre sizes can I fit? Also will I have any problems with the front and rear being different sizes?