Help with Wheels

[FREESTYLE_MX]

Hi,
At the moment, I have 16inch rims with 225/50r/16 tyres on them.I am soon to be getting new mags and tyres which are 235/40r/18. I did a tyre calculator test and these were the results:
http://www.1010tires.com/TireSizeCal...?action=submit

I dont know what i`m looking at there, but I was just wondering if they were legal. Making the jump from 16`s to 18`s, I read that they had to be 15mm less or something ( 15mm rule)? Just wanting to know if they were legal and all.

Cheers Ash

[sleeper5L]

18 inch wheels are legal as long as your car had 16 inch wheels as standard.
As far as the tyre width... 235 is fine.