Tire sizes

My uncle has a set of rims laying around with 225/35/18 on them.
 
Two of the tires are cracked, so im just gonna replace all four. The question is, rather then spending 150 per tire b/c they're low pros, can i just order some 225/40/18? They're less expensive plus not as low.

http://www.miata.net/garage/tirecalcold.html

Use this link to compare the tire sizes.  It should tell tou what you are looking for.  Also compare to your stock size.

They will not fit on that car in your profile..too big..you would have to roll the front and rear fenderwells to fit them on...
 
                                            WheelBrokerAng

215/40-18 will fit better than those options, but there's less of a choice in that size. It's the closest size to the stock 205/60-16 size. Only a 1/10 of an inch difference in diameter (smaller than stock).